98 Sonoma Multiple cylinder misfire

[nate2424]

I recieved this code on my 98 sonoma, it has 97,000 miles, and is in good condition. I have done the standard tune up to correct this, that being plugs, wires, cap, rotor, pick-up sensor, and I still have the code, and a really rough running truck. Runs like the wires are crossed. (they are not, thats just to give you an idea of how hard the motor mounts are working) The number escapes me right now, but I will post the exact code soon. I have read on another forum that it could be the crank position sensor, and I am asking if anyone can show me an exploded parts view to locate this. any pictures would be helpful.

Thank you.

Nate

[95MustangGTC]

I'd say its the crank position sensor.

[envoyxuv]

Is this the 4.3 engine? Have you performed a compression check? leakdown check? Injector balance test? These are all steps of diagnosing the concern.

[nate2424]

The code it is throwing is a "PO300, Random/multiple cylinder misfire".
Well I have now replaced the Crank positioning sensor, and that was not it.

I have another tip that it is the "TPI" sensor. I am not fapiliar with this part, but aparently it is on the distributor. The distributor needs to be removed and the part is actually pressed on. not expensive im told, just tedious in marking the distributor before its pulled, and getting it back in in the proper position.

I hear you on the compression check, I have been suggested on that, but what is a leakdown check, or how do you perform an injector balence check?

[nate2424]

It wasn't the Crank positioning sensor.

[envoyxuv]

You haven't stated whether this is the 4.3 liter V6 or the 2.2 liter 4 cylinder.

Leakdown test is used if you find a problem with the compression check. You need to identify what the problem is: is it a mechanical issue (valvetrain, pistons,etc) or is it electrical?

If you do a compression test and all of the cylinders come up with good compression, you know it's not a problem mechanically. Ideally, you need a good scan tool that's capable of displaying the misfire counters to see which cylinders are actually misfiring.

You can also use a pair of non conductive (plastic) pliers or rubber tipped spark plug wire pliers to remove plug wires one at a time from each spark plug while the engine is running. This will do two things for you: verify that you have spark- you will see it and hear it snapping as soon as the plug wire is disconnected from the spark plug (or distributor, whichever is easier). It will also help find which cylinder may be misfiring- if you disconnect a plug wire from a spark plug and have no engine rpm drop, that means the cylinder isn't doing it's job. The engine should run slightly rougher than normal with a spark plug wire disconnected from any given cylinder.

[rhandwor]

If you recently pulled the intake you could have hooked up the injectors wrong. This will make you think it was the plugs. Spray a little carb cleaner around the injectors a bad o-ring will cause a very rough idle.

[nate2424]

Well I broke down and stopped checking electrical. I took everyones advice and did a cylinder pressure check, 0% on #6 and 60% on cylinder #4. So I took the valve cover off and found a bent lifter rod on #6. does anyone have any idea what would have caused this?? again the truck was being driven when the failure occured, and I am not privey to any issues leading up to this. I am going to put a new rod in and see if it rides fine on the cam, but still don't know why it happened in the first place.

Nate

[blactracsonoma]

hello, i have read your thread, and I have a very very similar condition! I have the thread right above this one, titled; spark but no start.
Im sorry i dont have anything to contribute to for your sake, but if you could tell me how you tested the cam or crank sensor. Also, I have perfect spark, and when i spray starter fluid into the throtle body it wont even cough a little bit. This leads me to think its a timeing issue cus if it has spark, and fuel (starter fluid) it SHOULD start on that. But since it doesnt it seems like a timeing issue. How exactly did you find this bent valve, just from the compression test?
- since you are wondering how that might have happened, the only way i know of how something like that can happen is the engine timeing being off!
Which is not good. Since your engine is an interferance engine, that means the piston and valves occupy the same space, just at different times when the timeing is correct. So that would mean it your timeing would have to be off. Also check the timeing belt or chain, (whatever you have) of your engine and reset it. Since I think it is your timeing, other internal damage may have occured. It would be helpful to know exactly what/how you were driving or doing with the truck when it died on you. Did you hear any strange noise? Let me know please, sounds like you and i have the same problem, well very very similar.