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94 suburban issues

3K views 28 replies 11 participants last post by  FloridaHorseman 
#1 ·
lately it has been acting strange. its not everyday but more often lately the truck will sputter. doesnt matter if going down the highway or just idleing. almost like it hiccups. i just had a heath pmd isolator installed in march. and once in a while the gauge cluster will show like the key is turned forward but but not actually running when it actually is. battery light is on and rpm's aren't even registering. from what i am reading it could be anything from a bad ground to the ip to the optic sensor in the ip. the local shop i take it to said most likely its the ip but could be the optic sensor and should put some sea foam in to possibly clean out the sensor. does this make any sense to you guys? and if it is a bad ground then where would that most likely be at? getting frustrated. thanks in advance for any feedback
 
#2 ·
Sounds like you have significant battery connection issues and or a bad alternator. I would start with the connections at the batteries. For the dual stacked ones take them apart and make sure they are clean. Bad connections can stress out and kill the alternator. With the dual batteries you can get all sorts of odd things going on that normally would not happen.
 
#3 · (Edited)
Tach gets its signal from the alternator. Combined with your BATT light being on I'd say the place to start is checking all 4 battery connections and their grounds. Then stop by the auto parts store and get a free ALT check to see if it's putting out any voltage. You may also want to start carrying some jumper cables until you get it sorted out. ~FH
 
#4 ·
As they referenced, clean and make sure all the grounds are tight.
 
#5 ·
it has two new batteries. all connections are clean and alternator tested good. going to put sea foam in it tomorrow and cross my fingers. i was thinking if it was a ip issue then it would be consistent, but its not. i took it to get looked at yesterday and it wouldnt act up.
 
#6 ·
where does your guys voltmeter read? mine is about two notches under 14. originally i had thought it was the alternator but it tested alright. might just replace it and see if it makes a difference. do they make a heavy duty one?
 
#7 ·
Check the voltage across your batteries with a voltmeter. Should be at least 13.5 with engine running
 
#8 ·
so all battery connections been taken apart, cleaned. both grounds mounting to the top of the block look good. cleaned ground on passenger side of engine bay. is there any that I am missing? has been fine all week until today.
 
#9 ·
this weekend put in a new alternator. serpentine belt and still sputters. checked vacuum pump,fuel filter, and lift pump. all are fine. like i said before the pmd has already been replaced so more than likely its the injection pump. my question is where or who has the better pumps? have a friend that works at a dealer that can get me a decent deal or is there somewhere that has more reliable pumps? or are they all pretty much the same? from what i've seen they all come with only a one year warranty.
 
#10 ·
Have you done the lift pump test? Perhaps you have a bad OPS?
 
#11 ·
checked the lift pump already. talked to 3 different diesel mechanics that i know and they all are pretty sure its the IP.
 
#12 ·
Maybe a bad ignition switch?
 
#13 · (Edited)
... i just had a heath pmd isolator installed in march. and once in a while the gauge cluster will show like the key is turned forward but but not actually running when it actually is. battery light is on and rpm's aren't even registering...
I can't quite figure out what you mean by "the gauge cluster will show like the the key is turned forward but not actually running when it actually is". Key ON and the gauges go to a test position first and then go to actual engine signals after start. Are you saying the gauges go full travel while the engine is running and then return to normal engine readings?

The erratic gauge and battery light behavior shouldn't be caused by a faulty IP... but inversely, a bad ignition/key cylinder could cause the IP to cut in and out. Have you seen any correlation between the odd gauge activity/battery light and the sputtering condition or are they independent of each other?

If the IP problem started after you installed the PMD relocation kit you should probably check the extension harness. And make sure the ground wire is still attached to the torx screw on top of the IP cover plate and not attached to the new heat sink. It wouldn't hurt to Tee a fuel pressure gauge into the input line at the IP with an extension long enough to reach your windshield cowl and note the fuel pressure when the sputtering occurs. That should isolate fuel supply (LP or clogged fuel tank sock) problems from IP/PMD electrical problems.

Without more information and test results I don't know how your "mechanics" all agreed it's a bad IP. It sounds to me like either the ignition circuit is shorting somewhere (bad key cylinder?) causing the IP to cut out or you have two unrelated problems, electrical and fuel supply, each skewing the diagnosis. A fuel pressure gauge should narrow it down some. ~FH
 
#17 ·
its weird, you'd have to see it. when the truck is running sometimes it seems its in the test position. but only the battery light is on and the rpm's don't register until you start moving, but once you stop the needle falls back down again like its not running. its not all the time and there is no correlation between that and when it sputters. i changed the alternator because from what i understand is that the rpm's are controlled by the alt. haven't seen any problems since saturday when i changed the alt. i guess we'll see. checked the extension harness and did not see any problems with it. it is grounded to the torque screw on the top of the IP. as far as the ignition we have not checked that yet.
 
#14 · (Edited)
I have had to replace the ignition switches in all but one of our vehicles.

I had various undiagnosed problems that were cured with a new GM/AC Delco switch. Do not use an aftermarket.

How many miles are on the Burb?

It sounds as if you are having an electrical problem as apposed to a fuel problem.

If you are having an intermintent fuel problem it is good to check the tank sock. Stuff cvan plug the sock and then slosh around away from it only to be sucked back against it again later.

Did you hot wire the lift pump and run about 3/4 gallon out the drain while noting thhe flow?

I use a glas gallon pickle jar, let it sit 20 minutes and look for crud and water bubbles on the bottom.

When you change the fuel filter, do you suck out/clean out the bowl? I use a 12 volt in line fuel pump. A lift pump will work. If I suck out the excess fuel and there is still crud at the bottom of the bowl I use Sea Foam to clean it up and suck it out with the fuel pump again
 
#15 ·
Just as a maintenance item, I dropped the tank on mine a few weeks ago to check the sock. Not sure if I'm the exception, but my sock had a bypass valve in the end of it that opens if the sock clogs so that fuel will still flow.
 
#16 ·
That sock bypass was something I knew GM did in the early passenger diesels. I seem to recall its described in the service manuals. It said it was for cold weather operation. Apparently they felt that the fuel could be gelled enough to not go through the sock so they made that bypass. I was sort of thinking that if it was that gelled that just the soc would not be your only problem.
 
#20 · (Edited)
it is giving two codes. one is for the glow plug relay and the other one is 36. one of the mechanics said it was the ip. would a bad pmd make it give any codes?
 
#22 ·
MY truck was giving a 35 and 36 until I replaced the PMD. Hasn't thrown a code since then. Not sure if the new PMD is masking a problem with the IP or if the codes were being caused by the faulty PMD.
 
#21 ·
If it has GP relay code, I would work on the GP and the relay first.

Your problem sounds like an electrical issue. Check the grounds, once again.
 
#24 ·
Do you have a bunch of keys on your key chain ? If you do, take just the truck key off and drive with that for a while. If it seems to cure your problem, you have a worn out key cylinder, happens all the time to people with 49 keys on one chain. If not, ask the PO how many keys he has.
 
#26 ·
only have the two keys and a chain. nothing heavy. the previous owner might have had more.
 
#28 ·
just a update. it's been 3 weeks since it has acted up after I put in a new alternator. I've driven 1300 miles and I am currently in Colorado with it. at this point my guess was a combination of alternator and maybe bad fuel. not sure but is currently running fine. thanks for all the idea's and help.
 
#29 ·
Thanks for posting the apparent solution. ~FH
 
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