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Discussion Starter #1
I am new to the forum and appreciate the opportunity to read everyone elses troubles and ideas. I need your help! My 94 6.5 Suburban is stalling. No consistencies! I'm in California - so it's not cold. I have changed the fuel pump which has given me trouble over the last couple years. Fuel seems great now but not my problem. The truck stalls going down the freeway, sitting in the driveway, in parking lots, during fueling. It stalls after 200 miles, or only after 5. There seems to be no consistencies. I have changed the fuel filter, the fuel pump, the fuel pump relay. I don't want to go in to the dealer for a diagnostic - already over the phone they are trying to sell me a new injector pump - I don't think it is that since it is so inconsistent. I have been reading your forum and am leaning towards the ignition switch, oil pressure switch, electrical connections, or possibly the FSD since I have had recent trouble with the AC kicking off - don't know if there could be a relation???? Any help you guys could give would save me money!!! My trucks got 140K on it. Can't wait to hear your opinions and suggestions -


Okifide -
 

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Hello okifide


If you've read down thru the posts, you'll see this is a recurring theme, with varying symptoms and many suggestions for troubleshooting. Model year is unimportant - procedures are workable for all the EFI engines.


The magic answer is the one you accomplish the tasks for, and it solves the problem.


Try the labor-only tasks first - labor only, doesn't cost anything to inspect and clean. Your choice as to order of progression - perseverance is the key.


And, it's a good preventive maintenance routine for the older trucks.


Eliminate the good stuff, what's left is the bad.


Maybe you won't need an ign switch, or an FSD - some folks just buy and replace them anyway, to eliminate them first.


And, if you post your results here, it's help for the next new guy with stalling problems, right?


Good wrenching to you. Edited by: gmctd
 

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First off lets clear up the AC. If your truck is several years old it is most likely just low on ref. All ACs leak over time and GM has built in a low pressure switch that cuts off the compressor when the ref. is low. To check this, lift the hood, start the truck and rev it up to about 1000 rpms with the AC on and the doors open. If the compressor shuts down with a min or so remove the 2 wire connector on the receaver and jumper the connector with a paper clip and test again. If the AC remains on when it had shut down in the last test you are low on ref.


Now for the stalling. If you are not showning any codes after a stalling it is most likely the FSD. Once the truck cools and restarts it is highly unlikely an electrical connection or ign switch would cause this. The average dealer has no idea how to change a pump so I would not risk having them touch the truck.


Take a look at my site, noted in my signature, and see were mine is mounted under the bumper. That is a Heath unit.Edited by: HowieE
 

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Discussion Starter #4
I've located the FSD on my truck - Thanks for your advice. Can anyone let me know how to test the FSD - or do you just replace it? Can anyone give me directions on replacement? Does the intake manifold have to be removed? I'm not touching it until I hear from you guys.


Thanks again -


Okifide
 

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I removed the intake - some say it can be done without, but it's much easier for me.


Remove the PMD, finish up the intake R&R procedure with new gaskets and sealer. You probably will not want to re-mount the module to the inj pump.


Once you have the module off, pop the plastic covers off the transistors, and check the four 1/4-20 kep nuts - they left the factory tightened to about 5"-lbs torque.


Back them off, run down to finger-tight, then 1/4 turn more with a socket. This re-establishes electrical contact.


You can re-connect the plug, lay the module transistor-side up on the engine, and start the engine.


If everything seems ok, fasten it to a suitable heatsink, and bolt it to one of the bosses meant for the TURBO_POWER cover.


Try it for a week - if it no further symptoms, consider mounting it out of the elevated thermal blast from the fan with a harness extension.


You might also consider a spare FSD, just in case.


By the way, when it's in your hand it's the Fuel Solenoid Driver FSD.


When it's on the inj pump, it's the Pump Mounted Driver PMD.


Subtle difference.....
 

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I converted my intake to an "F" lower and a fabricated upper on my 95' Tahoe, while I had the intake off I relocated my functional FSD to the grill area. Removing the FSD with the intake on would have been impossible without destroying it. If you are going to replace it I would suggest leaving the bad one right where it is and installing the new one where ever you can get the best air flow over it. I hope this saves you some work.


Don't R&R the intake to relocate a bad FSD.
 

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I would either mount the FSD either back on the pump or remote but NOT ON INTAKE .....they will fry there.
I did like Howie mounted the Heath kit but I mounted it on top of the frame cross member about under the seat area. (under truck). My intake mount went 30,000 miles pump PMD 100,000+miles. Get it out of the heat! keep it
 

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Discussion Starter #8
Wanted to give an update. I found that the fuel solenoid mounted on the fuel injection pump was leaking. I replaced the internal O-Ring - stopped the leak. I relocated the FSD just outside the turbo cowling to run for awhile to see if my stalling problem continues. Also changed out the oil pressure switch since it was easy to get to. I'll let you guys know how it turns out. Thanks again for your adivce.


Okifide
 

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As long as you are in there that deep you should do the oil pressure switch mode to save that new switch. The fuel pump draws about 4 amps and the oil pressure switch is rated for 1 amp. There is a drawing on my site that shows you how to rewire the switch so you reduce the load on the switch contacts.
 

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Appreciate the update. What did you find with the FSD module, or did you opt for replacement, only?
 

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gmctd


Who are you addressing your question to?


"Appreciate the update. What did you find with the FSD module, or did you opt for replacement, only"
 

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Actually, Howie, it was for okifide, but I'm just as interested in results from your failure. Don't recall that you ever posted any particulars, just the corrective action.
 

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Discussion Starter #13
The date is 5/1 and wanted to give all of you an update. Your advice was a success for me. I moved the FSD to the top of the manifold with the original harness. I also replaced the oil pressure switch. I don't know which one was my problem but the truck hasn't died since.



Thanks again -


Okifide
 

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gmctd


I have posted several of my problems and solutions on my web site rather than repeat them in several posting on different sites. With the aid of pictures I hope this is a better presentation.


http://mysite.verizon.net/vze54tx9/


Edited by: HowieE
 

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Okifide,


That's a good start. Follow through with the OPS bypass to save the OPS and move the FSD further away from the engine. The intake is convienent for replacement, but the worst for heat. I cut and spliced my own extension to put another 42" distance in the wiring harness and it hasn't faltered once (even though I should have sodered the splices).





The red wireloom is my homemade FSD relocator. I mounted the FSD on the firewall, but anywhere away from the engine must be an improvement.
 
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