Cold Start Issue When Outside Temp is <35 Degrees
01-15-2012, 08:56 AM
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Car: 88 IROC-Z T-Top car with Bose
Engine: L98 5.7
Transmission: 700R4
Axle/Gears: 9 Bolt with 3.27's
Cold Start Issue When Outside Temp is <35 Degrees
Hello all,
I'm having a cold start issue with my 1988 IROC-Z. The car is pretty much stock except for a modified airbox with K & N filters. When the outide temp is below 35 degrees, it starts, but after about a minute when the idle comes down slightly, it starts idling rough and smells rich at the exhaust. If you try to give it gas while its idling in this state, the motor hesitates. Once the car warms up, it acts pretty normal except for a miss occasionally at idle. If the outside temp is above 40, it starts and runs fine.
When I first bought the car, it had a similar issue that was the mass air sensor. The car wouldn't even run until completely warmed up. That was diagnosed by disconnecting the MAF and it started fine. I did that seeing if it would make a difference this time and the car acted the same.
I would think it could be injectors, but I just replaced the set that was in there about 2 years ago with Bosch III's. Is it possible it could be injectors again?
I still have the cold start injector, but I would think if this was bad, it wouldn't run at all, not smell rich.
I think this and the intermittent miss are related, but I am not sure how.
The car is outside so diagnosis time is limited since its 20 degrees with a high of 30 today.
Thanks for any help in advance!
I'm having a cold start issue with my 1988 IROC-Z. The car is pretty much stock except for a modified airbox with K & N filters. When the outide temp is below 35 degrees, it starts, but after about a minute when the idle comes down slightly, it starts idling rough and smells rich at the exhaust. If you try to give it gas while its idling in this state, the motor hesitates. Once the car warms up, it acts pretty normal except for a miss occasionally at idle. If the outside temp is above 40, it starts and runs fine.
When I first bought the car, it had a similar issue that was the mass air sensor. The car wouldn't even run until completely warmed up. That was diagnosed by disconnecting the MAF and it started fine. I did that seeing if it would make a difference this time and the car acted the same.
I would think it could be injectors, but I just replaced the set that was in there about 2 years ago with Bosch III's. Is it possible it could be injectors again?
I still have the cold start injector, but I would think if this was bad, it wouldn't run at all, not smell rich.
I think this and the intermittent miss are related, but I am not sure how.
The car is outside so diagnosis time is limited since its 20 degrees with a high of 30 today.
Thanks for any help in advance!
01-15-2012, 09:56 AM
#2
Re: Cold Start Issue When Outside Temp is <35 Degrees
What troubleshooting have you done so far?
Do you have any sparkplugs that look abnormal ?
A plug with a cracked insulator, a cracked internal resistor, or a loose screw-on tip can cause intermittent misfires.
A misfire will throw off your O2 ability to provide proper feedback for fuel delivery.
If you have a fuel delivery problem, then start your checks with the fuel pressure, and check your CTS output cold and hot. Your injectors are pretty new, but you can't rule them out, so I would check them too.
Keep in mind that a lean misfire will also cause a raw fuel smell in the exhaust along with rough running and hesitation when you hit the gas.
Do you have any sparkplugs that look abnormal ?
A plug with a cracked insulator, a cracked internal resistor, or a loose screw-on tip can cause intermittent misfires.
A misfire will throw off your O2 ability to provide proper feedback for fuel delivery.
If you have a fuel delivery problem, then start your checks with the fuel pressure, and check your CTS output cold and hot. Your injectors are pretty new, but you can't rule them out, so I would check them too.
Keep in mind that a lean misfire will also cause a raw fuel smell in the exhaust along with rough running and hesitation when you hit the gas.
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