TheCorvetteKid

Hi everyone,

I'm still trying to diagnose this hard starting problem I've been having. I've been trying to do it step-by-step and slowly eliminate what it could be without spending money on stuff that doesn't need to be replaced.

I did a compression test, and all the numbers came back fine - all 180 to 190psi. I conducted a fuel system pressure test (at the fuel rail) and everything looked ok there too. So it's not low compression and it doesn't seem to be fuel related.

I finally got around to testing my TPS and Coolant Temp Sensor. And here's the numbers:

CTS: 2.07Kohms @73degF (ambiant) and 53% humidity

TPS: 0.49V@closed throttle position; 4.45V@W.O.T.

Do these numbers seem right to anyone out there? The car is a stock '89 L98 by the way.

The TPS number seems a little low, but within GM specs (0.54V+-0.08V); I have no idea if the coolant temp sensor is reading ok or not.

So if these number are OK, then it looks like it may be an ignition problem. Anyone know how to test an HEI coil for proper output?

Thanks in advance.

65Z01

The thermister value sounds ok, though I don't know the exact expected value at that temp.

The TPS is a little low, set it to .54-.65Vdc at base idle of 450rpm (with IAC pintel fully extended).

BTW, what trouble symptom are you checking?

TheCorvetteKid

When you say 'base idle' what do you mean? My car idles (when at operating temp) at like 700-750rpm. How would I get the rpm to drop to 450? And when you say IAC pintle fully extended, I have to ask the same question: what do you mean? I've never removed/inspected/installed an IAC other than what I've seen in the manual, so you'll have to walk me through your explanation.

I have a hard starting problem with my car when cold. It cranks for a LONG time, but evetually fires. It runs like crap for a second or so, then runs fine. When hot, the car cranks less than when cold, but still longer than I would like. I had my injectors replaced 2 years ago, so I don't think it's a leaky injector problem. I throught it was engine compression, but the compression test revealed all my cylinders where fine (180 to 190psi). I've inspected my injector fuses, and both look fine. I conducted a fuel system pressure test with a gauge attached to the fuel rail, and everything seemed OK. So I decided to check both my CTS and my TPS in accordance with the GM service manual. And while I agree that the CTS values I got look OK and the TPS values look low, according to the service manual, a high TPS voltage could cause this hard starting condition, not a low one.

I'm still stumped. I've even tried disconnecting my MAF and starting the car to see if that solved the problem, but it didn't. The only thing I haven't tested yet is my ignition system. I've set the timing to 6degBTDC and I'm sure that it's OK, but I don't know how to test the output from the coil.


[Modified by TheCorvetteKid, 10:53 PM 6/7/2003]

65Z01

There is a method on my site for setting base idle and TPS voltages.

Since you have an '89 L98 cold starting issues cannot be due to the 9th injector; but have you checked fuel pressure and verified that the fuel rail holds a prime after you turn on the ignition, before starting the engine?

You might also verify that the coolant temp sensor (the one under the TB) resistance changes with temp change. I don't know the exact values but resistance should drop as temp increases.

TheCorvetteKid

I'll check your site a little later today. Thanks. Hopefully it'll clear things up for me.

Yeah, I've run a fuel system pressure test and everything seemed OK. When the key was turned to 'ON' the pump primed the system for 2 seconds and I saw 45psi on the gauge. When the pump stopped, the pressure was 40psi and holding. When the engine was cranked over, the pressure was 45psi. Once the engine was idling, th pressure dropped to 38psi steady. I disconnected the fuel pressure regulator and the pressure jumped to 45psi, then back down to 38psi when reconnected. When the car was shut off, the pump ran again for 2 seconds priming the system to 45psi, then when it stopped it held at 40psi.

I thought that 38psi at idle was alittle low, but from everything I've read and seen, this is actually normal. I should probably mention, I don't have an adjustable fuel pressure regulator - my car is pretty much stock with the exception of a few usual things (K&N, cut MAF screens, 1.6 roller-tip rockers, and no frisbie).

I haven't tried that yet. But I will. I'm just finding it hard to find the time to get into the garage and work on the car.

Thanks for the tips. I'll check your site and see if adjusting the TPS voltage will make any difference. Someone suggested swapping out my ECM to see if it may be at fault. I have a new unit here still in the box. Maybe that'll do it.


[Modified by TheCorvetteKid, 9:03 AM 6/8/2003]

Ray Quayle

I notice you always mention setting the TPS at base idle with pintel fully extneded and wonder why. The important thing is to set the base idle with pintel fully extneded as you describe very well on you site. Once this is completed, plug the IAC back in, start 'er up and let it idle where the ECM wants it to. The IAC does not change the Throttle Position, only the bypass air. Heck, you can even set the TPS with engine off as long as ignition is on. As long as the adjusting screw has not been messed with since a minimum idle was done, there's no need to extend the IAC pintel to set the TPS voltage.