Author Topic: 90 Suburban runs rough and dies shortly after filling up.  (Read 11268 times)

Offline 90_suburban

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90 Suburban runs rough and dies shortly after filling up.
« on: October 05, 2018, 01:01:41 PM »
Ok I have a 90 r1500 5.7 tbi 190,000 miles. I stopped and got gas roughly 18 gallons to top off the 40 gallon tank. Drove it about 20 miles home and it died pulling into my driveway started right back up and pulled it into the garage with it dying once again, started right back up and finished parking. Couple of hours later went to go pick my kids up from school and it started up no problem and when leaving it sputtered and died. Started right back up and got going down the road it kept hesitating and sputtered some more and died again. This time it wouldn’t start back up without feathering the gas managed to get back home with it and take another vehicle to pick the kids up. My thought was bad gas.

Next day I replaced the fuel filter and dumped some fuel treatment in the tank. Now sometimes I can get it to start other times it won’t start at all. If I managed to get it started and try driving it, it will sputter some but sometimes run fine. I have managed to siphon around 8 gallons out and burned some out driving as well and topped off with premium gas close to 12 gallons. Now my thought is that it is something else and it just happened shortly after filling up and the gas is fine.

I picked up a ADAL scanner from oriellys too dang expensive but bought it anyways. My cel isn’t on but I pulled codes 32,34,42 from it. Being I have another suburban an 88 v2500 I changed the map sensor with no luck and I also swapped the whole tbi unit. This should rule out the map, iac motor, tps, the injectors, and fuel pressure regulator. Still no difference so I swapped the ignition control module one of the connectors on the 90 was broken so I thought it could be bad. Right now it is still the same. I have only owned it about a month and put around 1000 miles on it. Within the last year the PO replaced the fuel pump as well.


Anyone have any thoughts on where to start. I do have a new coil that will be here tomorrow I am going to try out.

Offline Captkaos

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #1 on: October 05, 2018, 06:54:26 PM »
Pull the distributor cap out and check if ti looks good, pull the whole distributor out.

I had one dying whe going in gear and this was the post on it.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=3984.0

BTW a wire between the AB terminal on the ALDL will flash the codes.

Offline 90_suburban

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90 Suburban runs rough and dies shortly after filling up.
« Reply #2 on: October 05, 2018, 07:11:59 PM »
I pulled the cap today when replacing the ignition control module both cap and rotor look relatively new inside. I bought the actual scanner so I can look at the little bit of live data it will show as well. According to it the map seems to be putting out good voltage it does show it to be running lean though when idling it will switch to rich for a second when revving up.

I will take a look at that thread and see what I can tell.


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Offline Irish_Alley

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #3 on: October 05, 2018, 09:56:45 PM »
can you swap computers?
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Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #4 on: October 05, 2018, 11:17:33 PM »
can you swap computers?


Yeah I could pull the one out and swap it in the other and give it a try. I guess the promm is the same in both of them?


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Offline Irish_Alley

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #5 on: October 06, 2018, 07:07:48 AM »
can you swap computers?


Yeah I could pull the one out and swap it in the other and give it a try. I guess the promm is the same in both of them?


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cant say 100%, the only issue i can think of is the trans and thats because im not sure how the 700r4 works in relation with the ECU if at all. does it seam to run different depending on if the engine is hot or cold?
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Offline VileZambonie

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #6 on: October 06, 2018, 07:50:36 AM »
Holy parts cannon Batman.

Check your fuel pressure, check for spark, check for injector pulse. Don't keep swapping parts around as you may begin to compound issues before identifying your initial issue.
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Offline 90_suburban

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90 Suburban runs rough and dies shortly after filling up.
« Reply #7 on: October 06, 2018, 09:04:58 AM »
Holy parts cannon Batman.

Check your fuel pressure, check for spark, check for injector pulse. Don't keep swapping parts around as you may begin to compound issues before identifying your initial issue.


I definitely have spark and fuel. With it cold this morning I was able to get it to run but wouldn’t hold a steady rpm. Once warmed up I couldn’t get it to start but for 1-2 seconds. I unplugged the idle air control motor and it fired right up and is idling at a high rpm but steady. I’ll test the iac motor and see if it is bad.

Not sure if it has anything to do with it or not but the brake light in the dash came on as well and hasn’t went back off. My thought is from braking with the engine off several times has caused it not sure what sets it.


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« Last Edit: October 06, 2018, 09:06:34 AM by 90_suburban »

Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #8 on: October 06, 2018, 09:19:49 AM »
After plugging the iac back up while it was running. It seems to be running perfect for now.



Screenshot of the live data at the moment. Seems to idle a little higher than before but could be the difference in the tbi units from the 88 to 90.

I turned it off and it started back up running normal still. Guess I’ll see how it goes.


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Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #9 on: October 06, 2018, 09:21:37 AM »
Didn’t last long back to how it was I’ll get to testing the iac hopefully that’s all it is.


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Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #10 on: October 06, 2018, 11:25:31 AM »
Seems like the iac is working. Right now it idles around 1000 which is high but it does idle. When I put it in gear it drops to 750 and you can hear the iac open up and I can watch the counts change on the scanner as well until the Rpms get to 850.

When I put back in park or neutral it idles as 1400 way high and the counts on the iac don’t change immediately. It take about a minute then it will slowly decrease back to 1000 rpms idling. It starts and runs fine with a little stumble coming to a stop.

Besides the computer what controls the iac motor? If it is only the computer then my assumption would be that it took a dump?


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Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #11 on: October 06, 2018, 11:38:50 AM »
Idle just after startup



In gear



Just after shifting back into park




After shifting into park and the rpms coming back down.




Iac counts start close to 100 just after start up climb to 140 in gear then back to idle the drop and steady out around 55.


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Offline VileZambonie

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #12 on: October 06, 2018, 10:14:24 PM »
Okay so don't blame the victim. If it's lean, idle is high and IAC is way off the mark, what's it doing? Compensating for a vacuum leak most likely or an extremely lean condition. Remember, garbage in garbage out. Are you chasing the symptom or the problem? So what's the issue now, just high idle? No drivability?
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Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #13 on: October 06, 2018, 10:35:46 PM »
Okay so don't blame the victim. If it's lean, idle is high and IAC is way off the mark, what's it doing? Compensating for a vacuum leak most likely or an extremely lean condition. Remember, garbage in garbage out. Are you chasing the symptom or the problem? So what's the issue now, just high idle? No drivability?


Most likely I’m chasing the symptom instead of the problem.

Mainly the issue now is high idle and the counts are high on the iac which is completely open. The O2 reading shows lean but if you watch the live data about every 2 seconds it bounces between lean and rich so my thought is that’s working correctly.

Correct me if I’m wrong but if it is a vacuum leak wouldn’t it go closed reducing the air needed?

I have sprayed carb cleaner all over and can’t find a vacuum leak (not that I notice anyways). Now even though the idle is high it will still occasionally not want to start or it will stall out it will also occasionally surge and not have a steady idle. It does still show to have a code 32 map sensor low voltage as well.

I guess it possibly could still be bad gas and I am chasing the symptoms as you say and the problem is actually elsewhere.


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Offline VileZambonie

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #14 on: October 06, 2018, 10:43:08 PM »
What's the TPS voltage?
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