M42 hard to start, won't stay running

[Gooch]

Hey guys, just want to pick a few brains here.

Yesterday I went to start my car to go take my MCAT an hour away, and my car wouldn't start. I could get it started by giving it a little gas while cranking, but then it would die out. Then I could get it running for a little bit and it had a terrible idle, then it would die out. If I held the throttle down it would stay running, as soon as I let off the idle would bounce around and it would die.

This has happened maybe once or twice before but I chalked it up to needing to clean my ICV. When it happened before, it was hard to start, I got it started, gave it a little gas and all was fine after a few brief seconds. Also, very intermittently and rarely the car's idle will fluctuate quite a bit like sitting at a red light. Twice the car stalled sitting at a red light due to the erratic idle.

I tried removing the ICV and cleaning it, put it back in and the car idles terribly. Does anyone have any ideas? Fuel pump and fuel filter are new. Other than that I haven't done anything to the engine or anything since I got it a few years ago. I'm up in Scranton, PA and I'm trying to get home for the summer. I have a friend who is kind enough to bring me an ICV and an AFM out of another M42 car tomorrow. But if worst comes to worst I may have to get it towed home. I'd really like to avoid this, so if anyone has any ideas, please let me hear them! Thanks in advance.

[///M42 sport]

might be your ignition coils. happened to me once before. Also check your plug wires and spark plugs. You could go either OEM or with the COP kit for replacing the coils.

BTW Im a 4th year med student. and it doesnt get any easier lol.

[Gooch]

Fourth year, wow that's impressive man. Keep it up! Where do you go?

I actually managed to get home today. I swapped in my friend's ICV first, nothing changed, still a terrible fluctuating idle and the car would die. Then I swapped in his AFM and my idle was fixed. I turned the car off and on again and it seemed to be fine. So I took it for a short little drive and everything was fine.

However, after I loaded all my stuff up and got onto the highway to come home, there was an intermittant pulse or surge where I'd lose power for a second and then it would be fine again. Then maybe 15 minutes into the drive on the highway I lost power and pulled over, RPMs dropped, so I took my foot off the throttle and got onto the shoulder. I attempted to give it more gas and everything seemed okay, so I got back on the highway.

Then it would give me the pulse/surge thing a few more times then about 45 minutes into the drive the car lost all power and stalled. So I pulled over and had a hard time starting the car again. After I got it started, everything was perfectly fine the rest of the trip. Not a single pulse/surge, hiccup or anything. WTF?! Does anyone have any ideas? Gonna have a friend come over and we're going to ohm some sensors and see if we can come to a conclusion. Any help is appreciated.

[3bvert]

not in order
crank sensor, cam sensor, throttle position sensor, gas cap

did you notice if it happens at a particular speed when on the hiway ( or rpm) could be the tps
any speed or rpm crank or cam or gas cap

I bring these up because I had a similar problem, replaced the crank and cam sensor ( out of another car) cleaned the icv, problem gone for a few hundred miles then problem continued
nothing showed on the stop test
someone else suggested the gas cap, take it off, drive it see if it makes a diff, for me, did not
replaced throttle postion sensor, done

in searches youll find the resistance values of the crank and cam sensors

[Gooch]

Thank you for the reply, I really appreciate it.

For now I'm going to tackle "the mess under the intake" and see what happens. Then I'm going to start taking a closer look at the sensors and everything. I'll post up my findings after I get my parts from Blunt and after I get back from York this weekend.

[3bvert]

yep yep yep, the mess under the intake is a great place to start and that snake pit could be where your getting bit

[KenC]

Fuel pressure regulator could also be the culprit.

[Kershaw]

the TPS is also very easy to check.

i was having problems with my car starting and then dying, and it ended up being the TPS. it took forever to get the car started. and then it would die really easily. the car would start up instantly if i unplugged the afm though, because then the dme would dump fuel into the engine.

the TPS is directly under the throttle body. unplug the wire to see the connectors. set your multimeter to continuity, and check for continuity across prongs. i believe its the last 2? not sure on that. just try all the different combinations. haha.

[jlevie]

Not mentioned in any of this is the possibility of intake leaks, which is a prime cause of starting and idle problems. A smoke test is the only way to loacte all intake leaks.

[///M42 sport]

I only say check the coils bc I had similar problems to you. I got a really bad idle suddenly and ran like crap. I had to give it gas or car would at idle. Replaced all hoses, ICV, TPS, ordered coolant sensor. In the end it was a bad coil.

[Gooch]

Okay, so I finally got everything back together and go to start it and I got nothing. The AFM and ICV were replaced with units from a running car. The car will crank but the fuel pump is not kicking on.

Went through the sensors and coils as per the Bentley.

Coils are fine.
TPS is fine
Camshaft sensor is fine.
Crankshaft sensor I get nothing on the multimeter.

I know that a faulty crankshaft sensor will not allow the car to start, but the question is will a faulty crankshaft sensor disable the fuel pump from turning on when the key is on? I tried jumping the fuel pump as per the Bentley and it does turn on when the key is on, so it's not a fuel pump issue. (It and the fuel filter were recently replaced without issue).

[jlevie]

The fuel pump is controlled by the DME. If it doesn't see timing data from a rotating engine the relay won't be turned on. Replace the CPS.

[Gooch]

Thanks Jim, I'll go ahead and do that. I was also just going to edit my post and say that the stomp test indicates 1-4-4-4, no fault codes. But I guess that's irrelevant now.

[Gooch]

Thank you to everyone for the help and suggestions. It was indeed the crank position sensor. If you search up Cobra Jet's no start thread on m42 club, it goes through a ton of no-start scenarios and was a huge help.

From what I understand this is a rather frequent occurrence on the M42 and the ECU will not throw a fault code (but it is supposed to). So if you have a no-start issue and you're chasing your tail, check the crank sensor!

Thanks again, guys.