Author Topic: 90 Suburban runs rough and dies shortly after filling up.  (Read 11269 times)

Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #15 on: October 06, 2018, 11:08:52 PM »
Tps voltage is .61 little higher than the .55 you recommended in the other thread. I was just reading more on that thread.


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Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #16 on: October 07, 2018, 10:06:13 AM »
I have a thought but don’t know for sure. My thought is that the iac counts are off because the computer is telling it to step and it only moves some of the time.

I was messing with it a little bit ago and after taking it around the block the counts stay full open at 145 (highest I have seen it go). When coming to a stop they come down and then go back up the 145 sometimes dying and sometimes it doesn’t. Idle in gear is 145 counts on the iac and 850 rpms I also watched it stay steady at 850 rpms and the counts go from 95 up to 145. On the way back from around the block it died and wouldn’t start back up until I unplugged the iac it started and then I plugged it back in. Made it home and when I put it in park the rpms climbed to around 1400 and the iac counts went from 145 down to 10 and idles at 1000-1050 rpms.


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Offline Captkaos

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #17 on: October 07, 2018, 12:16:29 PM »
Is the ECM throwing codes?  If so what are they?

You might try this ( I just skimmed these posts) it will reset the IAC.
Disconnect the battery for about 30 seconds and reconnect.
Jumper the A&B terminals on the ALDL connector
Turn the key on and leave it on for about 30 seconds.
Turn it off and remove the jumper.
Then try to crank.

Offline 90_suburban

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90 Suburban runs rough and dies shortly after filling up.
« Reply #18 on: October 07, 2018, 12:51:16 PM »
Is the ECM throwing codes?  If so what are they?

You might try this ( I just skimmed these posts) it will reset the IAC.
Disconnect the battery for about 30 seconds and reconnect.
Jumper the A&B terminals on the ALDL connector
Turn the key on and leave it on for about 30 seconds.
Turn it off and remove the jumper.
Then try to crank.


Only code it is throwing is code 32 low map sensor voltage. I’ve tried 2 different map sensors and both do the same thing.

I have tried the reset on the iac multiple times with no luck. With it fully extending blocking all air flow it will start but only stay running if I am giving it throttle.

I have read through the post on your truck. I have tried almost everything that you did as well. I don’t have a fuel pressure gauge adapter so I have one that will be here tomorrow and I will see what the fuel pressure is actually doing.


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« Last Edit: October 07, 2018, 12:53:12 PM by 90_suburban »

Online VileZambonie

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #19 on: October 07, 2018, 12:57:47 PM »
Tee in at the fuel filter. If all checks out as you say then I would suspect low fuel pressure.
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Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #20 on: October 07, 2018, 01:02:10 PM »
Will get that checked tomorrow when my adapter comes in. Hopefully that is it.


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Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #21 on: October 08, 2018, 12:51:03 PM »
Ok got my fuel pressure adapter in. Steady 12 psi in gear out of gear stays steady. Also got an iac circuit tester and it shows the circuit to be moving both directions.

I was mistaken on the code still showing. It’s a 34 not 32.


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Offline zieg85

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #22 on: October 08, 2018, 12:56:56 PM »
This may be a stupid question as I know very little about TBI engines.  Do TBI engines use a EGR valve?
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Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #23 on: October 08, 2018, 01:05:22 PM »
This may be a stupid question as I know very little about TBI engines.  Do TBI engines use a EGR valve?

Yes they do use one. I haven’t made sure it’s not stuck open yet fixing to check that. I have pulled the vacuum hose off of it and it makes no difference and also pulled the oil cap off with no difference. The oil cap was something I saw in another thread.


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Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #24 on: October 08, 2018, 01:29:04 PM »
Looks like the egr checks out. With it running I pulled open the egr manually and it idled down and tried to die. Closed it back and it idles again. Still idles at 1000 in P/N 850 in R/DL going back into park 1400 until the iac counts come down.

Every time I try taking it around the block even if it seems to run fine in the driveway. It will die coming to a stop and it won’t always start back up unless I unplug the iac and plug it back in.


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Offline 90_suburban

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90 Suburban runs rough and dies shortly after filling up.
« Reply #25 on: October 08, 2018, 02:58:52 PM »
Went back out and messed with it some more. I did notice that it seems to idle at a normal rpm when in open loop (didn’t have the scanner turned on yet so don’t know the actual value). As I was turning on the scanner and opening up the live data it went into closed loop and the idle jumped up.

Does this mean the O2 sensor is telling it to add more air?

Could the O2 sensor be bad and causing the issues with idling?


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« Last Edit: October 08, 2018, 03:18:04 PM by 90_suburban »

Offline MIKE S

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #26 on: October 08, 2018, 05:01:04 PM »
Make sure the vacuum supply line to map sensor is not plugged up with carbon. If it is, map sensor will respond to slow and have skewed readings.

Offline 90_suburban

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #27 on: October 08, 2018, 05:11:17 PM »
Make sure the vacuum supply line to map sensor is not plugged up with carbon. If it is, map sensor will respond to slow and have skewed readings.


Checked and it’s free. With it disconnected the map voltage goes high and throws code 33.


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Offline Irish_Alley

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #28 on: October 08, 2018, 06:43:33 PM »
is it smoking at all? i saw its reading lean but wondering if the computer is trying to compensate and giving too much fuel. not 100% sure how these tbis work and im still learning
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Offline Irish_Alley

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Re: 90 Suburban runs rough and dies shortly after filling up.
« Reply #29 on: October 08, 2018, 06:51:50 PM »
Code 34 - MAP Sensor
High Vacuum

Low or no output from
sensor with engine
running




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When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes