i got a "random multiple misfire" code after i replaced my crankshaft position sensor.... what it turned out to be was a bad crankshaft sensor...even tho it was new.

 

1999 Blazer LS, 153,000 miles, been an overall great truck to me since buying it new.

So, the problem is misses when getting up to 25 mph or holding steady highway speed at 65-70 mph (even with cruise).

What we've tried:
- Replacing two year old spark plugs
- New Wires, Cap, Rotor
- New Fuel Filter
- New O2 sensor
- New Catalytic Converter
- New MAS

My father mentioned a cleaning about running special injector cleaner directly into by removing the fuel lines. We may try that next. The fuel pump seems to be in good shape yet. What else could be causing this? I'm fairly sure it would only be either a fuel or ignition problem.

Thank you,
Jeremy

 

Check the EGR valve for carbon build up....also do the fuel injector cleaner and if that helps some then consider replacing the fuel metering block with a new upgraded version you can find them on '02 and newer 4.3L engines...or buy it new for approx. $300+ ...

Also make sure that the distributor vents are clear to stop moisture build up, and make sure that the camshaft sensor in the distributor is working correctly along with the ignition module...

 

again it was water in the gas for me the dry gas worked like a charm and dont go to that gas station anymore

 

So, I took it to a mechanic last week and he said the spider is just fine, and the fuel pressure is where it should be and holds well. They could not come up with anything on the computer, though.

They told me to come back again when it is acting up and see what the computer will say. Today I took it in again, and we drove it around town with the real-time scanner showing misfires in Cylinder 4. But after an hour or so of looking under the hood when we got back, they said the problem is gone and there's nothing left they can do at the moment. Since it only seems to act up in the first half hour, he thinks maybe a temp sensor isn't working right, and I'm leaving the truck there over night for a cold start again. Should expect a phone call around 9am tomorrow, hopefully with a solution!

I cleaned my EGR again this morning with a wire brush and a pipe cleaner, but when I started to drive this morning, the misses were terrible and the SES came back on again.

 

So today I get a call about 1:00pm saying cylinder 4 is misfiring and he thinks replacing my brand new spark plug will fix the problem. I told him it was missing before I put new spark plugs in. I replaced spark plugs that were less than two years old two weeks ago hoping to cure my misfire. None of the 6 plugs looked fouled or damaged then. Basically he thinks my Bosch Platinums are crap to begin with. Well if he replaces my plug and the misfire doesn't go away, I will not be happy if he charges me for something I was completely against.

Am I overreacting if it's standard practice for autoshops to think they can do anything they want to a vehicle and bill me for it even if I'm sure it won't fix it?

Or is it likely that Bosch products really are inferior and he's probably seen things like this before?

 

Check for debris inside of the distributor housing. I had a piece of an old rotor stuck in there and it would arc every once in awhile... huge pain in the *** that took me about a year to finally figure out. I must've spent close to a grand trying to fix the misfire.

 

OK, problem fixed, I think. So he did replace the spark plug, and we asked for the two-week-old one back, which we'll reinstall next weekend. Naturally, the problem didn't go away. So instead of letting them keep it overnight again, we took it home ourselves and took it to another shop out of town this morning. An hour later, the truck is running very smooth on the 20 mile drive home.

It turns out my cam was off by 14 degrees and they ground out the hole just a bit. So basically I spent several hundred dollars replacing things left and right, all for a $65 labor charge and one hour of waiting this morning to fix, which I felt was a very fair deal! It was some expensive trial and error, but at least I've got peace of mind with all the preventive maintenance over the last month. Now to fix my A/C and struts and I'll be set for the summer!

 

Something else is wrong if your timing was off by 14 degrees... The base timing cannot be changed on these engines without modifying the distributor clamp. So something else is out of whack that caused the timing to be off.

Either that or the computer timing control was not bypassed to check the base timing. This would lead me to believe that there is a sensor issue that is causing the timing to be advanced or retarded (you didn't specify) by 14 degrees. I'm not sure of the allowable limits to timing modification in the PCM, but I have to assume there is some kind of limit... By modifying the base timing, you could cause more issues.

At any point in time during the diagnosis of this vehicle, did anyone hook up a scan tool and watch the timing advance? the knock retard? the knock sensor active count?

And just to answer a previous question, I think that Bosch spark plugs & O2 sensors are one of the worst products of their kind for a GM vehicle.

 

Hate to bring up an old topic but i did a scan and it came back as random cylinder misfire. Im currently changing the plugs, I got 2 4 and 1 with no problem. For some reason (maybe im just not doing it right) but i cant get the boot off number 6, it looks like i would be able to easily swap plugs if i could only get the boot off. Ive twisted and pulled all of that. Also I read that #3 is problematic and that some people take the steering shaft apart etc. Im alil hesitant about doing that becuase i dont want to F things up big time. And I cant seen to find any info on number 5 but it looks a wee bit tricky too since its packed back in there any advice?Also when i scanned it said something about the o2 sensor in bank 1 being lean so i got a new o2 sensor and ill be putting that on promptly.

My car doesnt shake constantly it shakes weakly and randomly at a stop until it gets warmed up then it shakes all the time if this helps any.

I am in an auto tech class at the local technical college and whenwe pulled out plug 2 and 4 theywerent too bad but still not clean either. However when i pulled out plug 1 it was black and dirty as sin so my instructor saidtomorrow we are going to test my injectors by firing them individually and checking the fuel pressure. Any other suggestions on what i should check?