1989 Corvette, Cranks for like 15 seconds when cold before it starts

**Superc63** · 10-21-10, 07:08 PM

Hi,

So, for the past couple months, every morning when I would fire up the Vette, I'd have to crank it for a good 15s before it'd start. I would usually break the crank attempts up into like 10 1.5 to 2 second attempts before it would fire up.

After that, entire rest of the...starting would be fine. It would fire within like 1 second for the rest of the day.

Following morning, problem would return.

After reading lots of posts and stuff, I figured out what my issue was and thought it may be helpful to others. It was my Intake Air Temp sensor. It is located on the bottom of the inlet plenum a few inches ahead of the distributor. It is like right next to the fuel pressure regulator.

Anyhow, I unplugged it and fired the car up. It started immediately. Granted, it is like 60 degrees out...but still. I am confident the problem is isolated. I will likely look into buying one of those remote relocation kits for the sensor.

Cheers,
Chris

**boomdriver** · 10-21-10, 07:34 PM

Originally Posted by Superc63

Hi,

So, for the past couple months, every morning when I would fire up the Vette, I'd have to crank it for a good 15s before it'd start. I would usually break the crank attempts up into like 10 1.5 to 2 second attempts before it would fire up.

After that, entire rest of the...starting would be fine. It would fire within like 1 second for the rest of the day.

Following morning, problem would return.

After reading lots of posts and stuff, I figured out what my issue was and thought it may be helpful to others. It was my Intake Air Temp sensor. It is located on the bottom of the inlet plenum a few inches ahead of the distributor. It is like right next to the fuel pressure regulator.

Anyhow, I unplugged it and fired the car up. It started immediately. Granted, it is like 60 degrees out...but still. I am confident the problem is isolated. I will likely look into buying one of those remote relocation kits for the sensor.

Cheers,
Chris

Interesting....
I would never have thought that the IAT would have any effect on cold start.
Past situations like this were always associated with the fuel pump relay. When cold, if the relay is bad, the motor must build around 4-6lbs (+/-) oil pressure for the oil pressure switch to close and allow fuel pump operation. The IAT is the same as the water temp sensor in the front of the intake manifold under the throttle body..

**Superc63** · 10-21-10, 07:49 PM

Hmph, I wasn't familiar with the fuel pump relay thing...but I could/can hear the pump come on as soon as I put the key to on...prior to cranking.

Also, if the fuel pump relay was messed up...it would do that every time...not just at cold starts.

**aklim** · 10-22-10, 11:41 AM

Originally Posted by boomdriver

Interesting....
I would never have thought that the IAT would have any effect on cold start.
Past situations like this were always associated with the fuel pump relay. When cold, if the relay is bad, the motor must build around 4-6lbs (+/-) oil pressure for the oil pressure switch to close and allow fuel pump operation. The IAT is the same as the water temp sensor in the front of the intake manifold under the throttle body..

It might from the standpoint that it changes enrichment of the fuel curves. By unplugging it, he is sending an infinite resistance reading to the ECM and it is dumping a lot more fuel.

Unplugging is a way to diagnose something. It is an idiot's cure to a problem when they are unable and/or unwilling to take it any further.

**aklim** · 10-22-10, 11:43 AM

Originally Posted by Superc63

Anyhow, I unplugged it and fired the car up. It started immediately. Granted, it is like 60 degrees out...but still. I am confident the problem is isolated. I will likely look into buying one of those remote relocation kits for the sensor.

Cheers,
Chris

Not always. The question is why it does that? Plug in your scanner and see what the IAT temp is. If it is correct, all you are doing is lying to the PCM so it does something else to compensate for another problem. Maybe you have lower fuel pressure. Maybe you have clogged injectors.

**Superc63** · 10-24-10, 07:37 PM

So,

I bought a new IAT sensor at Pep Boys for 13 bucks. I plugged it in in place of the original one and problem solved, car starts immediately now under both hot and cold conditions.

I did not want to take apart the intake to replace the stock sensor, so I just put some extension wires into the harness and put the replacement sensor in front of the radiator near the driver side headlight. Works like a champ.

Side note, I notice no performance difference...just way better cold starting.

Cheers,
Chris

**Stump** · 11-09-12, 01:43 PM

My 1989 vette is doing the same as yours was doing. But when I call the parts store they were telling me that intake air temp senor was $40.00 some dollars. If you could give the part no# off of the part that you replace I would dance at your next wedding lol lol lol

**boomdriver** · 11-09-12, 03:30 PM

The IAC sensor is the same as the eng coolant sensor...one may be listed cheaper then the other...

**Stump** · 11-13-12, 12:26 PM

Were is this IAC sensor located at? I can't find it on my 1989 vette

**Schrade** · 11-13-12, 03:49 PM

I'm pretty sure that the IAC and the CTS are different sensors.

IAC is on the throttle body. Can't remember where the coolant temp sensor is on L98...

**steveb01z06** · 11-13-12, 08:22 PM

It sounds like you may have fixed it, but this reminds me of when they discovered that the backs of intake valves would carbon-up and first starts would take abnormally long because the carbon would absorb the first fuel pulses and lean the mixture in the combustion chamber.

I also remember that there used to be a separate cold start injector but at some point they just reprogrammed the ECM to give more fuel during cold starts.

**Stump** · 11-19-12, 01:03 PM

Superc63,
You were right. I replace the sensor that was located under the manifold in front of the distributor but it was hard to get to, but I got it. And it fixed the cold starting problem. My fuel pressure was at 51 psi. Thanks you again for saving me alot of money and time.

**WhalePirot** · 11-29-12, 10:29 PM

The cold start injector was used for about the first two years of TPI.

I'd have looked at the fuel pressure (shraeder valve) expecting leak down overnight or other lengthy cool down periods. Leaky injectors are a prime suspect and the FSM specifies a pressure /versus time spec..

The ECM runs the fuel pump for 5 seconds on startup, then requires oil pressure to keep it going. Usually, you can hear it; not always. The relays, now Chinese made, have had issues but are identical to others on the car, for quick testing. There's a mod to alter them slightly (capacitor), to greatly lessen arcing when the mechanical points close/open. Some afgtermarket relays incorporate this 'mod'. I have fixed relays with a file, when they got sticky due to wear or weird erosion patterns that kinda formed a hook on the contact points.

Glad your Vettes are fixed ad hope it lasts.