1998 Chev K1500 fuel pump

sleddineinar

sleddineinar

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Now I've got trouble with my truck. It seems that I have a fuel pump is going bad. My question is this. How should I go about testing the pump pressure. I know that the operating pressure should be 60psi. But I've never tested fuel pressure before. I'd like to make sure it's the fuel pump before I set down $300 for new pump.
 

If you have to ask than you dont have the proper gage as well as the right fittings to screw into the fuel rail.Its under the hood.


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More then a few auto chain stores offer "loaner tools", may or may not require deposit. Call around and see if any one has the gauge. I use an old air conditioning test set. The fitting threads onto the valve stem looking deal and stays there, you cant just bump it like checking air in a tire.
 
Here's the story... Last fall I had the SES light come on, the codes indicated a random misfire and a misfire on the #3 cyl. The #3 plug had a severely burnt electrode, I changed the plugs, the SES light went out. This winter the truck started to feel a single buck when accelerating up a hill or passing. Then in the spring I was heading up north with the snowmobiles and heading up hill with the cruise on, and I lost power, the RPMs went up, but my speed went down, from 75mph to 60. then at the top of the hill it cleared up. No codes at this time. It never did it again on the trip, but when I got home I replaced the fuel filter. Problem seemed to go away... then this summer it did it again. same thing as before. No codes again. Then a week later the SES light comes on truck is running rough. Same codes as I already mentioned. So thinking it might be electrical, I replaced the plug wires, dist. cap and rotor, they were very corroded. This time the #3 plug has no combustion residue, but the center electrode is burned way down. So I also bought a new plug, and a new poppet injector, replaced both. The injector was plugged and had crap built up on it. So the things seems fine until the other day, I take off from a light and no power. But problem persists, so that is why I'm thinking fuel pump.
 
before you replace the pump, try a new fuel tank cap. they are $15.00 locally so you should be able to get cheaper. sounds like the check valve in the cap is sticking and not letting air into the fuel tank. it is supposed to trip after it has a couple of inches of vacuum and when it is not acting properly, it does stuff like this. I replaced it 3 times on my 98 in the 10 years I owned it as it was the cheapest thing that would throw evap codes. bonus was that was usually the problem.
 
Some auto parts will also scan your truck for you as well, some are free and others charge for it. What are you running in it for fuel? I have a 95 1500 4x4 with the vortec 4.3 and it couldn't care less what octane I give it. My 98 2500 4x4 with the vortec 5.7 seems to have a stutter/stumble when running the cheap stuff from certain stations. I have heard some of the vortec 5.7s had/have issues with the intake gasket.
 
I normally run just 88 or 87. But the last fill I used 91. I've been running Lucas oil in it since I started noticing the studder. I drove it today and after driving for about 4 miles, that stumble showed up again. So I'll try a new gas cap.
 
The pump will generally get quite loud when its getting ready to go and it'll have a different whine to it. You should change your fuel filter every year on these trucks. If your intake manifold is leaking it'll randomly have some running issues and stalling along with getting coolant in the oil.
 
While these pumps do fail I have seen a number of pumps that were replaced when they didn't need to be. The testing procedures are quite straight forward and can be found in the Helm manuals (official service manuals) or at Alldata. You can also get the e-version on CD or online (Alldata is online). Once you get a fuel pressure gauge and attach it to the supply line (top right rear of engine) you really need to know the right testing procedure. There are several sensor inputs that are involved, so it is good to have the flowcharts as well. Based on what I have heard so far, I do not think it is a fuel pump. Basically this system supplies fuel at a certain pressure range to the centralized injectors where there is a manual regulator. The injectors are all located in a bank on the top center of the engine. Each injector has a vinyl output tube that goes to a single cylinder and has a poppet valve which extends into the intake port of the cylinder head. This system works good at first put can have problems as it ages. Because the atomization of fuel coming out of the poppet valves is not nearly as good as it is right out of the injector, the engineers had to extend the spray point into the intake port. Thus the face of the poppet valve can easily get gummed up if the engine fails to run properly. In other words, problems elsewhere can get compounded due to the design.

Here are some possible root causes . . .

- Distributor gear worn - generally indicated by CMP Correlation Error Code but not always
- Cap and Rotor worn or shorting out
- Bad spark plug wires
- Intake manifold leaking
- Low compression
- Clogged fuel filter
- Dirty injectors
- Broken or burnt poppet valve tubes
- Poppet valves burnt, sticking or gummed up
- Injector regulator failed
- Ignition module failed or not grounded properly
- Other sensors bad (giving invalid input)

What I like to do is use an OBD II pickup tool that will not only let you see the reading of each sensor but also allow you to log them and replay later. I still use my original AutoTap with GM extended codes. It captures sensor values 10 times a second into a log file on my laptop. I then can replay and analyze each sensor value over time. These values are the best info you can get about what is going on inside your engine (unless of course you are equipped with X-ray vision). Don't forget that something as silly as a faulty O2 sensor can wreak havoc on the fuel trim once it goes closed loop.
 
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So that didn't work either. Everything seemed fine until I took off for work. I got a couple miles down the road, stopped a at a light, and when I took off. Major stumbling! Even some backfiring!! I don't think I've ever had it backfire before. So turned around and got the car and went to work. BTW, no codes either.
 
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now I would check the pressure regulator as I have seen one fail. almost sounds like it is sticking open a bit.

on an aside note: have you cleaned and/or replaced the grounds from the cab to the motor or the motor to the frame? computer could be acting weird because the grounds are dirty or the cables are rotten. I did re-ground mine at one point for peace of mind and it did run better after.
 
So is the pressure regulator the little round doo-hicky on the side of the spider? No I haven't cleaned any of the grounds to the cab or the motor, but I will look at them when I have a chance. BTW, Thanks guys for all the helpful insights, really helping me chase this down.
 
last one I replaced was on a throttle body 4.3 in an s10. we found it by restricting the fuel return hose with a gauge on the fuel line.
 
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