Pico-Engine Non-Invasive testing Webinar Q & A

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Steve Smith
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Pico-Engine Non-Invasive testing Webinar Q & A

Post by Steve Smith » Mon Jun 03, 2019 12:04 pm

Practical Pico - Non-invasive engine condition testing Q&A

Many thanks once again to those who could attend the following Pico Practical Session https://www.youtube.com/watch?v=fEqC2ZFWNdI and for the questions raised on the night that could not be answered fully.

Below I will go through the outstanding questions and hopefully clarify any outstanding queries:

Whilst a number of questions were not specific to the topic (Non-Invasive engine condition testing) I will add them accordingly.

Please forgive my failure to write down the names of those who raised questions and I sincerely hope these answers find you.

Question 1.
A question was raised about the minimum permissible battery voltage during cranking along with the Pico Diagnostics battery test results:

This is an interesting question especially if you have previously captured the minimum battery voltage during cranking with a multi meter. In this scenario we are likely to see a momentary average of the minimum voltage (or RMS) depending on the meter. With PicoScope we have the ability to capture voltage at lightning speeds with numerous samples where we acquire the true value of battery voltage at the instantaneous point of inrush current into the starter motor

This has always been the case but never visible with a multi-meter and a number of technical publications refer to a multi-meter value as the minimum cranking voltage rather than the scope (which was often considered overkill for cranking voltage measurements!)

The capture below has a perfectly healthy battery voltage momentarily falling to 8.841 V yet the DC Average is 10 .51 V
IMAGE 1.png
Battery Voltage during cranking
Both PicoScope and the Pico Diagnostic battery test would capture and record this instantaneous low voltage but our multi-meter could not. With that said, I think we would be happy to accept this momentary 8.841 V even though a number of technical publications might suggest we are approaching the limit of acceptance at 8.6 V.

We need to interpret the results obtained and apply them accordingly on a case by case basis, underpinned by our theoretical knowledge. Had this battery voltage fell dramatically to 8.6 V during initial cranking and continued to fall whilst cranking, we most certainly have alarm bells ringing. Using the scope means we have the ability to evaluate the effects upon voltage over time, unlike the multi-meter.

The following posts will help with how the Pico diagnostics battery test will evaluate and display your battery condition during the crank and start phase of an engine

https://www.picoauto.com/support/post77701.html#p77701
https://www.picoauto.com/support/post57461.html#p57461

I hope this helps, and if I have misinterpreted the question raised please feedback when you can

Take care…….Steve

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Re: Pico-Engine Non-Invasive testing Webinar Q & A

Post by Steve Smith » Mon Jun 03, 2019 4:31 pm

Question 2.
Dealing with the Fiat Twin Air “in cylinder” pressure captures and multiple variables.

I am not sure how this came about but I certainly scribbled it down on my pad during the webinar.
“Multiple variables” are the challenges we face with diagnosis and engine evaluation is one such example.

Think about a vehicle that is presented to you with a misfire (combustion anomaly) and the initial data/scope traces that you capture on arrival.

These may lead you to a near conclusive diagnosis until you stop and think about the running condition of the engine and the PCM’s ability to compensate / mask the fault we are trying to diagnose.

We witnessed these exact same variables when testing the exhaust gas pulsations on Ben’s Mazda 3 Petrol with the 2.0 litre SkyActiv engine and his relative compression test.

On one occasion we increased the exhaust pulsations by blocking one of the tailpipes, then repeated the test the next day to find the complete opposite!

Whilst I cannot explain the exhaust pulsation variations, I know the Mazda SkyActiv engine has some unique cylinder pressure characteristics post start up, all of which can influence exhaust gas pulsations

The relative Mazda compression test also threw a curved ball with very low compression peaks within the starter motor current.
IMAGE 2.png
Mazda Relative Compression
Note the peak current flow during cranking at approx. 40 A and the peak to peak value of just 8.6 A between compression events!

With this in mind, good practice with any capture:

1. Blame your measurement technique first, look for measurement error, set up error and misinterpretation of results.

2. Blame your measurement conditions (E.g. hot/cold engine, battery fully charged etc.)

3. Once you are happy the results are factual, then qualify the results against known good under identical test conditions. (Minimise the variables)

If you carry out an in-cylinder pressure measurement and start the engine of the Mazda SkyActiv unit you will certainly notice a change in the exhaust tone approx. 20 seconds after start up (depending on temperature) accompanied with a change in cylinder pressure
IMAGE 3A.png
Mazda In cylinder Pressure Post Start Up
The image above highlights this intriguing event where a dramatic change in compression occurs (with minimal change in engine speed) thanks to throttle position and elaborate valve timing.
N.B. the WPS500 x voltage output above is 1 V per 100 psi / 6.894 bar

A discussion with Mazda highlighted another clever feature of the SkyActiv petrol engine whereby it has an anti-flood mode, allowing the engine to clear excess fuel from the cylinders after a partial non start. Again this is achieved via valve timing and throttle position whereby the engine appears to crank rapidly with very little compression! (Imagine carrying out a compression test whilst the PCM is carrying out "anti-flood")

The Fiat Twin Air system was mentioned during the webinar as one of those vehicles demonstrating such variables whilst attempting to diagnose reported faults.

There is a fantastic case study here from Mark Stammers https://markstammersdiagnostics.com/casefiles/fiat-twinair-misfire/ which highlights the additional challenges we face from the PCM when it comes to battling with variables. The Waveform Library has a number of Fiat Twin Air captures that may help should you find yourself up against these vehicles.

The included paragraph “The more I read up on the system, the more I had to think about ’cause or effect’, as this system has the ability to control the intake valve opening duration, advance/retard and lift, per cylinder per stroke! wow! What a challenge!” kind of sums up variables

Another example of shifting variables is a vehicle that appears to be “falling apart” whilst in your care! The kind of vehicle that is driven in and then pushed out! The VW Polo Case study is one such example here: https://www.picoauto.com/library/case-studies/vw-polo-misleading-fault-codes

To summarise here, product knowledge is invaluable and reduces diagnostic time. This is a good case for specialising in specific brands which by its nature, allows you to collect product knowledge that is not even documented but gathered through experience. (Awareness is key and king)

I hope this helps and I hope it goes some way to answering another challenging question.

Take care......Steve

PS more Q & A's to follow ASAP

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Re: Pico-Engine Non-Invasive testing Webinar Q & A

Post by Steve Smith » Thu Jun 06, 2019 7:53 am

Question 3.
Can you confirm the fluids that are compatible with the WPS 500X Pressure Transducer?

If we follow the owner’s manual (see link further down) to the letter page 8 states:

Compatible fluid types
The WPS500X is suitable for use with the following types of fluid:
• Gasoline and diesel (low pressures only – see warning on p. 2)
• Engine oil
• Air

I guess the best way to approach this is to look at the construction of the WPS which utilises Viton seals throughout. Based on this alone I have then found the following link to the Wikipedia site https://en.m.wikipedia.org/wiki/Viton that lists the general compatibilities of Viton seals. (No doubt there will be others)

With this in mind, I know the WPS500X has not been tested with Brake Fluid and R134A gas but I have used the WPS to measure both these pressures with no effect on the transducer.

We have to be mindful of the corrosive aspect of the fluids we intend to measure (e.g. AdBlue) as the WPS housing/measurement chamber should also be considered as well as the seals

In all cases of using the WPS to measure “fluids/gases of doubt”, I would ensure the unit is washed out thoroughly post-test to preserve the integrity of the measurement chamber & seals whilst also avoiding cross contamination

The clean procedure can be found on pages 10 & 11 in the link below
https://www.picoauto.com/download/documents/manuals/DO157-14_TA071_WPS500X_Users_Guide_web.pdf

Returning to R134A for a moment, as an experiment we have created the hoses below to enable WPS to be connected to an AC system! This opens up a whole new world for AC Diagnosis and training as we capture pressure against time with superior resolution
IMAGE 4.png
AC Hose Experiment
With reference to the following case study https://www.picoauto.com/library/case-studies/ford-focus-engine-overheating & using the specially adapted hoses above, a brief evaluation was made on the operation of the AC system at idle speed with the cabin controls set to “Max Cool” and all vehicle doors open. This will load the AC system as it attempts to cool down the atmosphere at an ambient temperature of 26° C!

The waveform below highlights cooling fan operation, along with the pressure values contained within the High and Low AC pipework. Given the ambient temperature and the loading of the AC system, I would expect to see the high pressure to increase to approx. 10 bar and remain around 2 bar on the low pressure side. Based on this quick evaluation in conjunction with poor cabin vent temperature a recommendation was made to inspect the refrigerant level.
IMAGE 5.png
AC WPS Waveform
To analyse the AC pressures a little further, we can see the compressor to be functioning correctly as during the compressor “off stage” the pressure equalisation time was approx. 12.5 seconds suggesting no rapid equalisation as a result of internal compressor leakage between the input and output ports. The rise/fall time of the compressor during the “on stage” was also respectable at approx. 5 seconds with no drop out.

Please note one again that the WPS has not been tested with R134A refrigerant gas, but I can say that both these WPS units remain in use and have suffered no internal damage

Be aware of the maximum operating temperature of the WPS at 60°C as this can be exceeded with AC measurements

I hope this helps……take care……Steve

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Re: Pico-Engine Non-Invasive testing Webinar Q & A

Post by Steve Smith » Tue Jun 11, 2019 9:53 am

Question 4.
1. Testing 3-Phase Motor/Generators using existing Pico accessories
2. How do we profile current flow through these motors

Before we begin here there are a number of Do’s & Don’ts when testing HV & EV vehicles.

Awareness, Working environment, Training, and current Qualifications are paramount when testing HV systems as the safety to yourself and others cannot be compromised.

Prior to measuring HV systems, ensure the correct shutdown procedure has been followed as per the manufacturer instructions and confirm/qualify zero potential

For measuring current we have a number of AC/DC current clamps here: https://www.picoauto.com/products/current-clamps

For voltage measurements we have our Differential Probes here: https://www.picoauto.com/products/electric-and-hybrid-vehicle for voltages up to 1400 V

For AC Current measurement of 3 phases simultaneously we have the specialised AC 3-phase flex current probe here: https://www.picotech.com/accessories/current-probes-clamps/30-300-3000-a-ac-3-phase-current-probe-bnc
There will be more to follow but that is enough said for now!

The automotive application of the above 3-phase flex current probe can be seen here: https://www.picotech.com/oscilloscope/4444/picoscope-4444-applications but I must add, the Tesla Roadster used allowed easy access to such cables. The more “mainstream” brands have very limited or simply no access to each phase (depending on construction) and so other forms of testing are required.

The accessories above predominately apply to live measurements of Voltage and Current which is most certainly relevant for glitch capture, intermittent errors and training.

In reality, vehicle manufacturer’s request that fault codes, serial data & flow charts are adhered to, combined with post shutdown HV system testing (zero potential confirmed)

Testing of the Three Phase Motor/Generator would therefore consist of Insulation and Micro-Ohm measurements to confirm integrity of the windings/assembly

Returning now to profiling current, using the Tesla capture in the link above with the 3-phase flex current probe (you could also use 3 x current clamps) , I have used maths to profile the RMS current flow via the motor windings (The equivalent DC current)

Given the 3 phase flex probe and DC current clamps were originally used without the relevant custom probe settings, I have converted the values captured on channels A, B, C & D from voltage into current (probe output 1 mV/A)

Channel A, B, C & D are therefore multiplied by 1000 and converted to amps using the formulas A, B, C & D*1000

Below we have the three phase current measurement converted from voltage to current
ORIGINAL CAPTURE.png
Original Capture
To calculate the RMS current we then use the math channel formula:
“sqrt(integral(A^2)/T)+sqrt(integral(B^2)/T)+sqrt(integral(C^2)/T)*(1000)”

We can now graph the equivalent DC current through the windings of the motor/generator so creating a “profile”
DC AVERAGE OF 3 PHASES.png
3 Phase Current Graphing/Profiling
Please don’t be put off by the math channel formula, it is the same as this single phase measurement here only repeated three times for three phases. N.B the x1000 at the end of the formula is to increase the final values due to the initial probe settings using voltage rather than current (1 mV/A)

Having this formula loaded into your math channel library will be useful for other 3 phase applications such as Fuel Pump and VVT actuators that utilise 3 phase motors.

Many thanks again to Martyn, Pete and Ben here at Pico for there support with the above.

I hope this helps, take care…….Steve

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Re: Pico-Engine Non-Invasive testing Webinar Q & A

Post by Steve Smith » Tue Jun 25, 2019 10:54 am

Question 5 (YouTube comment LINK TEXT HERE)

Can you tell me if disabling the PCV system will affect the crankcase waveform? Similar to blocking off the excessive loss in the exhaust by capping off one outlet. I would assume that the intake vacuum will have some influence on the waveform by way of the PCV system. Have you done any comparisons with and without the PCV involved?

Thank you for the above and like everything, access is everything and the PCV valve is no exception.
Recent testing of a 1.8 litre Prius enabled a comparison crank case pressure test with PCV operational and then blocked. The test below was carried out at idle speed only with a warm engine.

PCV BLOCK.jpg
PCV Blocked

Blocking the PCV most certainly increases crankcase pressure which will improve resolution and will amplify anomalies that may be disguised under normal crankcase “breathing” conditions.

Interesting how idle speed was affected during the “blocking” and releasing of the PCV hose (78 rpm) but not surprising given the conditions within the intake manifold will change without crankcase fumes contributing to air flow.

Where possible momentary blocking of the PCV whilst monitoring engine speed at fixed intervals (1000, 2000 & 3000 rpm) could be utilised to provide a crankcase pressure “signature” during routine maintenance (reviewed during each service) or a technique to adopt during diagnosis.

I hope this helps, take care……..Steve

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Re: Pico-Engine Non-Invasive testing Webinar Q & A

Post by liviu2004 » Tue Jun 25, 2019 6:27 pm

As far as I can google, the AC compressor safety valve opens at around 40 bar. If WPS500X is ok to 34.5 bar, what is the pressure when it will blow up?

If we talk about probability. Well, it happened to me few years ago. So lets say once in a lifetime for one person working in the industry. I was lucky to be inside the car, but what if the person is with the wps500x in the neighborhood when this thing blows up? Lets say major injury or fatality for a product Pico sells?

I am in doubt if this product should be advertised for AC systems at all!

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Re: Pico-Engine Non-Invasive testing Webinar Q & A

Post by Steve Smith » Wed Jun 26, 2019 2:49 pm

Hello and thank you for the feedback surrounding AC Compressor safety valve operation.

You are most certainly correct about the specified peak operating pressure of the WPS500 at 34.5 bar and therefore in extreme circumstances, the AC pressure could exceed the maximum specified operating pressure of the WPS 500.

I agree entirely with “talking about probability” as I am a firm believer in the phrase “if it can happen it will happen”

What we can be assured of is that industry standards ensure “Test Pressure” is considerably higher than the operating pressure to present a safety factor.

The safety factor depends on the regulations that apply to the device under test (WPS500) and to the industry in which the pressure sensor is designed to operate.

Typical safety factors are between 140% and 166% of the designed working pressure.

If we apply 140% rule then the WPS will have been tested to 48.3 bar and no doubt beyond.

With all that said you are absolutely correct, we should not operate the WPS500 in an environment where it could be subjected to pressures or temperatures beyond the maximum specified operating range.

Thank you again for the feedback, take care…..Steve

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Re: Pico-Engine Non-Invasive testing Webinar Q & A

Post by Steve Smith » Thu Jun 27, 2019 9:08 pm

Question 6 Relative compression testing of Hybrid vehicles (48 V Mild Hybrid)

This is an interesting question for sure and one we are all going to ask given these vehicles will be “mainstream” long before full EV’s arrive.

I am in the process of trying to locate a 48 V Mild Hybrid in order to carry out a relative compression test using PicoScope. Once I have the results I will post them here for review and discussion rest assured.

Whilst the search continues I thought it would be a good idea to look at a Power Split Hybrid (Prius) as these vehicles are widespread in various forms from Toyota/Lexus

The relative compression test can be handled using the scan tool “Hybrid System Utility” menu to place the vehicle into Compression Test Mode. Here the fuel and ignition system are disabled and the engine is rotated via Motor/Generator 1 (MG1) at approx. 250 rpm (Sound familiar?)

The same procedure applies if you wish to rotate the engine to carry out an absolute compression test with a gauge or pressure transducer.

Using the scan tool software we then graph the speeds of each cylinder to determine “balance” between cylinders based on their respective speeds.

I must add here that during cranking the engine/transmission emits an awful knocking/clanging noise which is typical of these hybrid units thanks to the planetary gear arrangement (power split device) and transmission input damper. (Similar to a clutch plate)

The question therefore is how we measure cranking current/voltage (to obtain relative compression) with these systems whilst the engine is rotating, given MG1 utilizes a 3 phase voltage and current via the High Voltage system?

In an ideal world you should not have to, but if you do, the relevant training and qualifications are paramount

Looking at the image below, (good compression) we can see that HV battery voltage, current & MG1 “W1” phase current reveal very little relevant to the engine compression events!

TEST 5 REL COMP WITH SINGLE PHASE MG1.png
Good Compression

What is interesting about the above capture is the low level of current required to crank the engine thanks to the high DC voltage!
DC current flow from the HV battery to the invertor (approx. 5 A DC)
AC current via W1 winding of MG1 (approx. 4.5 A AC)
Note also the minimal voltage ripple present at the HV DC battery. (approx. 206 V DC)

I think we have to agree that to confirm relative compression to be serviceable from these signals alone is going to be challenging!

However using a math channel to graph the crankshaft sensor signal will reveal the acceleration and deceleration of the crankshaft during engine rotation via MG1

More information on math channels can be found here: https://www.picoauto.com/support/topic21311-10.html#p97972

I have used 2 x math channels in the image above to try and remove the impact upon the “Crank” math channel from the missing teeth of the pick-up ring, as no data is drawn when using Crank(A,36) at each missing tooth

I am not sure if it helps but I have included the following alternative LowPass(60/36*freq(A),50) if required?

The math channel highlights uniformity across 720° of crankshaft rotation with an equal fall in crankshaft speed during the compression event (approx. 90 rpm)

HYBRID RELATIVE COMPRESSION.png
Good Crank Math-Good compression

Note how during the acceleration of the crankshaft (post compression TDC) we have captured a momentary reduction in crankshaft speed (almost like an interruption to acceleration).This event maybe caused by the delayed closing of the intake valve during the compression stroke of the opposing cylinder (approx. 60° ABDC) and demonstrates the Atkinson Cycle used for this style of engine. The intake valve close event can be delayed by up-to 102° ABDC which is amazing when you think your effective compression is generated in only 78° of crankshaft rotation!

Another possibility is the intervention of planetary gear “activity” given MG1 rotation is connected to the crankshaft via a planetary gear set and transmission input damper. More investigation is required but great for future knowledge.

Below we have the same compression test but with cylinder 2 spark plug removed. We must bear in mind that removing a spark plug is not the most realistic representation of a low compression, such as a poorly seated valve which will allow for some compression to build and therefore apply load to MG1.

With the spark plug removed we introduce a dramatic, momentary acceleration of the crankshaft which introduces backlash with the planetary gear arrangement between MG1 and the crankshaft. (I believe we can this activity in the math channel below)

CRANK PLANETARY ACTIVITY.png
Low Compression Math Channel

I have annotated the sections of the math channel waveform where no data is drawn due to the missing teeth. Whilst this may not be 100% accurate it helps to reveal the trend of the crankshaft during the “passing” of the missing teeth

Notice above how we now how 5 events within 720° of crankshaft rotation instead of 4! (Planetary gear activity) We can see how the crankshaft uniformity has been lost, and the speed fails to decrease sufficiently during the compression of cylinder 2 followed by a dramatic acceleration. (Peak to peak rpm is approx.162 rpm)

Based on the above we can conclude the crankshaft sensor remains our best option with these hybrid systems when evaluating compression in a non-intrusive fashion. Another option maybe the Resolver (speed and position sensor) for MG1 which again is another avenue to explore in the future

I hope this helps, take care…….Steve

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Re: Pico-Engine Non-Invasive testing Webinar Q & A

Post by Steve Smith » Tue Jul 02, 2019 12:01 pm

Question 6 48 V Relative Compression follow on.

With thanks to Audi UK I have been able to capture such data from the following vehicle:
A8 V6 3.0 TDI (2018) 48 V Mild Hybrid Electric Vehicle (MHEV)

As the name suggests (Mild Hybrid) the vehicle utilizes 48 V cranking, charging, advanced stop/start (engine off during coasting) recuperation & boost function for the ICE. More information on the Audi Mild Hybrid system can be found in their SSP 664

What a Mild Hybrid cannot do is drive the vehicle solely on electrical power unlike other options which include Series, Parallel, Dual and Power Split Hybrids

The 48 V Mild Hybrid in its simplest form utilizes a 48 V Motor/Generator (MG) connected to the crankshaft pulley via a poly V belt. The MG therefore functions as our starter motor and generator where the 48 V output (when charging) is converted from 48 V to 12 V to charge the 12 V battery. (Note: The vehicle has a 12 V and 48 V battery)

One additional feature of the A8 is that it still utilizes a conventional 12 V starter motor for starting the engine from cold! I am not sure why or whether this is specific to the Diesel model only, but I guess that is a topic to discuss another time.

What I did note whilst working with this vehicle is that when I introduced a fault or allowed the engine to cool, it would crank via the 12 V system.

Below we have the vehicle starting via the 48 V system:
Peak inrush current approx. 251 A into MG
Battery voltage during cranking approx. 40 V (48 V battery)
Battery voltage during cranking approx. 11.15 V (12 V battery)

IMAGE 1 48 V START.png
48 V START

Below we have the vehicle starting via the 12 V system:
Peak inrush current approx. 852 A into MG
Battery voltage during cranking approx. 47.5 V (48 V battery)
Battery voltage during cranking approx. 6.68 V (12 V battery)

IMAGE 2 12 V START.png
12 V START

Looking now at relative compression testing using 12 V starter motor current (Good compression) It’s pretty much business as usual where the crankshaft sensor can be used to provide an overview of acceleration and deceleration. Note the uniformity to both starter motor current and crankshaft speed.

IMAGE 3 12 V RELATIVE COMPRESSION.png
12 V REL COMP

Below we have now lost uniformity of the crank sensor signal due to no compression on cylinder 1 (Glow plug removed). Both signals can be used to determine compression loss.
IMAGE 4 12 V RELATIVE COMPRESSION -BAD.png
12 V LOW COMP
Moving now to 48 V cranking non start with good compression:
To determine relative compression from voltage and current here looks challenging at best!

IMAGE 5 48 V RELATIVE COMPRESSION -GOOD.png
48 V REL COMP

Looking closely at the crankshaft sensor signal we can see how the engine rpm rises and falls uniformly for every rotation of the engine! Whilst I have no comparison to make, there are no faults with this vehicle and we must therefore conclude that this is characteristics of cranking via the 48 V MG

Average cranking speed approx. 550 rpm!
Deviation in cranking speed between engine rotations approx. 238 rpm!
We therefore need to focus on the uniformity of the pulsations within the cranking speed fluctuations in order to determine compression events

IMAGE 6 48 V RELATIVE COMPRESSION -GOOD.png
48 V REL COMP PULSATIONS

Below 48 V cranking non start with bad compression (Glow plug cylinder 1 removed) and disruption to the uniformity of our crankshaft sensor signal.

IMAGE 7 48 V BAD COMPRESSION.png
48 V LOW COMP

Look a little closer and we can see the effects on crankshaft signal uniformity thanks to loss of compression on one cylinder.

IMAGE8 48 V BAD COMPRESSION.png
48 V LOW COMPRESSION DISRUPTION

With all the above, we can therefore conclude that the crankshaft sensor signal is going to be paramount for future relative compression tests for all forms of Hybrid vehicles.

I hope this helps, take care…….Steve

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Re: Pico-Engine Non-Invasive testing Webinar Q & A

Post by Steve Smith » Tue Jul 02, 2019 12:49 pm

A little off from Hybrid but in keeping with engine testing....

I thought it would be useful to include the Mazda Rotary Engine compression testing too:

https://www.picoauto.com/support/post35111.html?hilit=rx8#p35111

Take care......Steve

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