BHCfarkas

Hello friends! Have a bit of a head scratcher for everyone.

1990 C2 Cab that was in for a bit of much needed maintenance for a buddy's father-in-law. Received a whole top end re-seal, Alu valve covers, clutch/flywheel, valve adjustment, ignition coils, and spark plugs.

Engine out/in procedure that went without issue(I've done this many times), however, go to fire it up and it starts immediately first crank but also dies immediately. Fine, no problem, just need to diagnose a couple common things. Checked every single fuse and DME relay was first suspect- was replaced immediately but no success. Decided to jumper the fuel pump and DME manually with no luck. Tested the ignition coils, distributors, and double checked plug wire routing- all good. Read that the Engine Speed Sensor can cause an issue if not within 1mm of the flywheel ring gear- adjusted that and no luck. Suspected the ISV and cleaned it really good, checked voltage and operation- seems good. Also tested the sweeping voltage of the AFM with a D battery- no odd drops in the sweep of the internal potentiometer that the flap works, so I can only assume it's getting a good reading. Tried un-plugging the O2 sensor- no luck. Double checked every single connection in the engine harness is getting good switched voltage and there are no vacuum lines disconnected. Tested the idle micro switch- functioning as it should. Only thing I can say is, at one point the battery in the car COMPLETELY died, so I'm wondering if maybe that caused some kinda issue with the security system?

The best I can get out of the motor is that if I crank the engine and hold the throttle wide open, it'll rev up and stay alive if you bat the throttle heavily, however, won't idle to save it's life. I'm completely stumped and this isn't something that happens for me, often. Of course, this is a pre-CEL car as well, so I can't read out any possible codes.

Is this something a Hammer tool could help assist me? Does someone have a spare DME or Hammer tool they'd lend me? Any ideas of things to test or check?

Thanks in advance,

Andrew Farkas

Rocket Rob

You have checked the electrical side. Do you know you are getting fuel pressure? Do you hear the fuel pump run?

BHCfarkas

Yes, pump is running and I confirmed that by giving it power with jumpers in place of the DME relay. Fuel pressure is good, injectors are all getting fuel.

Rocket Rob

A couple other ideas

1) What's the voltage of your battery? Did you remember the ground strap between the starter and the bottom of the car? Can you measure the voltage when it cranks and is running? Is your alternator working?
2) Did you remember to connect the connector to the AFM? I've missed it during an engine install. Its not easy to see once the engine is in.
3) When it does start, does it sound likes all 6 cylinders are firing?

Lastly, a Scantool would be really helpful. Are there any 964 owners nearby with one?

18T_BT

How old are the plug wires? Unplug the coil one at a time and see if she fires up.

BHCfarkas

I was really hoping someone nearby might see this thread and offer a helping hand with a hammer tool.

I have checked the battery since charging and it holds a solid 11.5-11.8 with no load. I've gone as far as using jumpers from another battery in the event that the battery might not be providing enough voltage. It's got a strong crank and it doesn't appear to be battery specific related. I haven't checked to see if the alternator is pulling a charge, but that's probably not a bad idea to check. We definitely didn't forget about the ground strap near the starter, but I suppose it's possible it's not getting a good solid ground. It is a bit of a PITA to reach it lol. Now that I think of it, I can't really recall any other ground straps other than the one next to the starter and the one that connects the ignition components. Are there any others in the engine bay that I might look for?

When I do use the throttle heavily, it does sound like an otherwise healthy motor running on all 6 cylinders.. it just wants to die immediately if I don't touch the throttle- Doesn't even attempt to idle.

I've had the AFM in and out a number of times, between testing the unit itself and double checking connections and testing plugs, so I'm certain that it's plugged in.

Plug wires appear to be in good health, but I'll admit, we haven't checked the resistance between the ends from each cap to the plugs. Cap and rotor were toast, and we replaced both the coils for good measure, but not the wires. Ignition control modules were swapped to see if anything might change, but both test good. We get the same results if we unplug one lead of each distributor.

dlpalumbo

If you get desperate for a scantool, I have one loaded on a small Acer notebook. I have a Hammer clone, so I dont use the scantool any longer.

One thought though, could the secondary manifold butterfly (cant recall correct term. The 1 that opens ~ 5k rpm) be open? Or the WOT switch be engaged?

PM me if you want scantool. I'll see if it still boots.

Dan

greg1990964

Thanks for the wheel.
Sounds like you are getting spark, but have you pulled a wire and watched it arc as you turn it over? Sounds like a fuel distribution problem. Something must be reversed. I remember installing a motor and the colors on the connections looked right compared to the other 964 I have here, but they didn't work on the other car, they only work reversed. Must be something stupid. Sure you will figure it out.

justin-in-athens

Vacuum related maybe? Check main crankcase breather hose.

jeanhules

I was having similar issues after changing out my FPR and injectors. I put everything back together and it would start up quickly, then die. It was a puzzler to my too so I gave up and trailered it to a local Porsche shop. It ended up being the air flow sensor boot. Thankfully an easy fix.

prschmn

I'm voting you check for vacuum leaks too----that will absolutely give that scenario

Derek911

I always look to the battery. These cars don't like a weak battery. For some reason they can crank up, but have a hard time at idle. Will it stay running at higher rpm's?

tjb616

That was my first thought. I would check the MAF as well.