Misfire On 3 And 6

SS-ZR2 · January 20, 2008

2000 S10 ZR2 4.3 W

The plastic dist cap screw tab on the distributor base broke. I replaced the cap and rotor and held the cap on with a c clamp(lightly) temporarely and everything ran fine. I replaced the distributor, put on the new cap and rotor and had a bad miss. I replaced the wires and plugs and still had a bad miss. Checked the codes, misfire on 3 and 6. Cleared all the codes, but again got a misfire on 3 and 6. Checked everything inside and out, all read perfect except the misfire on 3 and 6. Put everything back original, still same misfire. Put all new back in, still misfiring on 3 and 6, everything else perfect. Everything double and triple checked. All new stock GM parts used.

SS-ZR2 · February 7, 2008

Still No replies?

I replace the crank position sensor, no luck, still missing.

SS-ZR2 · February 16, 2008

I pulled the plugs on 3 and 6 and they're dry. I assume the injectors aren't working. How can I check if the injectors are getting power before taking everything apart?

L29er · February 16, 2008

this is a farmer way to do it, get some 194 bulbs (little guys) then take em and pry the metal wires so it looks like a pulled tooth(:. unplug suspect injector hold wires to connections of pigtail for injector, have somebody start your truck and see if the bulb flashes, i have a noide test light set and thats basically what they are.

minibike132 · February 16, 2008

If it was ok before you replaced the distributor why would you assume fuel? I would assume something is not quite right with the distributor install if the same situation happened in my bay. Now some times bad coincidences happen where you could get unlucky and get a different problem after fixing the first one but I would go over the install with a fine toothed comb to make sure everything is ok. You said you installed the original parts and still had the 3,6 miss. It's probably not possible you crossed the 3,6 wires but it is possible to get 3 and 6 crossed inside the cap if the cap is bad.

minibike132 · February 16, 2008

this is a farmer way to do it, get some 194 bulbs (little guys) then take em and pry the metal wires so it looks like a pulled tooth(:. unplug suspect injector hold wires to connections of pigtail for injector, have somebody start your truck and see if the bulb flashes, i have a noide test light set and thats basically what they are.

do not do this a noid light is the correct tool it is a high impedence led not a light bulb. A bulb CAN dammage the pcm circuit. Before you start arguing that you've done it before notice i capped can. It may not happen but it can and I wouldn't experiment with a 300 dollar pcm instead of buying a 10 dollar tool.

minibike132 · February 16, 2008

Besides that the 4.3 W motor has a central sfi system and he wouldn't know which wires to go to.

L29er · February 16, 2008

yeah, thats why i should keep my mouth shut! lesson learned, mouth zipped, er hands tied, whatever! sorry i know my place,):

minibike132 · February 16, 2008

I'm not scolding just educating

L29er · February 17, 2008

thanks, but i just need to learn to "leave it alone" sometimes, i like being helpfull, but i should leave it to someone who knows more, i haven`t pulled a wrench ona car in 3 years, so things change, i`m gonna keep my self to questions instead of answers!!

minibike132 · February 17, 2008

I don't really know what to tell you to check if your sure that everything is installed correctly and you got the right and known good parts. The problem is what we would do as gm techs you probably wouldn't have access to the tools we would be using as they are quite expensive. If you want to buy a noid light I can tell you how to check if the pcm is telling that injector to fire and if there is power there but thats skipping a few steps. We would watch for fuel pressure drops while commanding each injector on. This requires about 6 grand worth of tools. If you have a fuel pressure gauge you could install and check for a stuck open one but you said the plugs were dry.

SS-ZR2 · February 26, 2008

Thanks for the feedback. I'm interested to know the noid light test procedure. I have most tools, including the noid light, just don't have access to the diagnostic instructions. I'm not against replacing things, but I would like to be able to diagnose too, before the whole engine is new.

Assuming everything has been checked and re checked several times and all replacement parts ar GM, whats next?

The miss is always 3 and 6, no matter what. I put everything back and forth in every configuration, new, old, new with old, and still misses on only 3 and 6, everything else reads perfect. I pulled the 3 and 6 plugs after running briefly and they're dry. This has to be a coincedence because before changing the distributor it ran fine, even after the new cap and rotor. It only began to miss after removing and replacing the distributor because the screw tab broke, and missed ever since.

Thanks

SS-ZR2 · February 27, 2008

Noid light test good at all injectors, spark test good at all plugs. 3 and 6 plugs are dry. 3 and 6 injectors must not be shooting. Thats all thats left. I read somewhere that you could replace this injector system with a later version, an upgrade. If I replace the injectors, which way is best to go?

Thanks

minibike132 · February 27, 2008

Sorry I didn't get back to you I've been busy busy but it looks like you figured it out anyway. I'm going to get a little winded here for educational puropses if you already know all this just ignore me, the explananation could help someone else searching this problem. You have a CSFI system, all of the fuel is delivered to the injector body that houses the injectors. When the injector triggers the fuel is delivered from the injector to the cylinder through a tube with a poppet ball valve at the end. The injectors don't really get clogged in this system the poppet does. I have alot of success cleaning these systems but I wouldn't go to pep boys or the like for cleaning on this system especially. There is a special procedure for cleaning these poppets that involves using 150 psi of compressed nitrogen to the injector body with the rest of the fuel system disconnected and shut off. Then we use a special tool to activate each one at a time till the desired pressure drop is noted. Then we hook up the normal cleaning cylinder and run a couple of canisters with cleaner through at 75 psi. The procedure is involved and takes a couple hours usually so it can cost you. I would say when done correctly this works about 90% of the time (maybe more thats conservative). If it works you save alot of part money if not you just wasted that time and money but for my money it's a good gamble.

If you just want to skip all that there is an update to change from CSFI to MFI. I don't have parts pricing access here so I can't tell you how much the parts are. The difference in the system is that instead of the injector being at the top in the injector body then delivering the fuel to the cylinder through the tube, there is fuel delivered by tubes to each injector that is actually at the cylinder, voiding out the poppets. Eventually these clog too but it's not as big a deal to clean them and they do go quite a few more miles before becoming a problem. I have never noticed any difference in performance other than just the fact that the MFI doesn't clog as fast (just incase that is a question for anyone).

If you are going to replace the injector body I would just go whole hog and do the update. It's been quite a while since the cleaning didn't work for me so I can't even remember off the top of my head if you can replace just one tube from a CSFI. If one tube is an option it would be a much cheaper one than the conversion. If tubes are not replaceable or available and the whole injector body is needed check the pricing on both. With the updated parts there are a few things you need that you do not need to just replace the original. There is a different bracket and seal kit. If memory serves they are not that much. If you are replacing just check on the parts prices of the CSFI and the MFI and make your decision from there. Also while your getting your parts don't forget to get a new upper intake gasket and throttle body gasket.

There is a bulliten explaining cleaning and replacement procedures and the part numbers for the MFI conversion kit if you can find it or someone wants to send it to you (I don't do that anymore,sorry) the bulliten is 00-06-04-003B doc#1234172. Also if you live in California and have a vehicle registered there that was made with the California emissions option there is a special policy to cover this for 10 years or 200,000 miles in this case ignore all this, the fix is free just go to the dealer and let them handle it, the policy # is 99066G doc# 1400638. I hope I've helped and answered all your questions.