Cold Start Help, Not Starting On All Cylinders ?

[CARRERIC]

Need help troubleshooting cold start. My engine (2.7L) is not running on all cylinders on start up. It will run on all cylimders a couple minutes later. I have replaced the following with new parts:

fuel filter
fuel injectors
warmup regulator
cold start valve
thermo time switch
fuel pump

Any thoughts?

Tanks
Eric

[cowtown]

Wow. That's a lot of $tuff you replaced, mostly on the fuel side. What prompted it - was your pressure or delivery too low? How's your control pressure cold and hot?

Have you checked out the ignition? Verify spark, plugs, cap, wires, etc. Maybe you have a heat-related spark or grounding problem.

How did you determine it's not running on all cylinders? Is it a problem with one specific cylinder, or just rough running in general?

Finally, are you using your hand throttle lever on cold starts, and have you verified the linkage is working correctly?

I think we're going to need some more information on this one

[surflvr911sc]

I agree, trace ignition back. Plugs, cap/rotor, wires. Try one at a time in that order and see if it leads anywhere.

[CARRERIC]

Thanks guys. I replaced most of those items because of age and process of elimination for other problems. I just installed new spark plug wires last month, the cap, rotor and plugs have about 5K on them. The car runs good after the initial start up. It's the first minute or two when you use the hand throttle and engine pops a couple of times until it reaches 2K. But in this time the car doesn't appear to be running on all the cylinder. I just bought a fuel pressure guage and will try this weekend. I can't figure it out!?!

[cowtown]

Well it sounds like it's during the warm-up cycle, when the heater element is warming up the WUR. The control pressure test should tell you a bunch about this. If it's too high, you're lean, too low, you're rich.

If it is the cold control pressure, there is an adjustment mod you can make to the WUR to get the cold control pressure back in spec. It doesn't affect hot control pressure though. BUT, this really shouldn't be necessary with a brand new WUR....

Let us know what you find.

[CARRERIC]

Is it possible that a pulled head stud could cause this if I am loosing slight compression from a cylinder. No popping.

Eric

[mb911]

I doubt it would be the head stud unless you notice a lot of oil build up on your garge floor. I have a 3.0 in my 77 911 and just replaced the WUR. The one I put in causes my enigne to start real rich and then leans out and runs fine. It sounds very similar to what you describe. The other possibility is that when the engine is cold it may not have the compression that it should and would cause for weak running engine. As the engine warms up the tolerances become tighter and you get a smoother running engine. That is worst case. I would check and recheck fuel pressures and all ignition components. Ohm out your spark plug wire caps and wires them selves. That may at very least rule something out.

Good luck
Ben

[Early_S_Man]

Normally, compression tests are done on a hot engine ... but I suggest doing a check on your engine cold so as to duplicate the cold start conditions where you seem to have this problem. A leaking cylinder due to bad/pulled stud could indeed generate more compression after warming up a bit.

Does this problem seem less significant if the restart is on a warm engine?

Is there any noticeable 'spitting' sound like an exhaust leak when the engine is first started and the miss is present?

[azasadny]

Carreric,

Your problem sounds like mine. I finally took it to my mechanic and he told me the plugs were gapped too wide. I gapped the plugs according to the PermaTune specs and the car ran great, but it was almost impossible to start and ran horrible until warmed up. I also had some backfires. Now, it's been two weeks and everything is great, that's all it took...

[CARRERIC]

Warren, Yes the problem seems less significant when the engine is warm. No spetting just the typical few pops when it's rich on coldstart.

Art, I'm going to replace the plugs tomorrow. What is the appropriate gap?

Thanks
Eric

[mb911]

I think Porsche specs are .028 but permatune runs .065 and same with MSD and ETC. Hope you have good luck.

Ben

[azasadny]

I had my plugs gapped at .060 and that caused all kinds of cold start problems! They are now set at .035 and all's well. Car starts like a dream and runs great!!!