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Ron
Ron, ASE Certified Technician
Category: GMC
Satisfied Customers: 33407
Experience:  35 years in the Automotive repair business.
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My 90 gmc k1500 started spilling back while driving and

Customer Question

My 90 gmc k1500 started spilling back while driving and almost stopped running.I found alt.was over charging and replaced it along with battery as it had damaged it. The problem still excists although if I disconnect single lead from alt. It runs much better but does not solve problem.
Submitted: 10 months ago.
Category: GMC
Expert:  Ron replied 10 months ago.

Hello, my name is ***** ***** I am a professional here at Just Answer. I have noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

Can you please explain what you mean when you say its spilling back ? Also if you connect a volt meter to the battery with the engine running what is the voltage reading. If possible can you also scan the computer system and see if there are any fault codes setting. Post back with the results when you can and we can work from there.

Customer: replied 10 months ago.
Like timing is off spitting back thru intake and getting 15.8 v
Customer: replied 10 months ago.
Sorry 14.8 volts
Expert:  Ron replied 10 months ago.

Your charging voltage is fairly close as long as it not going any higher, the normal charge rate is usually not much higher then 14.2 volts so you are a bit on the high side. Spitting through the intake usually indicates a valve timing concern. Are you able to place a timing light on the engine while the problem is occurring and monitor the timing?

Customer: replied 10 months ago.
OK not home at moment but will b in a few hours also no codes in ecm.
Expert:  Ron replied 10 months ago.

Okay then let start with having a a look at the timing to see if its holding steady.

Customer: replied 10 months ago.
OK so ll be home about 10:30 am eastern time. I'm truck driving
Expert:  Ron replied 10 months ago.

No problem, Im here all day.

Customer: replied 10 months ago.
OK timing holding steady and has not changed since I set it about a year ago,also alternator shows 14.3 volts using a digital meter
Expert:  Ron replied 10 months ago.

So when do you hear the popping through the intake? Dose it happen under load?

Customer: replied 10 months ago.
My daughter drove truck to school shut off on her positive had got loose,was tightened back up. It ran fine for about 50 miles then it started doing this. I'll explain again as I did in my question. Truck will run fine for about a mile,then it starts sputtering and want take gas. This spitting back I hear I assume is thru the intake,it may be into the headers but does not backfire thru exhaust. When it starts acting up it want run over 30 mph and will eventually stop taking gas altogether. When I unhook alt truck will run to at least 60 only if you don't over apply the throttle so yes I guess you could say when its under a load only when alt is disconnected.
Expert:  Ron replied 10 months ago.

If the timing is holding steady the I would start next with monitoring the fuel pressure to make sure the fuel pump is holding proper pressure. Normal pressure on your 5.7 should be right at 10 14 PSI. Anything less then 10 PSI would indicate a failing fuel pump or restricted fuel filter.

Customer: replied 10 months ago.
OK I'll check fuel pressure and fsil to mention that I had already checked the filter.
Expert:  Ron replied 10 months ago.

Okay then install a fuel pressure gauge and monitor the fuel pressure while the problem is occurring.

Customer: replied 10 months ago.
OK here is what we have 22 lbs fuel pressure when just turning key on and 14 when running down the highway. OK after hooking up pressure gauge and driving down road truck ran like a champ, I was puzzled I got truck up to 70 no problems. Then I noticed alternator not charging,so I stopped hooked lead back up on alternator and drove truck 1/4 mile and it started same problem again. I payed better attention to symptoms and and have spit back thru intake and lite backfire thru exhaust.
Customer: replied 10 months ago.
Sorry 12 lbs fuel psi when just turning on key and 14 driving
Expert:  Ron replied 10 months ago.

Was it spitting once the alternator stopped charging. Did you address the no charge problem?

Customer: replied 10 months ago.
No spitting if alt not charging and yes new alt but had same problem with old alt.
Customer: replied 10 months ago.
Old alt was overcharging new one 14.3 volts on output. If I unhook brown wire to stop alt from charging truck runs fine. Reconnect brown wire on alt problem comes back
Expert:  Ron replied 10 months ago.

Are you sure that circuit is not shorting out. Somethings not making sense here.

Customer: replied 10 months ago.
I would assume it's not there is no sign it is no overcharging oo alt part no blown fuses how would you suggest I check for a short.
Expert:  Ron replied 10 months ago.

I would start with checking the brown wire. Which brown wire are you unhooking?

Customer: replied 10 months ago.
The one that connect to the alternator and I believe it go to the alt guage in the cluster according to wiring diagram I found online
Expert:  Ron replied 10 months ago.

Okay there has to be some issue with this wire or the circuits it controls if the truck runs okay with it disconnected. That the circuit you are going to need to check.

Customer: replied 10 months ago.
OK I will check it out and let you know what I find .
Expert:  Ron replied 10 months ago.

Okay, Im off this morning but will try and check in this afternoon. Good luck on the hunt.

Customer: replied 10 months ago.
Thanks
Customer: replied 10 months ago.
OK could not find a problem added and extra ground wire and seafoam into gas ran 3 miles before acting up. I did run a code check and came up with code 43. Electronic spark control low voltage and/ or electronic spark control circuit problems.could low voltage be from running without alt charging keepnin mind it was only a short distance and battery is fully charged.
Expert:  Ron replied 10 months ago.

The code 43 can be set due to any of the following,

  • Knock Sensor Connector
  • Knock Sensor Wiring
  • Knock Sensor(s)

    You can check it and the circuit with the steps in the link below. Copy and paste the link to your browser to open and view them.

    https://dl.dropboxusercontent.com/u/104923897/Knock%20sensor%20Jan%2031.pdf
Customer: replied 9 months ago.
OK so I fixed my truck not really sure the connecting between the alternator and firing system,bit by replacing the magnetic coil on the distributor it fixed my truck.
Customer: replied 9 months ago.
I found no problem with the spark knock sensor or circuit or alt circuit , I had eliminated every other component by testing and or trying a new part. The coil was my last component and by replacing it my truck ran as it should have.
Expert:  Ron replied 9 months ago.

Glad to hear you got it resolved. Good work. Thank you as well.

Customer: replied 9 months ago.
Thank you I appreciate your help.
Expert:  Ron replied 9 months ago.

Your very welcome and that you as well. Please take a moment to rate my service so I can get credit for my time, the question remains open for follow up even after doing so, all you need to do is return to this question if need be.

Thank you again.