Blazer mis-fires when above fast idle

I sure hope someone can help me with this. I have a '95 Blazer, automatic, 4.3, CPI. It idles fairly well, but when you accelerate
it starts mis-firing, shuddering and back firing through the exhaust.
It does this on the road or not on the road. If you put a timing light
on any of the plug wires it will go out every time it mis-fires and
shudders. I have replaced the PCM, Crank position sensor, Ignition coil,
Ignition module, Coolant temp sensor, Spark plugs, Plug wires, Distributor
cap, Rotor, Distributor and Fuel regulator.

I didn't have this problem untill I replaced the distributor. I tried putting the old distributor back, but it didn't help. I replaced the distributor because I had very poor mileage (15 highway) and the timing was not advancing. My "mechanic" said the distributor was defective.

hmmmm,,,, the original problem was that the ignition was not advancing. How did the mechanic know it was the distributor?

My first guess, and I don't like guesses would have been to check the knock sensor.

Did he scan the engine with a scanner and review the data?

I will tell you one thing. Had a Blazer with a 4.3 vortec in our shop a while back but I can't seem to remember the year. Anyway, this too needed a distributor. We put one in, ran fine for a while, then another, ran fine for a while, and then another. When the third one went out on warranty we started to look into it. Here it turns out that the distributor was not being grounded properly. A little emory paper and it hasn't been back since. At least not for the distributor.

I would definately recommend a scanner to look at what the engine is doing and put the shotgun back on the rack.

JMHO, Good Luck!

I sure hope someone can help me with this. I have a '95 Blazer, automatic, 4.3, CPI. It idles fairly well, but when you accelerate
it starts mis-firing, shuddering and back firing through the exhaust.
It does this on the road or not on the road. If you put a timing light
on any of the plug wires it will go out every time it mis-fires and
shudders. I have replaced the PCM, Crank position sensor, Ignition coil,
Ignition module, Coolant temp sensor, Spark plugs, Plug wires, Distributor
cap, Rotor, Distributor and Fuel regulator.

I didn't have this problem untill I replaced the distributor. I tried putting the old distributor back, but it didn't help. I replaced the distributor because I had very poor mileage (15 highway) and the timing was not advancing. My "mechanic" said the distributor was defective.

You need to have your computer hooked up to a scanner while this happens so you can check the sensors.

Did you replace the fuel pressure regulator, or the whole injector?

Did you replace the fuel lines going to the main injector?

hmmmm,,,, the original problem was that the ignition was not advancing. How did the mechanic know it was the distributor?

My first guess, and I don't like guesses would have been to check the knock sensor.

Did he scan the engine with a scanner and review the data?

I will tell you one thing. Had a Blazer with a 4.3 vortec in our shop a while back but I can't seem to remember the year. Anyway, this too needed a distributor. We put one in, ran fine for a while, then another, ran fine for a while, and then another. When the third one went out on warranty we started to look into it. Here it turns out that the distributor was not being grounded properly. A little emory paper and it hasn't been back since. At least not for the distributor.

I would definately recommend a scanner to look at what the engine is doing and put the shotgun back on the rack.

JMHO, Good Luck!


He used a scanner to determin the distributor was bad. it is a plastic distributor so I guess it doesent need a ground, at lease we never found one.

We only replaced the fuel regulator because we could see it was leaking. Could the fuel system cause the spark in the plug wires stop?

Sounds like the distributor is a tooth off or perhaps 180* out of line.

Other than that, check you upper plenum for injector and fuel line washing.

We only replaced the fuel regulator because we could see it was leaking. Could the fuel system cause the spark in the plug wires stop?

You sure the cylinder is not getting spark?

We tried advancing and retarding the dist one tooth, but it ran even worse. The only sign of washing we found was where the regulator was leaking.

We had a timing light on it and when the engine mis-fired the light would not flash. Same on all wires..

We tried advancing and retarding the dist one tooth, but it ran even worse. The only sign of washing we found was where the regulator was leaking.

You sure the cylinder is not getting spark?

You sure the cylinder is not getting spark?

We had a timing light on it and when the engine mis-fired the light would not flash. Same on all wires..

You need to have this hooked up to a scanner and have the sensors monitored.

could have a bad cam sensor.

I agree about the scanner, but it doesn't have a cam sensor.

I know I am an old man of 50, but I have never seen a distributor made of plastic. At least not in a 4.3. Next, I know how to use an MT2500 and a Modis, both SnapOn, and I do not believe you can come to a definitive "Yes" to determine that the distributor is bad. You may find data that will steer you there but if I'm wrong, I humbly apologize.

As to the distributor not needing a ground, never saw that one either. Whether it be points or an ignition module, It still needs a reference to ground.

You have replaced a lot of parts and I'm sure you pocketbook can prove it but it might be time to take two steps back and take a smoke break or whatever.

1. What was the original problem or symtom that the mechanic diagnosed the distributor being bad?

2. I'm assuming here so bear with me. The mechanic said you needed a new distributor so you purchased one and R&R. Then you started having the misfire. I would reevaluate your installation.
A. Did you change the wires? If you did, are you sure that the firing order is correct?
B. Remove the cap and inspect VERY closely the reluctor to see that it is not cracked.
C. Check all the connections that plug into the distributor.

You need to look at what was done that created this problem since it appears that it wasn't there before you changed the distributor. If necessary, remove the spark plug from #1 cylinder and find top dead center. Remove the cap and look to see if the rotor is lining up with the #1 wire. If it's not, you need to take corrective action. It might be as simple as the wires are all one plug off around the distributor or it could be a tooth off but it has to be something of this nature since it occured after you installed the distributor.

Take a deep breath and review your work, Good Luck!

I agree about the scanner, but it doesn't have a cam sensor.

then why does my 1995 Blazer have one?

then why does my 1995 Blazer have one?

Not sure about that. Does your plug wires plug into the top or the side of your dist cap?

My mistake, I meant crank position sensor.

I know I am an old man of 50, but I have never seen a distributor made of plastic. At least not in a 4.3. Next, I know how to use an MT2500 and a Modis, both SnapOn, and I do not believe you can come to a definitive "Yes" to determine that the distributor is bad. You may find data that will steer you there but if I'm wrong, I humbly apologize.

As to the distributor not needing a ground, never saw that one either. Whether it be points or an ignition module, It still needs a reference to ground.

You have replaced a lot of parts and I'm sure you pocketbook can prove it but it might be time to take two steps back and take a smoke break or whatever.

1. What was the original problem or symtom that the mechanic diagnosed the distributor being bad?

2. I'm assuming here so bear with me. The mechanic said you needed a new distributor so you purchased one and R&R. Then you started having the misfire. I would reevaluate your installation.
A. Did you change the wires? If you did, are you sure that the firing order is correct?
B. Remove the cap and inspect VERY closely the reluctor to see that it is not cracked.
C. Check all the connections that plug into the distributor.

You need to look at what was done that created this problem since it appears that it wasn't there before you changed the distributor. If necessary, remove the spark plug from #1 cylinder and find top dead center. Remove the cap and look to see if the rotor is lining up with the #1 wire. If it's not, you need to take corrective action. It might be as simple as the wires are all one plug off around the distributor or it could be a tooth off but it has to be something of this nature since it occured after you installed the distributor.

Take a deep breath and review your work, Good Luck!

50 is not too old..I'm 54. Yes the dist is plastic. The factory dist was plastic. All we changed when the mis-fire started was the dist. I put the old one back, but it didn't help. If it has a ground it must be in the wiring somewhere. We thought we might have cracked the cap..so we replaced the cap and rotor..no joy there.

This needs to be hooked up to a computer scanner and have the sensors monitored.

You really need to stop the wild goose chase and stop throwing random parts at the truck.

Get it scanned and stop what you are doing.

Ok, I am really confused.

Your first post you stated " I didn't have this problem untill I replaced the distributor. I tried putting the old distributor back, but it didn't help."

You then stated in your last post, "All we changed when the mis-fire started was the dist."

These statements present a dichotomy. Which is it? The first statement implies the mis-fire occured AFTER the replacement of the distributor. Then, the second statement implies that the distributor was changed AFTER the mis-fire began. What came first, the mis-fire or the changing of the distributor? It can't be both.

Please clarify or at least answer the questions that I asked:
A. Did you check your firing order. You did remove the wires and you might have gotten them wrong, you wouldn't be the first.

B. With an ohmmeter, did you verify a ground at the module?

C, And last but not least, did you pull #1 Plug and check for it at top dead center with the rotor aligning properly with the #1 on the cap?

Of course these questions ASSUME that the mis-fire was AFTER you changed the distributor.

If the mis-fire was BEFORE the swapping out of the distributor than a scanning to see what is going on should be done.

Ok, I am really confused.

Your first post you stated " I didn't have this problem untill I replaced the distributor. I tried putting the old distributor back, but it didn't help."

You then stated in your last post, "All we changed when the mis-fire started was the dist."

These statements present a dichotomy. Which is it? The first statement implies the mis-fire occured AFTER the replacement of the distributor. Then, the second statement implies that the distributor was changed AFTER the mis-fire began. What came first, the mis-fire or the changing of the distributor? It can't be both.

Please clarify or at least answer the questions that I asked:
A. Did you check your firing order. You did remove the wires and you might have gotten them wrong, you wouldn't be the first.

B. With an ohmmeter, did you verify a ground at the module?

C, And last but not least, did you pull #1 Plug and check for it at top dead center with the rotor aligning properly with the #1 on the cap?

Of course these questions ASSUME that the mis-fire was AFTER you changed the distributor.

If the mis-fire was BEFORE the swapping out of the distributor than a scanning to see what is going on should be done.

The mis-fire started AFTER I replaced the distributor. I thought the distributor was defective so in reinstalled the old one, but it did not help. When the mis-fire started I had not changed anything else nor had I removed the plug wires from the cap. I did check to be sure the wires were on correct. I did bring #1 cylinder up to TDC and checked the position of the rotor. The ignition module is mounted on the coil bracket and I will check the ground. When I said "All we changed when the mis-fire started was the dist"..I should have said "All we had changed when the mis-fire started was the dist." I'm not "throwing random parts at the truck". All the parts I replaced could cause this type of problem except the fuel regulator and I could see it was leaking. I have been doing this for a while also. [email protected]

Ok, I apologize to the list but I can't seem to get this through my head.

I was at the jobber today getting parts for a '94 Grumman (GM Chassis) and while I was there I asked if they had a distributor for a '95 Blazer 4.3 W engine. They went and got one off the shelf. And guess what? It was not plastic. I asked if they had any that were plastic and they laughed at me. I told them why and they said that every one they had was cast. We checked a '91, a '93, a '95 and a '97.

Will SOMEBODY please give me a part number or something? I got to see this for myself. I have seen my fair share of plastic intakes but so far no distributors.

The distributors have a plastic top but a cast shaft and everything.

Bring your distributor to them and have them check it out.

Ok, I apologize to the list but I can't seem to get this through my head.

I was at the jobber today getting parts for a '94 Grumman (GM Chassis) and while I was there I asked if they had a distributor for a '95 Blazer 4.3 W engine. They went and got one off the shelf. And guess what? It was not plastic. I asked if they had any that were plastic and they laughed at me. I told them why and they said that every one they had was cast. We checked a '91, a '93, a '95 and a '97.

Will SOMEBODY please give me a part number or something? I got to see this for myself. I have seen my fair share of plastic intakes but so far no distributors.

Believe me, I wish the Blazer distributors were not plastic. That is the craziest thing GM has ever done. The shaft is cast, but the case is black plastic. Screws hold real good in plastic. The difference you may have found is in the engine code. Mine is "W" and I think the other is "N".
I also have a '97 blazer and it's distributor is plastic.

Not sure if this is the right thread to ask this question in, but it was the best one I found: First of all, when would you want to replace the distributor, rotor, and plug wires? I am looking for guidance (then possibly step by step instructions) for replacing these. Are they expensive and/or time consuming? Is it necessary at a certain interval? I'm planning on doing the plugs first, but I've found a good thread to help me with that. I've got a '97 LS 4.3 Vortec, 105,000 miles. Bought it at 84k, not sure when plugs and all were replaced. Any advice will help.. THANKS!

If you do the plugs, you do the cap and rotor as well.

Wires should be ok and will not need replacing.

Also, check the wires going from your coil to the distributor cap for corrosion.