Can someone solve this problem?
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Member
Joined: Jul 2002
Posts: 203
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From: East Los
Can someone solve this problem?
This is for some hometown at another forum. He really needs the help. He says its stock '94 GMC 5.7L TBI
-ron
-ron
First off this is on my SWMBO's GMC (3/4ton 5.7 4spd auto 123k miles)
This thing is killing me.
About a week or 2 before we moved from Co to ND it started acting bizarre, getting slightly worse and worse mileage, a tad gutless, but NO codes. It took 3x more gas to get to ND then it had taken us to move down to CO.
History:
Last December the TPS went out and threw code 22 (it was an excellent time for me to buy a GM EFI book) and I replaced it and all was good (for a week or so) then it threw code 23 and 22 (MAP and TPS) apparently I had forgotten to plug the MAP vacuum hose back in AND clear the resident codes.
This spring I did the 100k tuneup on it (just a tad late) plugs,air filter, O2 sensor (3wire style), cap/rotor and the oil pressure sending unit because it was acting funny. Then still during this spring she had a heater hose fitting corrode off the intake (woot for the GM aluminum). So I got to replace the intake with a junkyard peice because the threads were really messed up due to GM putting an aluminum fitting into an aluminum manfold. But then it ran perfect again.
Until we went camping up at Steamboat Lake CO (35 miles North of Steamboat Springs the town) when the coil went bad. The computer does not throw codes for fuel delivery or spark delivery so I got lucky and mooched a ride back to town with a lady and bought a reman dist (returned later) a coil, and some tools (why didnt I bring some??)
But that's it, 10yrs of service it has been in her ownership since 7 miles on the odometer and now its doing this..
It actually runs pretty well when its cold (temp sensor?) For a while it was slamming into gear (same behavior as TPS sensor out EXCEPT no code) but gutless. When you push the gas it seems to have no accellerate from coast power until you press the gas pedal enough to kick it down a gear then it accellerates normally. My SWMBO describes it as "acting like it has a turd up its tailpipe".
I replaced the TPS (again, 2nd time in 7months only 3month warranty) and the harsh shifting went away but the power is still non-existant. If it had a check engine light on I would run it directly over to a shop for a scan but without one they will still charge for the work before looking for the problem ($20 independant shops, $45 at dealership) I have talked to several people and did some reading (I at least looked at the pictures)
Poor Mileage is caused by things like
EGR malfunctioning
MAP sensor reporting improperly
Plugged exhaust (catalytic converter)
the EGR seems to move freeley and when I applied vacuum to it the diaphram moved (engine not running, me sucking on the hose) And when I manually opened the EGR when the engine was running it slows down considerably and the engine starts to miss and studder.
I took it to an exhaust shop for the Catalytic converter they said all they do is measure incoming temp vs out going temp and "hit it with a hammer to see if anything is loose in it" They gave it a "pass", but I sure would like a more conclusive test.
The MAP sensor I took out the multi-meter and determined which wire was the ground, then which was the 5v reference from the ECM, then probed the return line. At idle it was 1.45v when I sped it up slightly (cant see the tach from under the hood) the voltage dropped to 1.15v, and kind of hovered around 1.20v. I shut off the motor and used my self vacuum technique again and got it to move from 4.65v down to .5v, not real scientific but I dont have a vacuum pump.
Other things that I have been told to check out, ECM temp sending unit (reporting constant "cold"), one shop said that if my fuel pump was getting weak it could contribute to increased fuel consumption (I dont understand that one fully with INCREASED fuel consumption).
Timing chain could be getting stretched after that many miles but I would think that shouldnt have as much affect on the fuel consumption and sluggishness. Maybe I will have one of the Autoparts stores scan it for me (one of those "free" services) just to be sure.
The worse part of this whole ordeal is that starting tomorrow she will be driving MY mustang until I get HER pickup fixed.
Any thoughts, ideas are appreciated
if you see any oversights let me know
i need help
-ron
This thing is killing me.
About a week or 2 before we moved from Co to ND it started acting bizarre, getting slightly worse and worse mileage, a tad gutless, but NO codes. It took 3x more gas to get to ND then it had taken us to move down to CO.
History:
Last December the TPS went out and threw code 22 (it was an excellent time for me to buy a GM EFI book) and I replaced it and all was good (for a week or so) then it threw code 23 and 22 (MAP and TPS) apparently I had forgotten to plug the MAP vacuum hose back in AND clear the resident codes.
This spring I did the 100k tuneup on it (just a tad late) plugs,air filter, O2 sensor (3wire style), cap/rotor and the oil pressure sending unit because it was acting funny. Then still during this spring she had a heater hose fitting corrode off the intake (woot for the GM aluminum). So I got to replace the intake with a junkyard peice because the threads were really messed up due to GM putting an aluminum fitting into an aluminum manfold. But then it ran perfect again.
Until we went camping up at Steamboat Lake CO (35 miles North of Steamboat Springs the town) when the coil went bad. The computer does not throw codes for fuel delivery or spark delivery so I got lucky and mooched a ride back to town with a lady and bought a reman dist (returned later) a coil, and some tools (why didnt I bring some??)
But that's it, 10yrs of service it has been in her ownership since 7 miles on the odometer and now its doing this..
It actually runs pretty well when its cold (temp sensor?) For a while it was slamming into gear (same behavior as TPS sensor out EXCEPT no code) but gutless. When you push the gas it seems to have no accellerate from coast power until you press the gas pedal enough to kick it down a gear then it accellerates normally. My SWMBO describes it as "acting like it has a turd up its tailpipe".
I replaced the TPS (again, 2nd time in 7months only 3month warranty) and the harsh shifting went away but the power is still non-existant. If it had a check engine light on I would run it directly over to a shop for a scan but without one they will still charge for the work before looking for the problem ($20 independant shops, $45 at dealership) I have talked to several people and did some reading (I at least looked at the pictures)
Poor Mileage is caused by things like
EGR malfunctioning
MAP sensor reporting improperly
Plugged exhaust (catalytic converter)
the EGR seems to move freeley and when I applied vacuum to it the diaphram moved (engine not running, me sucking on the hose) And when I manually opened the EGR when the engine was running it slows down considerably and the engine starts to miss and studder.
I took it to an exhaust shop for the Catalytic converter they said all they do is measure incoming temp vs out going temp and "hit it with a hammer to see if anything is loose in it" They gave it a "pass", but I sure would like a more conclusive test.
The MAP sensor I took out the multi-meter and determined which wire was the ground, then which was the 5v reference from the ECM, then probed the return line. At idle it was 1.45v when I sped it up slightly (cant see the tach from under the hood) the voltage dropped to 1.15v, and kind of hovered around 1.20v. I shut off the motor and used my self vacuum technique again and got it to move from 4.65v down to .5v, not real scientific but I dont have a vacuum pump.
Other things that I have been told to check out, ECM temp sending unit (reporting constant "cold"), one shop said that if my fuel pump was getting weak it could contribute to increased fuel consumption (I dont understand that one fully with INCREASED fuel consumption).
Timing chain could be getting stretched after that many miles but I would think that shouldnt have as much affect on the fuel consumption and sluggishness. Maybe I will have one of the Autoparts stores scan it for me (one of those "free" services) just to be sure.
The worse part of this whole ordeal is that starting tomorrow she will be driving MY mustang until I get HER pickup fixed.
Any thoughts, ideas are appreciated
if you see any oversights let me know
i need help
-ron
Member
Joined: Mar 2002
Posts: 266
Likes: 0
From: Coushatta LA
Check the timing, be sure to unplug the timing connecter(tan wire with black stripe) located inside the cab,pass side floorboard,under the glove box and set to 0º.
Fuel pressure is critical, the pump could be going south.
Fuel pressure is critical, the pump could be going south.
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