1989 K3500 ran fine, now won't even stay alive without pumping gas pedal... Stumped.
June 26th, 2019, 7:24 PM
#12
CF Monarch
June 26th, 2019, 7:30 PM
#13
CF Monarch
Indeed so, but I WAS indeed mistaken as I thought the MAF unit did come on 1989 Chevy's, but they dont. I agree, lets get the OP's 1989 K-3500 pickup running properly again, Irish_alley...
June 26th, 2019, 10:09 PM
#14
Hello, new to the forum so please excuse any ignorance.
I bought an '89 K3500 (7.4L 454) last week and it was running great at first- I ran it up one of my local canyons to test the engine and experienced intermittent loss of power at high speeds, which got worse until the truck stalled out when I came to a stop. Was able to get it started, but it would only stay alive when I pumped the gas pedal. Weirdest thing. Was finally able to sputter it to the nearby Chevy dealership pumping the accelerator (oddly enough, the engine seemed to fire briefly when I let off of the accelerator, and I had to keep pumping to keep this up), and they ran a diagnosis and said that it has fuel pressure, but that the injectors were dumping fuel into the engine. Per their advice I replaced the injectors, plugs, plug wires, distributor cap/rotor, & ignition coil, and it still wouldn’t idle.
We then read the OBD and it said that there was an open circuit in the TPS sensor, so we replaced the connector and it still wouldn’t idle. When I took the TPS sensor out to replace, the screws were broken off inside the screw hole- but the strange thing is that the car still won’t idle or stay alive without me pumping the gas, and I don't believe you need a mounted tps to do either, as long as the arm is in the right place on the sensor.
I feel like we are one part or adjustment away from this thing running solid but need some advice from someone who knows the model better, because google has led me down multiple rabbit holes. Any suggestions on what to look at?
I bought an '89 K3500 (7.4L 454) last week and it was running great at first- I ran it up one of my local canyons to test the engine and experienced intermittent loss of power at high speeds, which got worse until the truck stalled out when I came to a stop. Was able to get it started, but it would only stay alive when I pumped the gas pedal. Weirdest thing. Was finally able to sputter it to the nearby Chevy dealership pumping the accelerator (oddly enough, the engine seemed to fire briefly when I let off of the accelerator, and I had to keep pumping to keep this up), and they ran a diagnosis and said that it has fuel pressure, but that the injectors were dumping fuel into the engine. Per their advice I replaced the injectors, plugs, plug wires, distributor cap/rotor, & ignition coil, and it still wouldn’t idle.
We then read the OBD and it said that there was an open circuit in the TPS sensor, so we replaced the connector and it still wouldn’t idle. When I took the TPS sensor out to replace, the screws were broken off inside the screw hole- but the strange thing is that the car still won’t idle or stay alive without me pumping the gas, and I don't believe you need a mounted tps to do either, as long as the arm is in the right place on the sensor.
I feel like we are one part or adjustment away from this thing running solid but need some advice from someone who knows the model better, because google has led me down multiple rabbit holes. Any suggestions on what to look at?
June 29th, 2019, 1:01 AM
#15
CF Monarch
The way I understand it the 94-95 model had higher fuel pressure specs and different injectors. You never know what could have been swapped into an old chevy or if you were given the wrong injectors. If all else fails I'd do my own pressure test and verify that's what the part number of the new injectors requires.
1989 7.4 liter fuel pump puts out 12 PSI.
1993 7.4 liter fuel pump puts out 29 PSI
1994 7.4 liter fuel pump puts out 40 PSI
1995 7.4 liter fuel pump puts out 60 PSI
The only thing I have found that would be a possibility is a clogged-up Catalytic Converter or some other exhaust restriction.
Last edited by oilcanhenry; June 29th, 2019 at 3:08 AM.
July 2nd, 2019, 10:59 AM
#17
Thank you to all for the help and advice, for some reason I wasn't receiving post notifications. Should be getting them now.
@Sabino56 , the truck is still in the same condition as it was right after it died- even after replacing those parts I mentioned. It will not stay alive unless I am pumping the gas pedal, and it almost appears that the injectors are spraying more fuel as they should when the accelerator is depressed, but for some reason there is no combustion unless I back off of the pedal, and then there is a very brief fire, requiring me to keep up that pumping motion to keep the engine alive.
It appears that the new injectors are working properly (spray pattern looks good) as the engine gets more gas BUT maybe not more air when I press the pedal- this is just a hypothesis, because there is more gas being given on depress, but the engine dies almost immediately.
Holding the accelerator down will cause a stall, and letting off of it will cause a stall. Very strange that the only time the engine will fire is for the quick second that I let off the pedal, and then I have to keep pumping to repeat that process.
I've made friends with the service manager at the Chevy dealership where it is parked right now (we found out we were born in the same hospital across the country) and he apparently ran his own engine building shop for many years, great guy, and appears to be very knowledgable about the engine. He's gonna come check it out today and bring some tools tomorrow to see if he can't figure it out outside of dealership labor rates.
Another thing worth noting is that the truck has some electrical issues. Sometimes the accessories remain on when I turn the truck off (I have to put the key back in, turn it to on, then back off to turn them off). The power windows do not work, and there are some wires hanging around the cigarette lighter areas. Not sure if this could be affecting the engine.
Thanks again for all the help, y'all. Between your and my friend's selflessness, I truly think that we can get her running this week given that she was running strong up until the sudden death climbing 3,000ft up the canyon.
@Sabino56 , the truck is still in the same condition as it was right after it died- even after replacing those parts I mentioned. It will not stay alive unless I am pumping the gas pedal, and it almost appears that the injectors are spraying more fuel as they should when the accelerator is depressed, but for some reason there is no combustion unless I back off of the pedal, and then there is a very brief fire, requiring me to keep up that pumping motion to keep the engine alive.
It appears that the new injectors are working properly (spray pattern looks good) as the engine gets more gas BUT maybe not more air when I press the pedal- this is just a hypothesis, because there is more gas being given on depress, but the engine dies almost immediately.
Holding the accelerator down will cause a stall, and letting off of it will cause a stall. Very strange that the only time the engine will fire is for the quick second that I let off the pedal, and then I have to keep pumping to repeat that process.
I've made friends with the service manager at the Chevy dealership where it is parked right now (we found out we were born in the same hospital across the country) and he apparently ran his own engine building shop for many years, great guy, and appears to be very knowledgable about the engine. He's gonna come check it out today and bring some tools tomorrow to see if he can't figure it out outside of dealership labor rates.
Another thing worth noting is that the truck has some electrical issues. Sometimes the accessories remain on when I turn the truck off (I have to put the key back in, turn it to on, then back off to turn them off). The power windows do not work, and there are some wires hanging around the cigarette lighter areas. Not sure if this could be affecting the engine.
Thanks again for all the help, y'all. Between your and my friend's selflessness, I truly think that we can get her running this week given that she was running strong up until the sudden death climbing 3,000ft up the canyon.
July 2nd, 2019, 11:05 AM
#18
That's a distinct possibility. and I am pretty sure you are correct about the change. I checked the specs for the new fuel pumps at Rock Auto and here what I found:
1989 7.4 liter fuel pump puts out 12 PSI.
1993 7.4 liter fuel pump puts out 29 PSI
1994 7.4 liter fuel pump puts out 40 PSI
1995 7.4 liter fuel pump puts out 60 PSI
The only thing I have found that would be a possibility is a clogged-up Catalytic Converter or some other exhaust restriction.
1989 7.4 liter fuel pump puts out 12 PSI.
1993 7.4 liter fuel pump puts out 29 PSI
1994 7.4 liter fuel pump puts out 40 PSI
1995 7.4 liter fuel pump puts out 60 PSI
The only thing I have found that would be a possibility is a clogged-up Catalytic Converter or some other exhaust restriction.
July 4th, 2019, 11:37 AM
#19
Well, I know the matrix inside the cat can fail and fall apart. I don’t know if it can be sudden death. I wouldn’t be surprised that it could happen suddenly.
As for pumping the throttle, I can’t understand why that would do anything on a TBI. It’s not like the carbs with a accel pump where you can pump gas into the engine by pumping the gas pedal. If you had a bad TPS, I could see where flipping the throttle might cause the TPS to send a good value to the ECM occasionally- but you replaced that.
I’m assuming the electrical problems were there before the sudden onset of current problem? If no, then that’s were to start. Electrical shorts can definitely cause problems.
Given you replaced the injectors and have a reasonable pattern, at least at idle it should be able to stay going. I would focus on the cat and stuff which effects timing. I think the questions on the MAP may have been aimed at that, but don’t know. I think you can diagnosis a cat looking at manifold vacuum but I’ve no experience on that. Maybe someone here knows.
As for pumping the throttle, I can’t understand why that would do anything on a TBI. It’s not like the carbs with a accel pump where you can pump gas into the engine by pumping the gas pedal. If you had a bad TPS, I could see where flipping the throttle might cause the TPS to send a good value to the ECM occasionally- but you replaced that.
I’m assuming the electrical problems were there before the sudden onset of current problem? If no, then that’s were to start. Electrical shorts can definitely cause problems.
Given you replaced the injectors and have a reasonable pattern, at least at idle it should be able to stay going. I would focus on the cat and stuff which effects timing. I think the questions on the MAP may have been aimed at that, but don’t know. I think you can diagnosis a cat looking at manifold vacuum but I’ve no experience on that. Maybe someone here knows.
