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5.7 hesitates

zthatzmanz28

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zthatzmanz28 Enthusiast

zthatzmanz28

Posted
Posted

Greetings Everyone,

 

Since I will have to wait for front leaf springs (according to my wife), I have anothet problem with the 5.7 gas engine.

 

When I start the truck and put it in gear the idle drops and the engine stalls.

 

It has been to the dealer and has had the following done:

 

Complete tune-up (new wires, plugs and distributaor cap) and fuel injectors removed and cleaned

 

Oxygen sensor replaced

 

MAP unit replaced

 

Every other sensor under the hood replaced

 

When the dealer hooked it up it showed a lean fuel mix then immediately said the mix was too rich.

 

I noticed it was particularly bad the other day when I went out while it was raining.

 

I suspected a faulty fuel pump and or in tank filter (external fuel filter has been replaced)

 

The dealer did not think that was the cause and suggested it was a vacuum leak or faulty canister in the vacuum system. :banghead: ?

 

 

Now I am wondering if it might be the on-board computer system that is causing the hesitation...It will sometimes hesitate when I take off from a stop or when I quickly accelerate.... :cheers:

 

Any ideas???

 

After replacing all the above the MPGs increased dramatically!!

 

 

THANKS!!!

 

Tim in Redford MI

  • 1 month later...
l87029 New Member

l87029

Posted
Posted
Greetings Everyone,

 

Since I will have to wait for front leaf springs (according to my wife), I have anothet problem with the 5.7 gas engine.

 

When I start the truck and put it in gear the idle drops and the engine stalls.

 

It has been to the dealer and has had the following done:

 

Complete tune-up (new wires, plugs and distributaor cap) and fuel injectors removed and cleaned

 

Oxygen sensor replaced

 

MAP unit replaced

 

Every other sensor under the hood replaced

 

When the dealer hooked it up it showed a lean fuel mix then immediately said the mix was too rich.

 

I noticed it was particularly bad the other day when I went out while it was raining.

 

I suspected a faulty fuel pump and or in tank filter (external fuel filter has been replaced)

 

The dealer did not think that was the cause and suggested it was a vacuum leak or faulty canister in the vacuum system.  :cheers:  ?

 

 

Now I am wondering if it might be the on-board computer system that is causing the hesitation...It will sometimes hesitate when I take off from a stop or when I quickly accelerate.... :gmc:

 

Any ideas???

 

After replacing all the above the MPGs increased dramatically!!

 

 

THANKS!!!

 

Tim in Redford MI

 

 

 

95Sierra2500 Senior Enthusiast

95Sierra2500

Posted
Posted

Def. sounds like a computer problem, but I don't know if these computers can be relearned or not...Another thing to check might be your cat. If it's original or just plain old it could be clogged.

zthatzmanz28 Enthusiast

zthatzmanz28

Posted
  • Author
Posted
Def. sounds like a computer problem, but I don't know if these computers can be relearned or not...Another thing to check might be your cat. If it's original or just plain old it could be clogged.

 

 

 

 

I changed the o2 sensor today. It now idles, but it fluxuates between 500 and 1000 RPM. I am believing it just might be that darn cat. It is hesitating from a dead stop and during acceleration when I am below 40-45 MPH. :gmc:

Koinz Enthusiast

Koinz

Posted
Posted

How about the TPS (Throttle position Sensor). Don't know if they are adjustable or not, but if it has a bad spot on the reostat, it could cause the problem.

zthatzmanz28 Enthusiast

zthatzmanz28

Posted
  • Author
Posted
How about the TPS (Throttle position Sensor). Don't know if they are adjustable or not, but if it has a bad spot on the reostat, it could cause the problem.

 

 

 

 

 

It was supposed to have been replaced just like the 0s was supposed to have been...It was my brother's truck and he had it in the dealership several times..

 

The throttle body was replaced and All the sensors we too?

 

I just did a quick check of the timing and it isn't even close to the mark... :cheers:

  • 1 month later...
  • 1 month later...
bluechevysled New Member

bluechevysled

Posted
Posted
i have a 1991 with the 350 that is doing the same thing. It doesnt run worth a s**t at any rpms higher than idle. have you found anything out?

 

 

 

 

i have a 1989 w/350 throttle body ive been told the gasket underneath will tend to leak one way to check is spray carb cleaner or something flammable at base if it idles up or runs smoother then you have a leak and need to replace

95Sierra2500 Senior Enthusiast

95Sierra2500

Posted
Posted

It worries me that you tell us that the timing isn't even close to where it should be (IIRC around 0*)...perhaps either your timing chain is stretched (how many miles are on the truck?) or it could possibly be a problem with your distributor.

  • 2 weeks later...
  • 3 weeks later...
FriendshipUSA New Member

FriendshipUSA

Posted
Posted

I changed the o2 sensor today. It now idles, but it fluxuates between 500 and 1000 RPM. I am believing it just might be that darn cat. It is hesitating from a dead stop and during acceleration when I am below 40-45 MPH. :)

 

 

 

 

Just a thought: the vintage GMC truck I have once developed a cat problem. I was about 80 miles from home and limped it back home. A friend diagnosed the problem immediately. He suggested to run the truck with the front o2 sensors be removed. The truck regain the lost power (but was very noisy). The cat and muffler were then replaced and the problem was solved. I would suggest this test be run by someone who might know how the on-board computer will handle the o2 sensors removed. If it is something that might work, then, test the truck in a cold state w/o the o2 sensors in it.

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