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High Idle Stall 1990 Blazer TBI

Recon0321

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Guys,

I'm at a loss with this issue. I've read multiple forums here, and it sucks to see the original posters not come back to say what resolved their issues (if they were resolved). I will do my best to explain everything that I have done to isolate this issue. With that being said, the problem still persist. I have to sell this blazer, but I will not pass this problem on to another person.

I've read all over the place tested replaced everything under the hood. It only happens when the truck is in a closed loop and the truck has reached operating temp. The idle is all over the place. Sometimes I get a low idle as if it's going to stall at a stop. I can also get a somewhat normal idle at a stop. At times the idle and truck will surge while I'm at a stop. And at times I can hear the idle range from low to high. When I get a high idle at a stop, as soon as I apply gas, it sputters a little then dies. If the idle is high at a stop, and I don't touch the gas, the idle will remain high. It will only die when I touch the gas. I can usually turn right over, and drive, however, it will happen again. I've only noticed this in drive and while at a stop, if I keep moving it doesn't happen. In drive, the idle is rough and surges. I never have an issue accelerating, or a lack of power while moving, only when I come to a stop. I'm at a complete loss. What I've done so far:

Checked for vacuum leaks, replaced all vacuum lines, replaced o2, ESC, TPS, IAC, EGR valve and solenoid, replaced injectors, distributer, ICM, plugs/wires, ECM, fuel pump, sending unit, relay, fuel pressure regulator, TCS. All parts have been changed with original delco parts except for the dizzy and coil which is MSD. I hope someone can point me in the right direction, and I will post my findings to help the next poor soul who is chasing a unique issue. I'd like to thanks those in advance that help!

Here are the threads that I read that have issues similar to my issue.

https://ck5.com/forums/threads/1990-k5-350-stalls-in-gear-after-warmed-up.290792/
https://ck5.com/forums/threads/rough-idle-when-in-drive-and-stopped-only.338965/#post-4042805
https://ck5.com/forums/threads/1991-k5-tbi-issue.336706/page-2
https://ck5.com/forums/threads/hunting-for-idle.329800/
 

1-ton

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One thing you can do is take the air filter box off, and then start the engine. Look down the TBI while it is running to see if a normal spray pattern from the fuel injectors is happening.
 

Recon0321

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One thing you can do is take the air filter box off, and then start the engine. Look down the TBI while it is running to see if a normal spray pattern from the fuel injectors is happening.

1-ton, I've looked at the spray pattern on several occasions, and it seems to be in a cone shape pattern with no drips. Is there something specific I should be looking for? I swapped the injectors about a month ago with Delco injectors.

Thanks
 

1-ton

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1-ton, I've looked at the spray pattern on several occasions, and it seems to be in a cone shape pattern with no drips. Is there something specific I should be looking for? I swapped the injectors about a month ago with Delco injectors.

Thanks

I sounds like the injector spray pattern is good. Is your TBI an aftermarket Holley or Big Block TBI? Could check to make sure throttle linkage is not binding.

Another thing you could do is go to this link https://www.tunerpro.net/. Download TunerPro, install it onto a laptop (if you have one). Then you need to get a data cable (pictured below), and the proper definition files for your ECM here...http://www.tunerpro.net/downloadBinDefs.htm#GM, and then you can interface with your ECM to see what your engine is doing.

I am posting a short video of some data logging I did with TunerPro on my TBI engine. At about 4.25 minute mark in the video is a screen called "default view". This part of TunerPro will tell you which sensor is not working correctly.

8947.jpg


 
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Wes Harden

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So I take it there are no computer codes? have you tried wiggling the wiring looms while the engine is running ? if not I would try this with everything you changed the loom is the only thing left. Do you still have your old computer? also you didn't state if the t body base gasket was checked these were notorious for giving out, and cause a vacuum leak. remove pcv from valve cover and squirt small amounts of brake or carb clean in valve cover observe idle, if it improves your intake is leaking either at the gaskets(common if heads have been milled) or cracked intake.
Do you have a vacuum gauge? watching the needle when the engine is running poorly can help with diagnoses.
 

Recon0321

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I sounds like the injector spray pattern is good. Is your TBI an aftermarket Holley or Big Block TBI? Could check to make sure throttle linkage is not binding.

Another thing you could do is go to this link https://www.tunerpro.net/. Download TunerPro, install it onto a laptop (if you have one). Then you need to get a data cable (pictured below), and the proper definition files for your ECM here...http://www.tunerpro.net/downloadBinDefs.htm#GM, and then you can interface with your ECM to see what your engine is doing.

I am posting a short video of some data logging I did with TunerPro on my TBI engine. At about 4.25 minute mark in the video is a screen called "default view". This part of TunerPro will tell you which sensor is not working correctly.

8947.jpg



1-Ton, to the best of my knowledge I have the standard TBI. I installed tuner pro and purchased the usb adl cable about six months ago, trying to find what was causing the rough idle. I have the data streams from open/closed loop, with two 20 minute drives. At the time my voltages for the o2 sensor were off, so I replaced that, still no change. The stalling just started happening recently so I'm trying to figure out if I have two separate issues. One of the challenges I ran into using tuner pro was deciphering some of the data streams and making sure I had the correct bin for my setup, as there is a learning curve. I'll take a look at your video and give it another shot.

Thanks!
 

Recon0321

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So I take it there are no computer codes? have you tried wiggling the wiring looms while the engine is running ? if not I would try this with everything you changed the loom is the only thing left. Do you still have your old computer? also you didn't state if the t body base gasket was checked these were notorious for giving out, and cause a vacuum leak. remove pcv from valve cover and squirt small amounts of brake or carb clean in valve cover observe idle, if it improves your intake is leaking either at the gaskets(common if heads have been milled) or cracked intake.
Do you have a vacuum gauge? watching the needle when the engine is running poorly can help with diagnoses.

Wes, you are correct there are no codes. I was getting a 43 code and when I changed the ESC module that's the last i've seen of that code. When it stalled on me about two months ago I cracked the hood started it again, and did just what you recommended several times. I wiggled the wires/vacuum lines to see if I could recreate the problem, with no noticeable change. I was hoping it would be that easy! I still have my old computer with two test computers that I've swapped, the issue is still present with all three computers, so I've ruled that out. When I replaced the injectors about a month ago, I also replaced the TBI gasket and torqued it to spec. I have not tried spraying into the pcv port yet. The Edlebrock intake is only a couple of years old as it came with the new motor. I have not used a vacuum gauge yet, however, I will look into it.

Thanks!
 

1-ton

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1-Ton, to the best of my knowledge I have the standard TBI. I installed tuner pro and purchased the usb adl cable about six months ago, trying to find what was causing the rough idle. I have the data streams from open/closed loop, with two 20 minute drives. At the time my voltages for the o2 sensor were off, so I replaced that, still no change. The stalling just started happening recently so I'm trying to figure out if I have two separate issues. One of the challenges I ran into using tuner pro was deciphering some of the data streams and making sure I had the correct bin for my setup, as there is a learning curve. I'll take a look at your video and give it another shot.

Thanks!

You must have the correct definition files are TunerPro would not establish a connection with your lap top, in order to do the data logging you have done. I think there is a sensor input that is not functioning correctly, and the "default view" function in TunerPro will show what all the ECM sensors are doing plus a couple of other things like the charging system voltage, and fuel pump voltage. The "default view" function in TunerPro is not a data logging function. It is just a reader that shows in live time what the sensor values are like voltage and resistance.
 
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Wes Harden

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Re torque TBI and intake when you get a chance, was the motor new, or remanufactured? Remanufactured the heads were milled and this will change the angle and gap thickness at the intake to head seal. If the milling is severe the intake can hit the valley before it clamps the gasket to head.
The intake can be machined to correct for this.
 

1-ton

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Re torque TBI and intake when you get a chance, was the motor new, or remanufactured? Remanufactured the heads were milled and this will change the angle and gap thickness at the intake to head seal. If the milling is severe the intake can hit the valley before it clamps the gasket to head.
The intake can be machined to correct for this.

I am going to re-torque my TBI this weekend. Even though my TBI engine is running just fine, it has been about 7 or 8 months since the last time I re-torqued it. Those things come a little loose every few months or so. I double gasketed my TBI base plate, in order to make sure it sealed properly from vacuum leaks.
 

Chevy305

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Have you looked at your IAC valve? I don't think that was mentioned. Over time dirt or carbon can build up and make it sticky or not seat fully.
 

formercruiserhead

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You said you replaced the egr valve, but are the ports in the intake clear? Just did my intake gasket today and ports totally blocked.
 
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