1991 Chevrolet Cheyenne 1500 Engine pinging and high idle

Discussion in 'Chevy C/K Truck Forum' started by coop.s, Feb 15, 2014.

  1. coop.s

    coop.s New Member

    Hello everyone. My name is Steve and I am a new member to the site, but I have been lurking for quite some time and I've gained alot of good info from this site. I am hoping that maybe someone here will be able to help me, I'm just about at wits end with this problem. Here's the story: I bought this truck a few months ago and since then have done alot of work on it. The first issue I had on the way home was the heater not blowing hot, installed a thermostat, problem solved. The very next day the idler pulley gave up and I replaced it. That same day I started hearing ALOT of pinging, I replaced the spark plugs, wires, cap and rotor. No Luck. A few days later I also installed a new knock sensor and pigtail. Due to the truck not wanting to start and run at idle when it was cold, I also replaced the Idle Air Control valve at the same time. The truck quit pinging but the idle was high (1500-1700 RPMs). After about 800 miles of ping-less driving, the ping has returned. I'm reminded of The Poltergeist here. When the ping first came back it was not very loud and did not sound too bad but it has grown to be really bad here as of late. Today I tested the Throttle Position Sensor with my multimeter and got a reading of .60 volts on the blue wire and 5.02 volts on the gray wire. The check engine light was on and it threw Code 22-Low Reading. The information I have found on the internet says that the blue wire should be between .65 volts and .68 volts and the gray wire should be at 5 volts. When I unplugged the TPS the idle went down to about 900 RPMs, I left it unplugged and drove into town to go get a new TPS. I installed the new TPS and it brought the idle to 1100 RPMs. I started home and the pinging was still alive and well. I stopped at a friends house and we tried to adjust timing, according to my friend the timing was advanced about 20*. So we adjusted it to where it was advanced at about 4*. It ran good and idled at 900 RPMs, so I shut it off and reconnected the wire to the distributor and fired it back up and it ran at 1100 RPMs and advanced the timing by 20*. While we were at it we checked the EGR valve by squeezing the diaphragm and it tried to stall the truck, I am told that this is a sign that the EGR valve is still good. I do not have access to a vacuum pump at this time to do any further testing on the EGR valve, if there are any other ways to test it, I'd be glad to try them. The EGR solenoid also seems to have a ton of vacuum on both ends. On the drive home the pinging persisted but it did seem quieter and not as bad. I am now sitting at my computer feeling defeated. Has anyone else ever had a similar problem, or can anyone give me any more insight on what I should test next? I've tried to list as much information as I can here and I'm sure I'm leaving something out.

    The only other parts I can think of are:

    Temperature Sensor near the water inlet-Can this possibly lead to pinging?
    MAP Sensor-How do I test it and could it play a role in the pinging?
    Fuel Filter-What is the likelihood of this leading to pinging?
    Fuel Regulator in Throttle Body-Considering putting a rebuild kit in the TBI although it does seem pretty clean in there (I've got a can of seafoam for tomorrow just to try)
    Then there is the possibility that my truck could be a very unhappy transformer....

    Please help...I'd hate to waste the gas just to drive it off a cliff...
  2. edsmagichands

    edsmagichands Member 2 Years 100 Posts

    Hi Steve. if you still need help post an update of anything else you've done, along with engine size, i have a couple of ideas for you.

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