mikehayes

New 16V '87 engine, had the '84 starter from my old engine on it, worked fine for a while, then died. I bought a new (rebuilt) '87 starter, starts up fine now, but takes twice the time before it fires, and occasionally it will fire but die as soon as I let go of the starter. Once it is running, it runs perfectly with no incident. The starter is not slow and does not sound like it's struggling at all. I would suspect speed sensor adjustment, except that it runs perfectly otherwise. Any ideas?

V2Rocket

test the ignition switch?

Jfrahm

Use a spark checker to see if you have a good strong spark while cranking. Just using a plug is not good enough.

mikehayes

Replaced it at the time of engine swap.

mikehayes

Ok. I'll clean the makeshift ground for the ICM too.

marc abrams

Sounds like a weak fuel pump. Check your fuel pressure while cranking.

No Lag

T&T Racing

The starter on my 944 8v was replaced and the engine starts have experienced the same symptoms. The engine starts progressed to no start. When replacing the starter, there is a realignment of the starter gear with the ring gear on the flywheel. The re-engagement process creates metal filing chips. I am now investigating and pulled the speed and reference sensors.
There were metal filings attached to the bottom of both sensors. My assumption is that required gap has reduced to the point where the sensors do not function. Both sensors tested functional per Clark Garage procedure using ohm meter test only. I also tested each prong of the plug to ground on the metal portion of the sensor and there was no leakage.
I have not reinstalled the sensors, going on vacation for a few days.

mikehayes

Interesting. Please keep us updated once you do find your issue. I will pull my reference sensor just to make sure but I doubt this is my problem as I only experience it on cold starts.

mikehayes

Fuel pump is only a few years old. Had perfect pressure at the time of the engine swap this spring. I can check again, but I only get the issue on cold starts. Unless there's some reason the pump would function better with the vehicle hot?

mikehayes

This had occurred to me. Maybe the problem only happens on "cold" starts because it's been sitting for a while and had a chance to flood the cylinders. I'll pull the vacuum line. Is it possible for it to fail and not show a leak?

marc abrams

I mentioned this because I've seen fuel pumps slow to build pressure when cold but after started work perfectly. This happen to a friend of mine L98 TPI engine. And his fuel pump was only a year old.

No Lag

T&T Racing

Can you run the fuel pump without starting the engine? Check your fuel pressure after fuel pump has run and is shutoff during "x" period to determine if the fuel pressure leaks off. Could be a failed check valve at fuel pump outlet. See Clark's Garage for test procedure. Also test the engine water temperature sensor connected to DME. This sensor compensates AFR for cold starts. See Clark's Garage for test procedure.

mikehayes

Managed to get a few minutes to mess around with the car this weekend. Pulled the vacuum lines from the damper and regulator, no smell of fuel.

I suspected the 16V specific ignition control module, so I took a close look at that. To my surprise, the connector was missing its wire locking mechanism, and when I pulled the connector off, it had a small amount of water in it. I thought for sure this would be the problem. I cleaned the ground for the ICM, heated the connector with a heat gun to get any excess moisture out, made sure all the pins were clean, made a new wire clip, and re mounted it at a different angle further into the engine bay to avoid future water intrusion. Didn't solve the problem at all. I do feel better about it though haha.

I ran out of time, but I was able to verify that the problem does not occur due to the engine not being hot, but rather the car having sat for a significant period of time. I let it sit overnight, started it, took forever and coughed to life. Immediately killed it and restarted it, fired up immediately. So the fuel system not holding pressure certainly seems like a possibility. My next test will be to let it sit for a while and then jump the pins of the DME relay to run the pump before I start the car. If it starts right up, that'll pretty much confirm it's either the pump, check valve, or something else I'm not familiar with.

Edit: Did the S and NA use the same fuel pump? Is there any reason my 8V fuel system wouldn't be able to keep up with the 16V engine? I know the injectors require a different current but I don't know what that means in terms of fuel flow.