I may have opened up a can of worms that I can't close.....and asking this question may be opening another, but I am worried I may have caused severe internal engine damage.

I changed out my copper Delco cr43ts plugs for platinum autolite ap25. I feel stupid for doing it now, but I wanted a plug that was going to last a little longer. I didn't have the understanding of heat range that I do now. A week later my truck died in traffic and it hasn't started since. It has spark and fuel, cranks, turns over and stalls immediately.

I did a compression test, five of the cylinders read between 120 and 135 psi, but cylinder 5 read 90 psi. I gave it a squirt of oil and the next reading was 190 psi. Could the 100 miles I drove that week with platinum plugs burn up my piston rings? Would it be worth the time and money to have a leak down test done, or would they end up telling me its the rings? Would the low compression on cylinder 5 prevent the truck from running? I can start the engine with my foot on the gas to make it run, it shakes the truck around until I let it go, then stalls.

the truck has a new battery, alternator, fuel pump, pick up coil, cap and rotor, ignition switch, and in the last year I have changed out the ignition coil, wires, egr, and starter.

I haven't pulled an engine out yet, but I knew it would happen someday, I just want to be sure it is absolutely necessary I have to before I do it.

I would appreciate any constructive suggestions.

thanks guys

 

If it were me I would check the ecm and prom chip first and make sure both are working correctly. Second I would check all vacuum lines, grounds and ensure everything is where it should be. While I am unsure about heat ranges on specific spark plugs I do know a friend who installed the new ac delco iridiam plugs with no problems. I myself run Bosch platinum four with no issues.

 

thanks Hans

Do you know of a way to test the ECM and PROM? I pulled mine out to look at it, without really knowing what I was looking for. The case had some corrosion on the outside, on the small plate covering the PROM and screw holding it in place. It looked ok on the inside, didn't smell like burnt electronics, it smelled like it had been shoved up inside a dashboard for the last 23 years.

It still gives me a code 12 when I ground the ALDL. It gave me a MAP sensor code when it was unplugged, and once it gave me a VSS code but the manual said to disregard that code if the vehicle had not moved. Could the ECM and/or PROM be bad if it is still storing codes?

I have been over all the vacuum lines, replaced some in the last year, they appear to be in good shape. Set and reset TDC on cylinder one several times, hoping I was off the last time I set it.

Thanks for checking it out

 

Code 12 is Power On Self Test for obd1.

 

IMO platinum plugs did not cause your problems - I have run plats in all three of my gas burners for a long time now with no problems - we also have two VW buggys that plats are the only plugs that we get any time of run time out of at all - even with # 5 a little low on compresion it still should run - might miss a little but will still run - with no codes showing I would do the normal tests such as fuel pressure

 

The best way to check the ecm is with a code reader. Most auto parts stores should have one that you can use to check your ecm and prom chip with. Also keep in mind that the ecm is also located under the heater core and leaks from the heater core can damage the ecm and prom chip.

 

Code 12 is just the ECM saying it is on and working, right? If the ECM wasn't working or storing codes, it wouldn't flash 12 when I jump the diagnostic port, right?

The truck has OBD I and autozone can only read OBD II, do any of the other parts stores read codes? I thought that was autozone's thing. But I can't get the truck started, so it doesn't really matter.

The heater core was leaking two years ago, and I repaired it at the time. Last week I pulled out the ECM to have a look, it has some corrosion from liquid on its exterior case, right on the small cover for the PROM chip. It looks like a little bit got inside and stained the circuit board. I have another truck with the same ECM but a different Prom chip, I pulled that one out last night and switched them all around, and tried the different ECM with the same PROM chip, same results. It appears to be the origional chip, it is stamped Delco, while the oter trucks isn't, it may have been changed out before I bought it. I looks like I can get a new ATBA PROM chip for $70, I might go ahead and try it because I have already tried all of the other sensors and switches I could think of.

 

Check fuel pressure. should be 10-15PSI for a throttle body engine. just because it sprays doesn't mean its enough fuel. will it run with carb spray? you said you've checked #1 TDC. Since this happened? Cam timing jumped a tooth maybe? fuel and spark gotta b timing.