Examining Chrysler 3.3 Engines For Broken Flex Plates.

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Examining Chrysler 3.3 Engines For Broken Flex Plates.

Postby Autonerdz » Sat Nov 23, 2002 1:00 am

When using the ADC 212/3 in an automotive application, one of the most powerful features is the ability to capture long runs of data and then zooming in to examine the details.

The Chrysler 3.3 engine is noted for breaking the flex plate around the crankshaft hub. This allows the flex plate to shift throwing the crank sensor output out of sync with the cam sensor. The result is a disruption of the spark and injection. This shifting can occur intermittently and can be related to engine load. There is usually no odd noise associated with this and the best way to identify the issue is with a scope. The short pulse duration is a challenge for many scopes as the sample rate breaks down when trying to capture a long run of this signal.

The ADC 212/3 can capture a full second (over 12 engine revolutions of these signals at idle) allowing the technician a MUCH bettter chance of seeing this shift in cam and crank signal synchronization.

Here is an example of good cam and crank syncronization:

Image

A 10x zoom in on the capture allows a close examination of each pulse:

Image
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3.3 broken flexplate

Postby Guest » Sat Nov 23, 2002 2:00 am

Even when the flexplate is broken the DaimlerChrysler scan tool (DRB3) will still indicate that the cam and crank are still in synch. The labscope is the only wasy to find this problem
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3.3 Crank And Cam

Postby Autonerdz » Sat Nov 23, 2002 2:19 am

Thank you for mentioning that. Absolutely true. The scanner will not reveal this issue. This procedure is the same for the 3.5 belt driven engine as well. The signals are the same.

:shock:
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Postby Carl Grotti » Sat Nov 23, 2002 5:09 am

Hi Tom,

You make a good point about the relationship in the two signals. We can see this in longer runs. However, it should also be pointed out that the flexplate can spin and land on the same spot as a good signal and stay there. I think it's important to say this because it has happened. I hope none of you ever experience this. We look at our relationships and all looks ok. It can't be that any Cam/Crank components have shifted. Yes it can. Be carefull of a wave telling the whole story. :wink:

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Flex Plate Picture

Postby Autonerdz » Sat Nov 23, 2002 9:40 pm

Hi Carl,

Good point. Just because the relationship is ok does not mean that the flex plate is not broken. Sometimes these can be broken and be jammed into a normal position. They will eventially slip and then may go back to the original position and remain there for a time. Of course, loading the engine will stress the break and it will then be more likely to shift.

I'm sure you have seen this but, for those who would like to see the actual part, I have a picture:

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Tom..nice to see you bud

Postby Doug Montgomery » Fri Nov 29, 2002 3:16 pm

I have to agree with Tom. I have fixed MANY a 3.3 with a broke flexplate with a scope.

I had one case that went to three dealerships until I helped a tech over the phone look at it.

The Chrysler data pids Cam and Crank Detected and in sync are not worth the code it took to put them in the PCM/DRBIII
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could it cause a vibration

Postby letsgododge » Wed Oct 26, 2005 1:18 am

Hi,I presently own a 2001 dodge caravan with a 3.8 lit motor AWD .I am having a problem with a engine vibration that starts out at aprox 1800 RPM then goes to 2200 RPM .it like a partis vibrating and goes right through the complete car .its worse under load.It have been to about 6 dealers ,

In my opinion there are two vibrations in my vehicle ,one is engine related and one is driveline related .
it has had 2 sets of tires put on,I set of rims ,8 drive sharts ,(2 front)4 rear and 2 front to back,.
I feel at certain speeds its from the engine and the driveline transmits it to the body.(it feels like a miss)when it goes into lock up and it seems to cut out as you drive it .It has not shown up on the computer (check eng Light ) or the DRB.
Would you think the flex plate is busted.I was thinking there is a issue with the torque converter,at its stall speed and it just happens to create some of these issues.

thanks for all your help

letsgoseadoo@sympatico.ca
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Postby jugle » Thu Dec 29, 2005 3:13 pm

seems that this topic is too old to have a reply, but i'll try. so my chryser gr voyager '94 AWD is having problem like you described- when driving it seems like one spark plug suddenly misses one cicle (sometimes more)and car at those moments twitches. but thats not all- i am using LPG (propane- butane) on my car so at those moments it backfires and there is explosion in intake manifold (nothing serious except noise). but all of that happens mainly when accelerating even slowly or driving at steady speed. obd swows nothing and no problems discovered by scantool. i went to transmission repair shop but they said that thei have seen such broken plates, but that there is always noise coming from them, so they did not believe that it could be this problem. what do you think of this and shod there be noise from broken plate or not.
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Broken Flex Plates

Postby Autonerdz » Thu Dec 29, 2005 3:43 pm

The one shown here made no noise. They usually don't make any noise. The only way to identify the problem without disassembly is with a scope. The scanner PID on CKP/CMP sync is not reliable either.

Pico's new line of 3000 series automotive scopes are hundreds of times more powerful than the 212/3 unit used for the captures shown here. This enables you to get hundreds of engine revolutions on each screen with zoom levels of 2000x. When you combine this with a record session where each screen is saved to the hard drive, it makes finding problems like these a pleasure.
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Re: Examining Chrysler 3.3 Engines For Broken Flex Plates.

Postby chryslerguy » Wed Mar 30, 2011 6:30 pm

Here is an example of improper cam and crank synchronization due to a broken flex plate in a Chrysler 3.3L engine (flexfuel)
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