1994 Z-71 Cold start Runs bad 30 seconds??

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Durfman77

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This truck has been fine for me and runs perfect all day long----But when first started when cold it starts right up fine,,idles fine for about 20 seconds then starts acting like its being flooded with gas for another 20 to 30 seconds then clears right up and runs fine all day???
Just cant put my finger on whats going on?

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Catbox

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My 1995 Suburban will occasionally give me fits when it first starts up.
It will idle like it has a huge cam in it for 45 seconds to 90 seconds and then it evens right out.
I have put Seafoam in the tank and it helps clean that issue up.

But I haven't bothered to actually figure out what is causing it.
 

Frankenchevy

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I’d start by checking the fuel pump and filter.

Maybe a problem with CTS enrichment or after start enrichment. Not sure how those two items are controlled by the factory ecu.
 

bucket

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I’d start by checking the fuel pump and filter.

Maybe a problem with CTS enrichment or after start enrichment. Not sure how those two items are controlled by the factory ecu.

A faulty CTS can 100% cause a cold start issue like described.
 

AuroraGirl

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i mean, not a square body. but definitely digging the truck, looks real nice. Any check engine lights?
 

Durfman77

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No engine codes at all am going to try the CTS change today and see?
 

scwaters

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Alright, what is a CTS? My K10 behaves the same way
 

Durfman77

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Well I tried the CTS today and No change?? So am getting an oxy. sensor next day or so and see if thats it???
 

SirRobyn0

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Alright, what is a CTS? My K10 behaves the same way
CTS = Coolant Temperature Sensor. @Durfman77 someone else said fuel pump possible issue and they are right. O2 sensors are not in play until closed loop so that won't effect the cold run at all. I would hook a fuel pressure gauge up to it and see if the pressure drops off when it acts up. Hooking up a scanner and monitoring the sensors when it is happening would sure be helpful. You might find an issue that way.
 

Bextreme04

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Just throwing parts at it will get expensive. Try and hook up to see what the various sensors are showing the ECU. If you don't know how to do that, at least test the sensors before trying to change them out.
 

Durfman77

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Thanks--I had a good CTS so just tried it,, I dont see how fuel pump would be problem when all day it runs fine and I pull a trailer with about 3600 on it about 3 times a week and runs good? NOT trying to argue or doubt you but just not understanding the fuel pump issue?

Just started this couple months ago I bought the truck 1 1/2 years ago and it never did this? 95 year old lady had it bought it new and had all service records.

I know about parts ,,just throwing parts at it goes against everything I ever did --just getting lazy I guess and looking for easy fix??

I put ele, fan on it last winter did all wiring myself dont think that could have any affect on this????
I can check pressure on it next couple days,,
 

Durfman77

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OH--I also put new exhaust on it last fall and knocked the cat out of it but dont think this started then if I remember right?
 

SirRobyn0

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Thanks--I had a good CTS so just tried it,, I dont see how fuel pump would be problem when all day it runs fine and I pull a trailer with about 3600 on it about 3 times a week and runs good? NOT trying to argue or doubt you but just not understanding the fuel pump issue?

Just started this couple months ago I bought the truck 1 1/2 years ago and it never did this? 95 year old lady had it bought it new and had all service records.

I know about parts ,,just throwing parts at it goes against everything I ever did --just getting lazy I guess and looking for easy fix??

I put ele, fan on it last winter did all wiring myself dont think that could have any affect on this????
I can check pressure on it next couple days,,
So the fuel pump issue would be this. It bleeds down over night and the fuel is replaced with air in the lines, you turn the key on and it pressures up, there is still fuel in the fuel rail, but there is now air in the lines, so it starts on the fuel in the fuel rail and then when it gets to the air it runs bad and once that is clear it is good all day. This is a problem I've seen on that generation chev truck before, testing the fuel pressure should help you identify that. BUT there's other sensors, that if monitored on a scan tool you might find one out of whack. Bottomline is tests need to be run, or you may end up spending a lot of time on money on unneeded repairs.
 

Durfman77

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Thank you!!! Now that makes sense to me for sure. Will be checking into that.
 

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