Hello I have the 4.3 w code in my 94 jimmy and I just replaced the cpi and nut kit.When the engine is cold it runs perfect it is smooth and idles great.When it warms up it starts surging and running rough.It idles rough and sometimes almost stalls.When you get out of it,it also has a weird smell.its not gas I just cant describe it though.It might be burning converter or something exhaust related not sure.does anyone have any ideas on this .. thanks

Ok, let's go down the checklist...

1.) Have you replaced the cap & Rotor Lately?
2.) Have you replaced the plugs?
3.) Are you getting any check engine lights?
4.) Does it smell like rotton eggs?
5.) Replaced the fuel filter lately?
6.) Does the engine run a little hot?
7.) Have you removed and cleaned the EGR lately?

Ok, let's go down the checklist...

1.) Have you replaced the cap & Rotor Lately?
2.) Have you replaced the plugs?
3.) Are you getting any check engine lights?
4.) Does it smell like rotton eggs?
5.) Replaced the fuel filter lately?
6.) Does the engine run a little hot?
7.) Have you removed and cleaned the EGR lately?
BlazerLt I will answer your questions down the list.
1)I have replacedthe cap and rotor.When the truck first started running bad I thought it needed a tune up so I replaced the cap and rotor.
2)I replaced the plugs just yesterday because I was told when you have a cpi or nut kit leak it can foul the plugs so I replaced them.
3)The ses light did come on when driving and I havent got a chance to get to autozone to check it yet.I had a little key to check the code with but lost it.I am going to do this tomorrow I hope.
4)The smell might pass for rotten eggs its a weird smell not like gas.
5)THe engine does seem to get slightly hot.I noticed it getting alittle hotter than usual when I started getting all these problems.Its not overheating and the temp doesnt get in the danger zone but it does seem to get alittle hotter lately.
7)I cleaned the egr when I had the top intake off.It moves freely and there wasnt any big carbon build up.I cleaned everthing good.
thanks for any help you can offer I appreciate it very much.I am starting to feel like im throwing money at this thing and not gaining any ground.. thanks Joe

Sounds like your leaking CPI unit ruined your cat.

The hotter operating temperatures and weird smell usually are a sign.

Also, have you had the timing set lately with the timing wire disconnected from the PCM?

Sounds like your leaking CPI unit ruined your cat.

The hotter operating temperatures and weird smell usually are a sign.

Also, have you had the timing set lately with the timing wire disconnected from the PCM?

Thanks for your info on this Im getting alittle stumped.would the cat cause the truck to run rough and surge when it is bad.And also would it run fine when cold.I havent done anything with the timing as of yet but I will double check it just to make sure.I have heard of the o2 sensor being a problem something like this but Im just not sure what is your take on this..Thanks again for your information it is helping a ton.I started off totally lost and intimidated with working on this thing and at least now I have a wealth of tried testing on these problems...
thanks again Joe

A plugged cat can cause this because it will usually screw with the MAP sensor readings.

When an engine is cold, the engine runs in open loop and runs off the computers set values for all the sensors.

After 2 minutes or after a certain operating temperature is reached, the engine will go into closed loop whcich means it will go to live sensor data coming from all the sensors to calibrate the timing and the fuel/air mixture.

Also, a plugged cat will get worse when it gets warmed up. This is what happened to mine.

First I would check the timing without the timing advance wire attached to the PCM. It is a beige and brown wire running under the carpet under the glove compartment. You disconnect it, set the timing to zero using a timing gun and then reconnect it. An overly advanced timing condition could be set because of the engine running so rich due to the poor CPI unit. In essence you will be setting the setting back to factory to reflect your newly replaced fuel system.

A plugged cat can cause this because it will usually screw with the MAP sensor readings.

When an engine is cold, the engine runs in open loop and runs off the computers set values for all the sensors.

After 2 minutes or after a certain operating temperature is reached, the engine will go into closed loop whcich means it will go to live sensor data coming from all the sensors to calibrate the timing and the fuel/air mixture.

Also, a plugged cat will get worse when it gets warmed up. This is what happened to mine.

First I would check the timing without the timing advance wire attached to the PCM. It is a beige and brown wire running under the carpet under the glove compartment. You disconnect it, set the timing to zero using a timing gun and then reconnect it. An overly advanced timing condition could be set because of the engine running so rich due to the poor CPI unit. In essence you will be setting the setting back to factory to reflect your newly replaced fuel system.
thank your for the info.I will be working on this off and on for this week so I will keep the forum posted of what I find.This might possibly help someone else with the same problems...thanks again joe

no problem, let me know

Thanks for your info on this Im getting alittle stumped.would the cat cause the truck to run rough and surge when it is bad.And also would it run fine when cold.I havent done anything with the timing as of yet but I will double check it just to make sure.I have heard of the o2 sensor being a problem something like this but Im just not sure what is your take on this..Thanks again for your information it is helping a ton.I started off totally lost and intimidated with working on this thing and at least now I have a wealth of tried testing on these problems...
thanks again Joe

What LT said is true.

However, one other thing is the O2 sensor. Depending on how long you drove the truck in that condition (rich) you may have also damaged your sensor. The openings in the sensor accumulate carbon as well as the inside. If your cat is plugged or restricted, as it sounds, you may want to consider the sensor as well. At least it is only one and not several.

What LT said is true.

However, one other thing is the O2 sensor. Depending on how long you drove the truck in that condition (rich) you may have also damaged your sensor. The openings in the sensor accumulate carbon as well as the inside. If your cat is plugged or restricted, as it sounds, you may want to consider the sensor as well. At least it is only one and not several.
thanks for your info also..I actually going to replace the o2 sensor also when I do the cat..I called today to check on pricing of the cat and sensor so I will go ahead and replace both of them while im doing it.I appreciate all the input on this problem it helps alot.
thanks again Joe

What did they give you on the pricing?

What LT said is true.

However, one other thing is the O2 sensor. Depending on how long you drove the truck in that condition (rich) you may have also damaged your sensor. The openings in the sensor accumulate carbon as well as the inside. If your cat is plugged or restricted, as it sounds, you may want to consider the sensor as well. At least it is only one and not several.

Wouldn't he get a code for that and a check engine light?

Wouldn't he get a code for that and a check engine light?

Yes it would, just as he said it did in his second post.

What did they give you on the pricing?
Sorry this is alittle late..the pricing on the sensor is 48.00 and the cat is 56.00 for a fit all and 118.00 for a same as I have catalytic converter.I might go with the fit all since I do some of my own pipe work..I do alot of fabrication out of my shop and It wouldnt be any problem to fit one if its at least close to the old one... take care

If you are going to be replacing the cat, replace it with a universal Carsound Magnaflow.

It is a lot smaller and flows a lot better and man does it make the exhaust sound nice.

The stock cat acts like a resonator and the small new universal does not and will sound a lot better.

If none of that works, try a new coil. When the old coke can coils were going bad, they would start making the engine run bad or stall. Correct me if these new coils don't do that.