I am helping my neighbor with his 97 Blazer, 4x4, about 130K miles. His truck has been in the shop for the last month and none of the mechanics can figure it out. Only code is P0300, truck hesitates and is sluggish, rough idle.

So far, here is what has been done: New upgraded Spider injector assembly; EGR valve cleaned, tested and reinstalled; New distributor cap, rotor, plugs, wires, ignition coil, ignition module; new catalytic converter; and I think they tested fuel pressure. So far he has spent over $1200 and it still acts the same.

I cleared the code and we took it for a test drive. No light at first, but still hesitates. When I put it to the floor for a few seconds the SES flashed for a good 5-10 seconds then stayed on. Still only code P0300. What else can cause these symptoms? I'm going to check for play in the distributor gear to the cam. Can the crankshaft or camshaft sensor cause this without having a code for them?

Thanks and have a good one!

 

when you dd the ignition module did you put a healthy portion of dielectric grease on the heatsink to bracket surface and module to heatsink surface?

i did this on my 98 and it turned the truck into a whole new machine as far as throttle response in low rpms..

my guess is that the white pc grade thermal goo, after years it simply thins out too much and causes the module not to be as effectively cooled....

 

Yes, we used plenty of the good thermal grease. This one is stumping me, as well as 3 mechanics at the shop he took the truck to. I'm hoping to take a closer look at it tonight. I hope it's something as simple as the distributor gears or one of the sensors. I'm running out of ideas. Thanks and have a good one!

 

my truck had 86000 miles and had to have the distributor gear replaced after a tune up didnt cure a p0300. it was only slightly worn, but while you have it off and out might as well throw a new gear on. hopefully that will cure it.

 

The sensors would throw a code on top of the P0300.

I have the same exact problem that you have explained. Have you had the truck hooked up to the scanner and noted which cylinders are the ones misfiring? A decent scanner, like the one I used (Genisys), told me that cylinders 3+6 misfire consistently and equally. On a very rare occasion so would 1+4.

I have done the same things that you explained and my problem still has not been fixed.

The distributor itself could be bad. That's the only thing that I have yet to replace. There is a TSB on the distributor. It says that the shaft in the distributor can get rusty and it will cause the misfire. I took off my distributor and sure enough there was rust on the shaft. I would also spin it and I could hear it squeal. Hopefully that is the problem and the same could be with your neighbors.

 

Thanks, guys. Going to check the distributor first. Unfortunately, my neighbor has only owned the truck since last September so we don't have a good vehicle history. I will let you know what I find. Thanks and have a good one!

 

Sorry, guys, been a while. I had a kidney infection and the weather hasn't been cooperating. We changed the distributor out tonight, the gear was well worn, It does run a little better, but still not quite right. Under hard acceleration i tstill flashes the SES and then stays on. The only code is still P0300. This is stumping me, any help is greatly appreciated.

Thanks and have a good one!

 

did you do a case relearn on the new distributor and cam sensor?

Also, what's the compression on it? Did you make sure that there were no vacuum leaks?

 

I am not familiar with the case relearn, how exactly do you do that? I only have an OBD2 code reader, not one of the fancy scanners.

For the compression test, I did not run the test. that was done at the shop he took it to. They didn't list the exact values, but the mechanic told him that the readings were surprisingly good and were all close to one another. We checked for vacuum leaks and did not find anything obvious. Some hoses were in marginal shape, so we're going to replace a couple feet of hose first. It developed a coolant leak so have to replace the water pump first.

Thanks!