Jazzguitar67
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Hello....this is my first post here, thanks in advance for any help you can provide.
Back in February, I bought a 96 K1500 GMC Suburban w/ a 5.7L Vortec engine and 145,000 miles. The truck is in overall great shape with no rust, a clean interior and it had been running very well. I should say that in the 12 months before I bought the truck, the previous owner only put 3,000 miles on it.
A few weeks ago, after driving the truck for about an hour and starting from a traffic light up a long hill, the check engine light went on and the truck started to sputter under acceleration.
We finished our trip and the next day I jumped into the truck to go to Autozone to have a scan tool put on it. By the time I got there, the Check Engine light went out and the truck starting running normally. I did have them put the scan tool on it and it registered a PO300 code.
For the next two weeks or so, the truck drove perfectly.
This past weekend, I loaded the family in the truck and headed off for a trip. At exactly the same traffic light, the Check Engine light came on again and the truck sputtered up the hill and for the next two hours driving it.
The next morning, the truck started fine and no Check Engine light came on. It drove great for two days. Then, we loaded up and headed for home. After driving for about 40 minutes, we came to another steep hill. The Check Engine light came on and the truck continued to misfire for the next 2 hours. The misfire primarily occurred when applying heavy throttle. Just cruising, it seemed to run fine.
When the truck sputters, here is what happens: It revs like mad, but makes no power, 1st to 2nd gear shift is hard as hell -bangs into gear!(trans is smooth when not mis-firing) there is surging in acceleration and, even at full throttle, it loses speed going up steep hills.
I did some research on the PO300 code and found it could be fuel, spark or mechanical issues (like a bad intake gasket). I decided to start with fuel first, as it seemed the most easy to address.
I rented a fuel pressure gauge from Autozone. I took the reading at the fuel rail and it registered 52PSI. Since I don't know when the fuel filter was last changed, I decided to start there. I put a new fuel filter on, put Seafoam in the tank and tested the pressure again. The gauge still reads 52PSI.
I understand that the spec on fuel pressure should be between 60-66psi. The thing is, I have seen all sorts of threads about what can cause low pressure-fuel pumps, pressure regulators, poppet valves, etc.
What I can't figure out is how to troubleshoot what my exact problem is. Before I put a new pump (or pressure regulartor, etc) in the truck, I would like to try to sort out how to figure out how to get pressure up to spec.
When the filter came off, the gas that came out was dark grey (dirty). After installing the filter, the truck drove like crap for about an hour. Then, the check engine light went off and the truck drove relatively smoothly. I drove it for an hour this morning and it drove well, but fuel pressure is still registering 52 psi.
I will eventually move on to tuning her up-new cap & rotor, plugs, wires, PCV valve. For now, I want to solve my fuel pressure problem before moving on.
Can anyone give me some advice on how to systematically troubleshoot this issue?
Thanks,
Drew
Back in February, I bought a 96 K1500 GMC Suburban w/ a 5.7L Vortec engine and 145,000 miles. The truck is in overall great shape with no rust, a clean interior and it had been running very well. I should say that in the 12 months before I bought the truck, the previous owner only put 3,000 miles on it.
A few weeks ago, after driving the truck for about an hour and starting from a traffic light up a long hill, the check engine light went on and the truck started to sputter under acceleration.
We finished our trip and the next day I jumped into the truck to go to Autozone to have a scan tool put on it. By the time I got there, the Check Engine light went out and the truck starting running normally. I did have them put the scan tool on it and it registered a PO300 code.
For the next two weeks or so, the truck drove perfectly.
This past weekend, I loaded the family in the truck and headed off for a trip. At exactly the same traffic light, the Check Engine light came on again and the truck sputtered up the hill and for the next two hours driving it.
The next morning, the truck started fine and no Check Engine light came on. It drove great for two days. Then, we loaded up and headed for home. After driving for about 40 minutes, we came to another steep hill. The Check Engine light came on and the truck continued to misfire for the next 2 hours. The misfire primarily occurred when applying heavy throttle. Just cruising, it seemed to run fine.
When the truck sputters, here is what happens: It revs like mad, but makes no power, 1st to 2nd gear shift is hard as hell -bangs into gear!(trans is smooth when not mis-firing) there is surging in acceleration and, even at full throttle, it loses speed going up steep hills.
I did some research on the PO300 code and found it could be fuel, spark or mechanical issues (like a bad intake gasket). I decided to start with fuel first, as it seemed the most easy to address.
I rented a fuel pressure gauge from Autozone. I took the reading at the fuel rail and it registered 52PSI. Since I don't know when the fuel filter was last changed, I decided to start there. I put a new fuel filter on, put Seafoam in the tank and tested the pressure again. The gauge still reads 52PSI.
I understand that the spec on fuel pressure should be between 60-66psi. The thing is, I have seen all sorts of threads about what can cause low pressure-fuel pumps, pressure regulators, poppet valves, etc.
What I can't figure out is how to troubleshoot what my exact problem is. Before I put a new pump (or pressure regulartor, etc) in the truck, I would like to try to sort out how to figure out how to get pressure up to spec.
When the filter came off, the gas that came out was dark grey (dirty). After installing the filter, the truck drove like crap for about an hour. Then, the check engine light went off and the truck drove relatively smoothly. I drove it for an hour this morning and it drove well, but fuel pressure is still registering 52 psi.
I will eventually move on to tuning her up-new cap & rotor, plugs, wires, PCV valve. For now, I want to solve my fuel pressure problem before moving on.
Can anyone give me some advice on how to systematically troubleshoot this issue?
Thanks,
Drew
