Low on power & pinging

wtdwtd Member Posts: 96
edited March 2014 in Chevrolet
Within the last three weeks, My 98 chevy ext-cab Z-71 with 33,500 miles has lost power and is now pinging under load. I changed the fuel filter to no avail. Checked spark plugs but they were still good. I checked for vacumn leaks but couldn't find any. I checked fuel pressure and at idle it reads 54psi. I reved it up real quick and it goes to 62 psi, than drops back to 54psi. When you partially turn key to activate fuel pump it goes up to 61 psi and than drops down. Factory helm service manual says fuel pressure should be 60-66 psi with pump on and motor off. Says it should jump up to about 66psi when you rev the motor real quick. Mine only goes to 62psi. Could I have a fuel pump problem? My pump has also gotton alot quieter than it used to be. Can anyone tell me what elso I should look at to fix this problem? I do not get a SES light and no codes are stored on the computer. No misfires or anything. Truck feels like it has a restriction. You give it gas but it hardly picks up any speed. Gas milage has also suffered. Thanks for any ideas.



  • mastermechanicmastermechanic Member Posts: 31

    Did you go though the troubleshooter diagnostics in your Helm? I had the same problem, but I was unable to connect a fuel pressure guage to the return line, so I rigged up a rubber hose to the fuel pressure gauge, I dropped the gas tank and connect the other of the rubber hose to the out pipe of the fuel tank. My problem was a bad fuel pump. It was under warranty, so no problem.

    My fuel pressure is regulated by the need of fuel. My Helm book informs me that deviation of a few pounds is ok
    You could have bad injectors. You need an injector tester find out. If your book tells you that one of the problems could be a leaking injector and that you need to pull all of them out by the rial, turn on the key, and see if any of them leak, do this first, because this would point to your problem.

    I don't know where you are at, but some places like Murray's rent them at no change.

    What is your oil pressure like? It can affect your performance. You need to do the diagnostics.

  • Mr_ShiftrightMr_Shiftright Member Posts: 64,482
    I'd go along with MM....bad injectors seem like a plausible explanation for this condition.

    MM--would you please not include your logo in all your posts? thank you!

    Mr. Shiftright
  • blackgtpblackgtp Member Posts: 19
    Low Power and less MPG. The first and easiest thing to check is the air filter. Also, do you have a carbon problem? You might think about running some engine cleaner through it. Just some ideas. It's always hard to diagnose on the computer.
  • Mr_ShiftrightMr_Shiftright Member Posts: 64,482
    air filter wouldn't cause pinging though.
  • blackgtpblackgtp Member Posts: 19
    Mr. Shiftright

    I hope my post didn't infer that it would. It may or may not be one problem.

    wtd - Have you checked for an exhaust restriction?
  • alcanalcan Member Posts: 2,550
    Pinging (or spark knock), more accurately referred to as pre-ignition or detonation is the sound made by 2 flame fronts colliding in the combustion chamber. It's generally related to high combustion temperature. Possible causes can include:
    lean fuel mixture
    EGR system malfunction
    high compression ratio due to carbon buildup in combustion chambers
    knock sensor malfunction
    over-advanced ignition timing
    high engine temperature
    low octane fuel

    Severe detonation WILL eventually blow holes through the aluminum piston crowns.
  • oldharryoldharry Member Posts: 413
    and pinging. Try a compression check, if all cylinders are low it is likely a timing chain. We replaced a lot of them in the sixties, but it seems to be an unusual problem now.

  • wtdwtd Member Posts: 96
    Well, I replaced the fuel pump and my pressure was the same so it wasn't that. I also replaced the two O rings that are on the fuel lines that go into the fuel filter and replaced the gas cap and the truck seemed to gain some power back. I also used a can of the spray version of GM top engine cleaner which seemed to help the pinging. Truck still seems a little sluggish but not as bad as before. Gas milage is still worse than before.

    Getting to the fuel injectors on this truck is kind of a hassle since my intake manifold is a two piece affair with the fuel injectors and fuel regulator under the top section. With such low milage, its hard for me to believe that the injectors might be bad already. I havn't checked the fuel pressure since replacing the two O rings and gas cap so I don't know if it increased.

    My air filter is brand new and I had the catalytic converters checked for restrictions which were not restricted. EGR valve checked out okay. Timing is non adjustable on this truck since it uses a cam and crank sensor to control timing. Knock sensor seems okay as it hasn't set any codes. There are no codes of any kind and the SES light has not come on.

    I'm going to run a bottle of Chevron Techron fuel system cleaner through the next tank of gas and see what happens.

    I still think it may be a fuel pressure problem, since the pressure is less at idle than the Helms manual says it should be. Fuel regulator may be not working right. Any other ideas?

  • Mr_ShiftrightMr_Shiftright Member Posts: 64,482
    I've personally witnessed bad injectors on a very expensive car with only 100 or so miles on it. It's certainly possible.
  • jgmilbergjgmilberg Member Posts: 872
    It could be a bad O2 sensor, I would have never found it w/o using a scan tool. It stuck in a normal operating range and never varied like it was supposed to. The result was no SES light and no trouble codes. It cured the problem I had with my S-10 4.3L, it sounds like the same thing yours is doing.

    The O rings will not help your fuel pressure problem unless they were leaking. It could be a defective regulator.
  • wtdwtd Member Posts: 96
    I have a scan tool and have monitored all four of my O2 sensors. The pre-cat sensors scan up and down pretty fast like they sould. The after cat sensors stay at a pretty solid reading after the truck warms up except one stays at about 0.645v and the other at about 0.175v. I don't know if they are supposed to be close to the same or not. I'm pretty sure they are not supposed to scan up and down like the front two. My exhaust pipes are very black, so I'm running rich, but I'm not sure what is causing it.

    Truck has again lost power, so I guess I'll have to try and get an injector and regulator test done. I'm getting pretty discouraged with this whole thing.
  • jgmilbergjgmilberg Member Posts: 872
    The front three should scan up and down like crazy. Just to make sure we are on the same page, one sensor is for the left bank, one for the right, one pre cat common in the Y-pipe, and one 3-6 inches after the cat. The after cat one is usually pretty stable after warm up, the other 3 should continue to jump around, this will constantly make the truck adjust the air/fuel mix. The one before the cat is supposed to be the left and right banks combined, and almost overrides the other two, the one after is supposed to be the "clean" air reading and will not move as crazy as the before and it will also read considerably lower than the front set.

    I have had the same thing happen to me on a Dodge van 318. Kept racking my brain took it in to a small shop they couldn't figure it out, took it to the dealer it was the ignition coil. After hours of time looking for the problem, and lots of money thrown at it, it turned out to be a simple $25 part. Wouldn't set a trouble code, and voltage tested fine, but it had a small crack in it, and when it warmed up it would arc to ground instead of the plug. Your problem may also be caused by a faulty ignition module, the one under the distributor cap, I had a Le Sabre do that to me once, but after a while it would stall out, and not re-start for 20 minutes.

    Out of curiosity have you checked the Manifold Air Pressure and Manifold Air Flow sensors?

    Other things to check are ALL ground wires, to the engine, frame, battery, and ECM. Knock sensor circuit. Charging System output. EGR valve function.

    If all else fails check this site plug in your VIN and see if there is an update for your ECM programming. http://vci.ecomm.gm.com/vci/
  • wtdwtd Member Posts: 96
    Well, earlier tonight I went out and decided to recheck my plug wires. I did this in the total darkness of my garage with the bulb out of my underhood light. After the truck warmed up, I could see arching from the end of the spark plug boots to the block on all cylinders. Some of the wires on the drivers side were arching in some places. Occasionally I could see an arch from my coil to the coil bracket. I guess this could be my problem all along. What do you think? Time for new plug wires and coil?
  • seeligseelig Member Posts: 590
    you obviously have spark, so coil (or coils, '99 and later) are probably fine. be sure to use some "Dielectric" grease on the boots to prevent arching.
  • jgmilbergjgmilberg Member Posts: 872
    You need to replace the wires. I would be willing to be they are cracked and leaking, giving you the arcing from the boots, and wires. I have had the best luck with Accel brand 8.8mm wires, most auto zone stores carry them, here is a link to the site where you can locate a dealer near you. http://www.mrgasket.com/deal.htm If you decide to go with stock wires then DO NOT CHEAP OUT!!! A crummy set of wires,like Cobra line will leave you stranded when you least expect it, and they do not last as long. The only other brand wire I would trust would be AC Delco. You may also consider changing your distributor cap and rotor, but with your mileage you probably won't really need to. Dielectric tune up grease is highly recommended also, it will keep the boots from sticking to the plugs, and will also help keep them from cracking.

    Keep us informed.

  • seeligseelig Member Posts: 590
    go for the best.....Magna Core......if you really want the best then i'll email you the info.
  • wtdwtd Member Posts: 96
    the plug wires, spark plugs, coil, cap & rotor and the truck runs much better. I went with AC-Delco on all replacements because I needed to get the truck running right and didn't want to wait on ordering parts. The coil had two spots on the side of the body where the spark was arching through. One spot was pretty big. Spark plugs looked pretty dirty, probably from the top engine cleaner I had used, and one of the platinum discs on the top electrode was gone. I initially didn't replace my cap & rotor because I had just replaced them 7,000 miles ago, but I talked to someone pretty knowledgeable on these trucks and said that all of the arching wires and the coil probably caused some cross firing in the cap and that it needed to be replaced. After test driving the truck with just the new plugs, wires and coil, it still felt sluggish. After putting on the cap & rotor, the motor felt much stronger so he might have been right.

    Truck had started pinging again about a week ago and even with all of the new parts, it still pings a little bit. I guess I will have to live with it since I don't want to spend anymore money on it right now. Replacing all of these recent parts along with the fuel pump has set me back over $500. I just hope this thing is fixed.

    I want to thank everyone who gave information and advice.

This discussion has been closed.