jfz80
Cruisin’
Ok so truck is two hours from me and I spent the last two days working on it to no avail. I am home briefly to do some searching/regrouping and will be heading back asap to tackle it this week. sorry for the long post but trying to be thorough and brief as possible.
background:
1990 gmc TBI 5.7. SM420 Daily driver 10k miles a year. Leaks
I purchased the truck in 09. The 350 has been in place for over 10 years and has driven fine while I have owned it minus an alt. snafu.
THERE IS NO CEL-- as in not installed, anywhere, not just unlit
This makes codes hard to come by unless I get the ALDL cable interface for a laptop or someone knows which circuit I could tie a light bulb into to read. The OBD1 readers just flash your CEL to get the codes just like jumpering the ALDL but again there is not CEL lamp.
Issue:
Drove fine all last week. Filled up friday morning and noticed a fuel smell while driving b/w meetings around town. Checked lines/unions/filter/pump for leaks and there were none. 5pm friday traffic and it began to stumble and idle dropped and stalled at a red light. Pushed to safety and could not start. It turns over fine, fires, then promptly dies. Fuel pump was making a whining noise that was new at this time. A day later I was able to get it started and keep it running by feathering the gas and keeping revs up. bucked horribly under load in 1 and 2 but once up to hwy speed did pretty good with exception of lack of power(stumble under load) max speed of 60 and fuel smell. Longer it ran better it drove but didnt have the confidence for 2 hrs of hwy.
Actions so far:
Not a fan of shotgun approach mostly for the price of the ammo but stuck out of town limits your options. So far I have done the following.
New fuel pump-- electrical 25-30 psi-- replacement for part that had been installed and working since purchase
*edit* seems the clerk was looking at the wrong specs..... google shows 5-9 psi for this unit**
New Fuel filter
New injectors in TB (old were corroded and had odd spray pattern)
Replaced all gaskets/seals/diaphragms in TBI unit as well
Replaced all vacuum lines and even the plugged port caps too.
New intake manifold gaskets (mostly to fix the leak) Tstat/dizzy too
New coil
New Distributor/ecm/cap rotor (old tested fine but was horribly corroded)
set base timing to zero with set timing plug disconnected, reset ecu
Tested TPS-- in spec .534 closed and 1700 open
Tested IAC-- jumpered ALDL and can hear and feel IAC plunger move in the tb-- could not verify its travel but could feel it open close
Tested EGR by applying vacuum and diaphram moves freely
Tested MAP sensor with vacuum and it reponds to different levels
The truck starts and runs great untill it warms up. Then the idle begins to slow and eventually it stalls. I advanced the timing to 4 then 6* and it would run better with greater throttle response (less delay) however it was not driveable. It runs fine but when under slightest load (like disengaging clutch 1/2/3rd gear) it bucks/surges horribly. Strangely and maybe unrelated it drove quite well in reverse.
My thoughts:
really Im out of good ones, hence the borrowed car and long post
IAC has not been replaced and I have read multiple times a failed IAC will cause the fuel pump to go out. However my pump just sounded horrible yet seemed to provide plenty of fuel, replaced it for the previously broken and rigged + terminal. I can hear IAC activating in the tb and stuck a pick down there to make sure the plunger was actually moving and it was. Still a suspect in my mind
Cooant temp. sensor? maybe affecting the ECU with wrong temp data? Especially since it occurs after warm up or enriching cycle.
Any and all help very much appreciated guys
background:
1990 gmc TBI 5.7. SM420 Daily driver 10k miles a year. Leaks
I purchased the truck in 09. The 350 has been in place for over 10 years and has driven fine while I have owned it minus an alt. snafu.
THERE IS NO CEL-- as in not installed, anywhere, not just unlit
This makes codes hard to come by unless I get the ALDL cable interface for a laptop or someone knows which circuit I could tie a light bulb into to read. The OBD1 readers just flash your CEL to get the codes just like jumpering the ALDL but again there is not CEL lamp.
Issue:
Drove fine all last week. Filled up friday morning and noticed a fuel smell while driving b/w meetings around town. Checked lines/unions/filter/pump for leaks and there were none. 5pm friday traffic and it began to stumble and idle dropped and stalled at a red light. Pushed to safety and could not start. It turns over fine, fires, then promptly dies. Fuel pump was making a whining noise that was new at this time. A day later I was able to get it started and keep it running by feathering the gas and keeping revs up. bucked horribly under load in 1 and 2 but once up to hwy speed did pretty good with exception of lack of power(stumble under load) max speed of 60 and fuel smell. Longer it ran better it drove but didnt have the confidence for 2 hrs of hwy.
Actions so far:
Not a fan of shotgun approach mostly for the price of the ammo but stuck out of town limits your options. So far I have done the following.
New fuel pump-- electrical 25-30 psi-- replacement for part that had been installed and working since purchase
*edit* seems the clerk was looking at the wrong specs..... google shows 5-9 psi for this unit**
New Fuel filter
New injectors in TB (old were corroded and had odd spray pattern)
Replaced all gaskets/seals/diaphragms in TBI unit as well
Replaced all vacuum lines and even the plugged port caps too.
New intake manifold gaskets (mostly to fix the leak) Tstat/dizzy too
New coil
New Distributor/ecm/cap rotor (old tested fine but was horribly corroded)
set base timing to zero with set timing plug disconnected, reset ecu
Tested TPS-- in spec .534 closed and 1700 open
Tested IAC-- jumpered ALDL and can hear and feel IAC plunger move in the tb-- could not verify its travel but could feel it open close
Tested EGR by applying vacuum and diaphram moves freely
Tested MAP sensor with vacuum and it reponds to different levels
The truck starts and runs great untill it warms up. Then the idle begins to slow and eventually it stalls. I advanced the timing to 4 then 6* and it would run better with greater throttle response (less delay) however it was not driveable. It runs fine but when under slightest load (like disengaging clutch 1/2/3rd gear) it bucks/surges horribly. Strangely and maybe unrelated it drove quite well in reverse.
My thoughts:
really Im out of good ones, hence the borrowed car and long post
IAC has not been replaced and I have read multiple times a failed IAC will cause the fuel pump to go out. However my pump just sounded horrible yet seemed to provide plenty of fuel, replaced it for the previously broken and rigged + terminal. I can hear IAC activating in the tb and stuck a pick down there to make sure the plunger was actually moving and it was. Still a suspect in my mind
Cooant temp. sensor? maybe affecting the ECU with wrong temp data? Especially since it occurs after warm up or enriching cycle.
Any and all help very much appreciated guys
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