Blazer mis-fires when above fast idle

[chuckie4373-3]

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.

[Mikado14]

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!

[BlazerLT]

Originally Posted by chuckie4373-3

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?

[chuckie4373-3]

Originally Posted by Mikado14

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.

[chuckie4373-3]

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?

[BlazerLT]

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.

[BlazerLT]

Originally Posted by chuckie4373-3

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?

[chuckie4373-3]

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.

[chuckie4373-3]

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

[BlazerLT]

Originally Posted by chuckie4373-3

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?

[chuckie4373-3]

Originally Posted by BlazerLT

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..

[BlazerLT]

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

could have a bad cam sensor.

[chuckie4373-3]

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

[Mikado14]

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!

[BlazerLT]

Originally Posted by chuckie4373-3

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

then why does my 1995 Blazer have one?