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Roy
Roy, import/domestic specialest
Category: Car
Satisfied Customers: 1773
Experience:  ASE master tech for 40 years
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1998 GMC Yukon wont start !! Here is the breakdown.. 3 fuel

Customer Question

1998 GMC Yukon won't start !! Here is the breakdown.. 3 fuel pumps in the last couple months..Truck ran fine for a week or so after each new pump then would not start.. Replaced Throttle position sensor, fuel regulator (twice),fuel filter, gas cap, fuel relay switch.. I have read all kinds of things on these forums and have not found anything that works... No codes coming up on diagnostics..No engine light .. What I have found that works is I can prime the intake with fuel and put the air cover back on and the truck will start and stay running and run fine at all rpm. If I shut it off ,it will not start again...Prime the intake and it starts and runs fine...???
Any Help will be great, cause I am stuck and have already dumped a pile of cash into this rig... Thanks Keith
Submitted: 1 year ago.
Category: Car
Expert:  Roy replied 1 year ago.
good afternoon my name is Roy and I will assist you today.

One issue on these was the connector at the fuel pump. bad connections and high resistance on the ground side lowers the voltage to the pump causing all kinds of problems.

the brand of fuel pump is critical as well. we have multiple problems with aftermarket pumps and found GM pumps worked the best.

the fact that you have to prime it tells me that the initial fuel pressure is too low for it to fire up but high enough for it to continue to run.

I would start with a fuel pressure test. you can rent one from a parts store to verify the actual pressure running and when starting.

the last thing is the tank. if your tank has debris in the tank, that alone will kill a new pump as sucking up this debris will lock up a fuel pump whether it is new or not.

Roy
Customer: replied 1 year ago.

All 3 pumps were ac delco pumps and new wiring harness were also put on at the time of installation by certified technicians..The tank debris I have no idea, due to the fact that I never replaced the pumps myself...If a pump does not have enough pressure to start then how can it maintain high rpm for a prolonged period when running?

Expert:  Roy replied 1 year ago.
ok, all new information I did not have. at 55 lbs or so, if you have less than that by like 10 lbs, it will be difficult to start or not start at all. once running it can run on lower pressure with performance. it will eventually set lean codes for not enough fuel.

what did the shops suggest to you about the issue???

Debris and fuel quality are always a possibility in multiple pump failures

Roy
Customer: replied 1 year ago.

The shops just replaced the pumps and faulted the regulator for the problem with them burning out...but the last new pump was done with a new regulator and it only lasted a few weeks and the same ole situation... I talked to the technician and told him i was able to start the truck once primed so all he could say was possible leak in fuel lines causing a vapor lock or something. I inspected the lines for any fuel leaks and did not see anything, even with the pump pressured and the truck running. One note that my wife had noticed is when we picked up the truck from the last shop we went to start it and there was a little hesitation starting and then it fired right up.. She said that it did that with all the replacement pumps as well..She asked if they even fixed the problem, because it had never acted this way until the first time it died on her...Which was the 1st pump that was replaced a few months ago....

Expert:  Roy replied 1 year ago.
leak in the lines would show fuel on the ground or if it is leaking back to the tank, then it would only be an extended crank time. no vapor lock anymore. if there is enough pressure to run the motor, that is plenty to overcome vapor lock.

there is another issue here but we need to start with a basic pressure test.

Roy
Customer: replied 12 months ago.

Hi Roy, I did a pressure test and ignition on fuel primes to 40lbs, but obviously will not start. I prime the intake manually and start the truck and pressure reads 54lbs while running at any rpm. Turn off ignition and fuel pressure jumps to 56lbs and then drops to 40lbs. The fuel pressure drops then from 40lbs to 30lbs in about 6 minutes.


 

Expert:  Roy replied 12 months ago.
ok, when you first turn the key on, does the pressure go to 58-60 lbs??

Roy
Customer: replied 12 months ago.

No it only goes to 40.

Expert:  Roy replied 12 months ago.

ok, the pressure issue is the pump itself. is this one of the gm pumps??

 

Roy

Customer: replied 12 months ago.

All three pumps were AC Delco pumps

Expert:  Roy replied 12 months ago.
I remember you saying that, very odd.

did you check the actual voltage to the pump to be sure it was 12 volts??? Make sure the ground is good as well.

Roy
Expert:  Roy replied 12 months ago.
how are you making out??

Roy
Customer: replied 11 months ago.

Hi Roy, I have removed the tank now and am going through everything and making sure to test voltage and checking all of my lines..I have a new pump but I don't want to put it in until I know everything is good. I tried to check voltage while it was in and it would just flash 10 to 12.3 volts while priming and would not hold a steady reading. I am going to try today to get an accurate reading with the tank out of my way.

Expert:  Roy replied 11 months ago.

ok, look for 12 volts or battery voltage.

 

make sure the ground is good otherwise you can have 12 volts and with a bad ground could drop the voltage low.

 

roy

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