Tbi rough cold starts

[JPVortex]

Hi everyone I have a 94 k1500 with a 5.7 tbi.

Every cold start until the engine warms up it runs not good at all. It stumbles and has a obvious misfire with a pop from the exhaust.

Has new cap, rotor, temp sensor, plugs, fuel pump.

I did notice that my truck doesn’t seem to have the high idle that other TBIs have. I notice right from cold start that the rpm’s don’t stay higher and then gradually come down, it just starts and instantly goes down to 650rpm and runs rough until she warms up. Could a bad IAC or something cause this?

What else do you guys think it could be?

I do have a small exhaust leak from the header flange because my shorty headers have a crack. It is before the one O2 sensor, so could that be throwing off my AFR?


Considering getting a reddevilriver tool to hookup to TunerProRT for live data.

 

[JPVortex]

Also to be noted, when first starting for the first time of the day, sometimes the truck won’t start first try. It’ll crank over and pop off for a second then die. Usually this happens no more than twice before it starts but then doesn’t run right until warm.

I also do have a pretty open exhaust system with shorty headers into a cherry bomb glasspack.

 

[WICruiser-97]

Sounds like the temperature sensor for the ECM is bad so the engine thinks it is warm when its not. There are 2 temperature sensors one for the guage and one for the ECM. The one for the ECM is near the thermostat housing. They are not to expensive or hard to change.

 

[BVRPLZR]

Do you have a scan tool?
Easy way to check if you're jumping into closed loop/the CTS is incorrect right off the bat

The cracked headers before the O2 shouldn't be messing with your AFR because *normally* right after starting you'd still be running in open loop without input from the O2 sensor

 

[RichLo]

Good suggestions so far. Check injector spray pattern, if possible, have somebody else crank as you watch on a cold start. Check fuel pressure next.

You can also take the IAC off and clean it and the passages with deep creep spray foam. It wont completely fix the problem but it may improve it to give you a direction to go.

 

[JPVortex]

Sounds like the temperature sensor for the ECM is bad so the engine thinks it is warm when its not. There are 2 temperature sensors one for the guage and one for the ECM. The one for the ECM is near the thermostat housing. They are not to expensive or hard to change.

I may try replacing it again. I replaced it 6 months ago with an autozone one, but I wonder if it already is going bad.

 

[JPVortex]

Do you have a scan tool?
Easy way to check if you're jumping into closed loop/the CTS is incorrect right off the bat

The cracked headers before the O2 shouldn't be messing with your AFR because *normally* right after starting you'd still be running in open loop without input from the O2 sensor

I don’t, but I’m strongly considering buying a usb to ALDL from reddevilriver to check out that stuff.

 

[JPVortex]

Good suggestions so far. Check injector spray pattern, if possible, have somebody else crank as you watch on a cold start. Check fuel pressure next.

You can also take the IAC off and clean it and the passages with deep creep spray foam. It wont completely fix the problem but it may improve it to give you a direction to go.

Injector flow is great, forgot to mention about a month ago I completely rebuild the TBI unit, did not help the cold running at all.

The IAC is definitely something I will check out.

I tried checking the fuel pressure before rebuilding the TBI but the crappy harbor freight TBI adapter in the kit leaked everywhere.

 

[BVRPLZR]

I don’t, but I’m strongly considering buying a usb to ALDL from reddevilriver to check out that stuff.

I had a terrible experience with trying to get a USB to ALDL cable from reddevilriver on ebay.
Ordered it and payed immediately and got totally ghosted even after a couple weeks and several messages. This is just my experience but I would steer clear.

I have no experience with BoostedNW, but they seem to have taken over from Moates, who I had a great experience with (although literally the day after I bought my cable from Moates, they abruptly shuttered the business)

 

[JPVortex]

I had a terrible experience with trying to get a USB to ALDL cable from reddevilriver on ebay.
Ordered it and payed immediately and got totally ghosted even after a couple weeks and several messages. This is just my experience but I would steer clear.

I have no experience with BoostedNW, but they seem to have taken over from Moates, who I had a great experience with (although literally the day after I bought my cable from Moates, they abruptly shuttered the business)

Wow! Thank you for the heads up. Will definitely look elsewhere.