First Start Problems

[C3larke]

Hi,

I just got the engine reinstalled after a clutch job and am having some trouble getting it started.

The clutch pedal feel had suddenly changed and the clutch started slipping when I got on the power. Once I got it apart, I found the pressure plate spring was cracked!!! If you are ever considering re-using the pressure plate, I would recommend changing it.

Today I got the motor back in the car. I cranked it up, and now it is running really rough as if the timing is off. I can't figure out what's going on, ran perfectly before the clutch job. The only change I made was installing a lightweight Aasco flywheel. Here is a video of the car running:

https://www.youtube.com/watch?v=1cifKyXYEM8&feature=youtu.be

Sounds as if it's running normally at first, then it drifts off and starts to backfire. Opening the throttle just seems to bog it down.

Any ideas as to what might be causing this?

Thank you,

Chris

[C3larke]

Forgot to mention, the car is a 1985 Carrera 3.2.

[cabmandone]

Is your CHT wire tightly connected? I'd double check it. I took my engine out a while back and had bumped the CHT connector just enough to make it loose and my car ran like crap.

[C3larke]

That's a good idea, this rough running does seem like a possible lack of CHT sensor. Also strange since it ran well for a couple of seconds before drifting off into roughness and backfiring.

I believe the CHT connector is secure, but I will double check it. I will also measure the resistance of the sensor to make sure it is reading correctly.

Thank you for the input,

Chris

[cabmandone]

When I bumped mine and made it loose, the car would run like crap and would cough and backfire and finally die if I put it in gear. Hopefully that'll be your problem.

[C3larke]

Well it looks like it is not the CHT sensor. I confirmed the connector is secure and also checked the resistance on the sensor and found it was about 2500 ohms which seems about right. 1400-3600 is 60-85 degrees per the Bentley manual.

I got suspicious that I may have set the gap incorrectly on the crank speed sensor, so I checked that as well. I put a shim on the tip of the sensor and reset the gap three times. No luck! Still getting the super rough running and backfiring. Looks like I had it set correctly after all.

Finally, I pulled one spark plug on each side. They both looked about the same, slightly brown. I don't think the plugs are an issue as it was running well when I started the clutch project.

The only thing I changed (that I know of) is the flywheel. The new Aasco flywheel had a ring of teeth and a set screw for the speed and position sensors and I have every reason to believe these are the same as the old flywheel.

Any other ideas as to what could cause this?

Thank you,

Chris

[yelcab1]

There are two ring gears on a 3.2 in the same vicinity. One for the starter to engage and turn the engine, the other is for the TDC sensor to sense the engine revolution. Did you get both in, correctly?

There are 3 connectors on the left hand side, top of the engine. Two of them have the same identical connector. Did you make sure not to swap them?

Did you check for any possible vacuum leaks in the various hoses?

Ground wires are all in? The bottom one near the transmission, and the wire bundle at the upper left hand side of the engine?

Idle valve connector in? MAF sensor connector in place?

Throttle position sensor in place?

There is a small air hose at the front of the air box, hard to see, is that in place?

[C3larke]

Both ring gears are in correctly to my knowledge. The flywheel gear for the speed sensor is integral to the flywheel and I installed the pressure plate ring gear on top of the pressure plate.

The CHT, speed and position sensor connectors are all in place. I tried switching the speed and position connectors, but the engine will not start at all. It only runs with them positioned this way.

The ground wires on the left side of the manifold are connected and the ground strap at the front of the transmission is connected. I remember now that when I was lowering the engine I had forgotten to disconnect the ground wires from the intake manifold. I tugged on them a little bit before I realized it. The connectors all appear fine where they are bolted on the manifold, but it is possible I may have damaged a wire under the shielding. Could this be a potential problem, and if so how can I test the ground wires?

The idle, air flow, and throttle position sensor are all connected. I verified the idle control circuit is working by jumping the two pins for setting the idle speed. This caused the idle to slow considerably and nearly stalled the engine.

I have not looked over the vacuum lines yet, will check on that after work tonight.

Thanks for all the suggestions,

Chris

[cabmandone]

It seems like something obvious is being missed here. Is the distributor cap on squarely and secure? Coil wire pressed on coil and distributor? 6 pin connector on the strut bar connected securely? I would go back and check all of your connections. If you're starting then the speed and reference sensors are working. If your vac lines were the problem I think you'd just have really low idle. I'll scratch my head on this some more but it seems like there are only a few possibilities since nothing was done but changing the flywheel. Your car almost sounds like you have plug wires crossed or something but you say you didn't do anything but the flywheel so that can't be it.

[cabmandone]

IIRC, there is an engine harness on the driver side that gets unplugged. I'd unplug it and look at all the female pins to make sure you didn't have one pushed back inside the connector or something weird.

[Targalid]

John Walker reported a similar problem with a replacement flywheel. It turned out, if you check his thread, that the flywheel material no longer acted correctly with the magnetic pickup that gives engine speed to the ECU. I can't find it right now but he finally tracked it down to metallurgy changes in the flywheel.

[C3larke]

I will check the connectors and make sure all the pins look good.

I sure hope it is not the new flywheel. I will see if I can find the John's thread. Do I need an oscilloscope to check the signal from the speed and reference sensors?

[scarceller]

Get it running and check the timing at idle, you should be around 0-5 deg at idle fully warm. During cold start (warm up phase) you can be in the 10-20deg area. But you should not drift on timing at all once warm. If the timing is correct and not drifting then your issue is likely fuel.

If you tugged on those ground wires at that main ground screw they all need to be checked. Those provide all the grounds for the sensors as well as the DME. One of those brown wires provides the ground for the CHT sensor, if it's broken the DME will think the motor is stone cold at all times. She'd run very rich.

[C3larke]

Just got it figured out!!!

I tracked down the thread started by John Walker on the bad flywheel screw preventing the crank position sensor from getting a reading. In his case, the screw was stainless steel and would not excite the sensor. I also found another thread in which someone suggested testing the crank speed and position sensors by jumping pins 1 and 2 on their connectors with a LED test light. I tried that and found one of the sensors made the light flash like crazy and the other did nothing at all. That led me to believe I had a problem with my reference screw.

I went under the car and got a buddy to crank the motor around until I could see the reference screw in the small hole on the bottom of the bell housing. The screw took a magnet, not stainless steel. I then measured the protrusion of the screw on my original flywheel and compared. The screw in the new flywheel only stuck out 1/8 inch while the screw in my old flywheel measured 3/16. The new flywheel has a different thread size, so I went down to the hardware store and picked up a new screw that was slightly longer. Put it in and measured the protrusion at 3/16 of an inch just like the old flywheel.

With the new screw in place, I cranked the engine over once by hand at the pulley to make sure my new screw didn't hit the sensor. Then fired up the car to the sweet purring sound I remembered before tackling this clutch project. I'm back in business!!!

Thank you for all the help, don't know how I ever would have figured that out without you guys.

Chris

[cabmandone]

One word.
Sweeeeeeeeeeeeeeeeeeeeet.

This would seem to show that the car will run with a malfunctioning reference senor but run poorly. I thought if either one didn't work properly the car would not run at all.

[scarceller]

Nice find and quickly done!
I'll remember this issue for sure!

Thanks for reporting the solution.

[yelcab1]

This confirms my rule number 1 in DIY. If you mess with it, and it does not work anymore, it is directly related to something you did.

In this case, you replaced the flywheel and it does not fly anymore, then it is your flywheel that is the problem. Look no further.

Great find.

[C3larke]

After a couple of days of driving everything is still working as it should. The clutch pedal is WAY firmer than I remember it, so the old pressure plate must have been tired for a long time before it let go completely. I forgot how fast the car was after a month of driving with a slipping clutch!

I am extremely relieved that I got it sorted out with such an easy fix. I wrote to the flywheel manufacturer to alert them to my problem. Hopefully they will address this issue before this happens to anyone else.

Whenever replacing a flywheel on a 3.2, I would recommend checking the speed AND reference sensor gaps on the old flywheel and verifying the gaps are correct once the new flywheel is installed. It only takes a second to check and set the clearance when the engine is out, and I can attest that it could save a lot of trouble once the engine is installed. Also couldn't hurt to take a magnet and make sure it sticks to the reference screw in the new flywheel.

Thanks again for the help!

Chris