Lotus Esprit with low compression

Everyone loves a happy ending. Share your diagnostic success stories here.

Lotus Esprit with low compression

Postby Alan » Mon Mar 07, 2011 2:41 pm

The case study section of our forum is new, so to start things off we have decided to feature one of our own cars.

Unlike a normal case study we honestly do not yet know whats wrong with this car. We want you, the readers to post suggestions as to what we should do next ! We will then carry out the tests (so you do not have to get your hands dirty) and post the results. Hopefully this will be fun and we may end up learning something useful.

The car
Todays subject is a 1996 Lotus Esprit S4s with 70,000 miles (112,000 km) on the clock. This has a 2.2L 4 cylinder turbocharged engine that produces around 300BHP. It is standard with no modifications.

rolling road small.jpg



The symptoms
Whilst testing a new beta release of PicoDiagnostics we performed a relative compression test and got the following:

Lotus compression.gif


Now this may seem like a simple case of an engine with poor compression however the car seems otherwise to be in good health. It is outputting > 300BHP and recently did a 0 to 60mph sprint in 4.5 seconds. These performance figures are similar to some tests done several years ago and are close to the published performance specifications when the car was new.

What do you want us to check next ?
Alan
Pico Staff Member
Pico Staff Member
 
Posts: 239
Joined: Thu May 25, 2006 8:02 am

Re: Lotus Esprit with low compression

Postby mapengo » Tue Mar 08, 2011 6:21 pm

Can you repeat the relative compression test as follows please:

1. Using the WPS in cylinder one as a synch so we can see the pressures
2. Show us the sync signal in the top half of the screen
3. Repeat the same test using the 600 amp inductive clamp and Cyl1 sync with WPS

Can you do a cylinder balance test showing the variation results?

Cheers

Doc...
mapengo
User
User
 
Posts: 16
Joined: Sat Aug 30, 2008 9:08 pm
Location: Warrington, Cheshire

Re: Lotus Esprit with low compression

Postby Alan » Wed Mar 09, 2011 9:16 am

Hi Doc,

It was a bit late when I captured these and apologies but I did not read your tests carefully enough. I captured using PicoScope when you wanted PicoDiagnostics. I think it still gives you the data you want though. If not let me know.

Cylinder 3 pressure using WPS500 and cranking current.
(Warm engine, cranking with WOT).
cylinder 3 pressure and cranking current.gif

WPS and starter current cranking cyl 3.psdata
Cylinder 3 pressure using WPS500 and cranking current
(1.1 MiB) Downloaded 606 times


I used cylinder 3 rather than 1 as access was easier. Note the compression for cylinder 3 at 130psi (8.96 bar). From the current trace we can see that cylinder 4 looks odd (1-3-4-2 firing order). Lets look at cylinder 4

Cylinder 4 pressure using WPS500 and cranking current.
(Warm engine, cranking with WOT).
cylinder 4 pressure and cranking current.gif

WPS and starter current cranking cyl 4.psdata
Cylinder 4 pressure using WPS500 and cranking current
(1.23 MiB) Downloaded 579 times


The pressure on cylinder 4 is 89.7psi (6.1 bar). From memory we are supposed to have > 110psi on this engine.

Next is the cylinder balance test. I did struggle a little here - all Esprit 4 cylinder engines run pretty rough at idle (they sound a bit like a cement mixer full of bricks) so the results jumped around a bit. I had to put the lights, heated screen and air-con on before the results settled down a bit.

Cylinder Balance Test
Esprit cylinder balance.gif


At times the result was close to 100% on each cylinder. This fits in with the fact the car seems 100% OK when driven (we only found the low compression by chance).

OK - what do you want us to do next !
Alan
Pico Staff Member
Pico Staff Member
 
Posts: 239
Joined: Thu May 25, 2006 8:02 am

Re: Lotus Esprit with low compression

Postby mapengo » Wed Mar 09, 2011 11:05 am

Hi Alan,

Can you post a link so I can download the psdata of the two relative compression tests please.

I want to have a closer look at the valve events on cylinders 3 & 4.

Cheers

Doc...
mapengo
User
User
 
Posts: 16
Joined: Sat Aug 30, 2008 9:08 pm
Location: Warrington, Cheshire

Re: Lotus Esprit with low compression

Postby Alan » Wed Mar 09, 2011 3:22 pm

Original files added to the post above.

Alan
Alan
Pico Staff Member
Pico Staff Member
 
Posts: 239
Joined: Thu May 25, 2006 8:02 am

Re: Lotus Esprit with low compression

Postby mapengo » Wed Mar 09, 2011 8:54 pm

Thanks Alan,

Can see some subtle differences in the compression waveforms, will download Thursday at work and have a look.

Cheers

Doc...
mapengo
User
User
 
Posts: 16
Joined: Sat Aug 30, 2008 9:08 pm
Location: Warrington, Cheshire

Re: Lotus Esprit with low compression

Postby Alan » Thu Mar 10, 2011 9:05 am

I know we said we would do the tests suggested by forum members, but whilst we had the WPS500 pressure sensor in each cylinder we could not resist doing a running compression test.

Cylinder 3. Running compression, snap throttle test
koer snap throttle 3.gif

KOER SNAP-THROTTLE-3.psdata
(704.24 KiB) Downloaded 584 times


Cylinder 4. Running compression, snap throttle test
koer snap throttle 4.gif

KOER SNAP-THROTTLE-4.psdata
(713.73 KiB) Downloaded 592 times


So at cranking speeds cylinder 4 seems to have a compression issue compared to 3 but on a snap throttle test the peak pressures are almost identical for the two cylinders. Perhaps not just a simple case of poor compression?
Alan
Pico Staff Member
Pico Staff Member
 
Posts: 239
Joined: Thu May 25, 2006 8:02 am

Re: Lotus Esprit with low compression

Postby mapengo » Thu Mar 10, 2011 10:42 am

Hi Alan,

Interesting captures, haven't got around to looking at the compression waveforms in detail yet.

Looking at your snap throttle tests I can see you have compression issues coming off throttle.

I have manipulated your psdatas to illustrate what I am looking at.

Cheers

Doc...

Image

Edit.. Your screenshots look different to the psdata files I downloaded?

Are we singing from the same hymn sheet?

Out of interest (no info on Autodata or Tolerance) does this vehicle have hydraulic tappets / HVL?
mapengo
User
User
 
Posts: 16
Joined: Sat Aug 30, 2008 9:08 pm
Location: Warrington, Cheshire

Re: Lotus Esprit with low compression

Postby Alan » Thu Mar 10, 2011 9:12 pm

Edit.. Your screenshots look different to the psdata files I downloaded?

Are we singing from the same hymn sheet?


Its the same psdata file, but I did zoom in. Another possible difference is the units - I was set to imperial rather than metric. The compression does not drop below about 30psi.

Out of interest (no info on Autodata or Tolerance) does this vehicle have hydraulic tappets / HVL?


I am 90% certain they are solid (they have shims) but will check on Friday.
Alan
Pico Staff Member
Pico Staff Member
 
Posts: 239
Joined: Thu May 25, 2006 8:02 am

Re: Lotus Esprit with low compression

Postby mrblonde » Fri Mar 11, 2011 12:40 pm

hi nice to see some stuff like this very intersesting!
if i was checking i would like to see cranking intake and cranking ex pulses with cylinder id
I normally only use cranking current with spark id (timing compression) the wps lowers compression readings when used together maybe see cranking with out wps i know you have proved low comp just to see how it looks without wps? i havent done a lot of testing with cranking compression wave so would hope someone with more experience would show the finer points?
so running compressions are almost identical could we see intake running vacvum along with wps in cyl idle and wot and spark id 1
as other memeber mentiond no specs are available more info would help ex and intake opening closing times?,interesting stuff on intake side showing up? to my untrained eye look forward to seeing more
thanks..
mrblonde
Newbie
 
Posts: 8
Joined: Thu Mar 10, 2011 2:00 pm

Next

Return to Case studies

Who is online

Users browsing this forum: No registered users and 1 guest