99 blazer falls on it's face on medium acceleration

[skooterbum]

you guys just helped me through one problem. now i am working on another. i have a 99 blazer with a 4.3. 106,000 miles. recently had the distributor replaced by a local shop. last summer i pulled the catalytic converter and gutted it. replaced the fuel filter 10 months ago. replaced the plugs 10 months ago. do not remember what brand of plug i put in it. air filter replaced 6 months ago.

my problem is, with the car in park, if i try to rev the car up fast, it hesitates, bogs down, won't gain RPM's. if i back out of it and feather the gas pedal it will eventually gain in RPM's.

still in park, if i floor the gas pedal it pops out of the throttle body, and tries to gain speed but bogs down more than gaining speed.

when running down the road, if i try to pass a car with medium acceleration, it bogs down. i have to back out of the gas, then it starts to take off. if i give it to much gas it will bog down again. i have to keep feathering the gas to get it to accelerate.

under normal driving conditions it runs ok as long as i don't have to accelerate fast. it pulls my little motorcycle trailer just fine. i recently hauled a big load of furniture in my trailer 200 miles out, and an empty trailer 200 miles back with no problems. so it still has power. i just can't accelerate fast.

i am going to put this in the shop next Tuesday if i can't find the problem. i am hoping i can get some suggestions here of things to try out myself first. or get some suggestions of what the shop should be looking at to try to fix this thing.

any help or suggestions will be appreciated
thanks
Ron

[TCGrove]

I have a 99 Blazer too that once had the same problem. It was usually worse in the summer during hot weather. I would pull out in traffic, hit the gas, and the vehicle would just lose it breath for lack of a better term. I can't give you a direct answer on what fixed it because I've done all the things you did, plus a new fuel pump, new O2 sensors (which helped a lot), and I cleaned the MAF sensor (it had a lot of build up). Somewhere in that mix, the problem went away. If you gut the catalytic converter you should start getting a code because your fore and aft sensors are reading too closely.

[skooterbum]

hey TCGrove, thanks for your response. i think ,as you did, it might be time to replace my O2 sensors. if i remember correctly, they make O2 sensors that are meant to be put in place of the factory replacements, when the cat has been gutted. i wonder if i need to request that the repair shop does a check on the fuel system ??

[viggy58]

i've never heard of o2 sensors that work on a gutted cat. i assume you're throwing a check engine light without the cat? any particular reason for gutting it? i would imagine that not having a functioning cat will screw up back pressure on the motor, causing problems.

also you could have a bad cam/crank position sensor.

[TCGrove]

There are 3 O2 sensors. One is tucked up by the steering shaft, the other two are on each side of the catalytic converter. I only replaced the ones by the converter. I believe a 7/8" wrench will fit the things, but I ended up buying a very cheap ($5-7) socket at the parts store which was much easier. I soaked them with penetrating oil. I actually tested the ones I took out with my ohm meter and a propane torch. One of the two was bad.

[skooterbum]

when i decided to gut the cat, it was because of the car falling on it's face on acceleration. it made no noticeable difference on the performance of the car after i gutted it. i have never seen the check engine light come on, on this car. i am pretty sure it comes on when i start the car, but it goes out just like all the other lights on the dash do after start up.

viggy58, i bet you are right about the gutted cat causing problems with the performance of my car. although like i said, it made no noticeable difference to the performance after i gutted it. i hope the repair shop can tell me more when they check it out. there are sensors made to replace the factory ones for situations just like mine. i am pretty sure most auto parts stores carry them, and they are sold on ebay too, "i think"...

TCGrove, i bet i need to replace my sensors. where is the MAF sensor ?? i have never heard of that one.

viggy58 said my cam / crank position sensor might be bad. is that something that would normally show up when a shop is checking the car out because of performance issues ??

i am an old timer that was born and raised around the older cars. there were no o2 sensors, or catalytic converters, or cam / crank sensors. things were a lot easier back then.

i think i am going to replace my o2 sensors, and find, and clean my MAF sensor before taking it to the shop. not knowing the past repair history of the vehicle, and having 108,000 miles on it, i don't think i would be wasting my money.

[TCGrove]

The MAF (mass air flow) sensor is the little box just past your air filter going into engine. I'm no expert, but I think it measure the air flow via a reference wire and hot wire (or resistor). The difference in cooling due to the air flow measure the amount of air entering the engine and your fuel to air ratio is adjusted somehow based on this. The wire tends to get dirt built up on it that the air filter doesn't catch and it acts like an insulator which affects the flow calculation. If you unplug the sensor and pull the box out it has four screws holding it together. Be very careful though. You can't just use any cleaner. They make MAF cleaner you can get at the parts stores. I used alcohol and a swab to clean the little wires and MAF cleaner on the honeycomb looking stuff that keeps the air flow smooth. A new sensor is very expensive, so you don't want to damage it. Make sure you put it back in the same direction you took it out. Good luck...

[skooterbum]

thanks for the information TCGrove. i really appreciate it. that is something i can easily do. i hate to put my car in the shop, but the older i get the less i can do.

i checked into the o2 sensors that are meant to replace factory sensors when the exhaust has been altered. they are called o2 sensor eliminators, and o2 sensor simulators. i think i will be finding out how well they work in the near future.

[skooterbum]

hey TCGrove, you was right on the money again !!! i ended up putting my car in the shop and let them find and fix the lack of acceleration problem. they said they checked everything out, and the MAF unit was bad. they replaced it and it [so far] is running much better.
thanks for the help !!!
ron