99 blazer wont chokes when hot

i have a 99 blazer 4.3 vin W that i am having serious problems with. when the truck is cold it runs great. but after driving for an hour or so it loses all power and will not accelerate when i give it gas. if i keep the throttle at a certain position it will slowly accelerate if im not on an upgrade. if i push it any further it chokes. i had this same problem 5 months ago and replaced the cat, muffler and tailpipe. it took 2 days afterwards before it would run right but i thought that was the system resetting itself. now its 5 months later and i have this problem all over again! when i am coming to a stop the fuel pump squeals very loud but once i stop it quiets down. the truck runs fine at idle but if i try to accelerate it chokes. is it possible the cat is plugged again already? or is this a fuel pump issue? please help!

The fuel pump should not squeal.
It may be failing, which would cause poor acceleration.
You would need to test the pressure at the fuel rail, or try another pump to find out.

It may also be an ignition problem. Thermal expansion can cause things to run well when cold, but fail when hot.

i only notice this squealing when slowing down for a ligh or stop sign. and as im slowing down, the rpms drop below 500 and it wants to stall. sometimes the engine dies and i have to try for quite sometime to get it to start again. if it doesnt stall. the fuel pump becomes quiet again and everything is fine other than no power when i try to go again. it seems to me the fuel pump would only squeal that loud if it is working harder than it should.

like moppie says, the only way to check is to put a gauge on,& drive it until it acts up

i will see if i can get a tester after work tomorrow.

i would also like to add that this happens instantaneously. i dont gradually lose power, it can be running fine at 55 and then it instantly drops all power.

pick up a spark tester if you can. there pretty cheap $5 or so & check for spark when it
stalls out.

i picked up a fuel pressure tester today and hooked it up. pressure readings are as follows...

ignition on no start-60 psi
engine running-54psi
running while driving-54psi
when problem occurs-54psi

i didnt even have to go anywhere today just left it running in the yard and the problem showed itself.

im really starting to think the cat is plugged again. but is that possible after just 5 months?

is the 54 psi to low? it is idling fine and was running fine when i went to pick up the tester.

the mechanic told me to get a fuel filter. maybe i am over-thinking this but if the filter was plugged wouldnt i have this problem all the time? even when cold?

i picked up a fuel pressure tester today and hooked it up. pressure readings are as follows...

ignition on no start-60 psi
engine running-54psi
running while driving-54psi
when problem occurs-54psi

i didnt even have to go anywhere today just left it running in the yard and the problem showed itself.

im really starting to think the cat is plugged again. but is that possible after just 5 months?

is the 54 psi to low? it is idling fine and was running fine when i went to pick up the tester.

the mechanic told me to get a fuel filter. maybe i am over-thinking this but if the filter was plugged wouldnt i have this problem all the time? even when cold?

it dose sound like you my have got a bad cat. but like he said check for spark when it acts up and look down at cat and see if it's pluged enough to get red hot if it don't it still could be half pluged. another thing the fuel pump could be getting hot.

good luck...

i havent checked spark yet but i did call advance and check the warranty on the cat. its 5 years if defective. the manager there told me he would check with walker to see if "plugged" is covered in the warranty but he believes it is not.! that tells me to go with the magnaflow next time with a 90 day warranty for $40 cheaper!. apparantly my truck is the reason it would plug up in a 5 month period. i think ill just knock it out if its not covered. if in fact this is the problem. bad spark would make sense if it wasnt idling at all or running rough all the time but if i feather the the throttle the rpms will rise and it runs smooth all the way up. its only if i stomp it to the floor that it chokes.

i picked up a fuel pressure tester today and hooked it up. pressure readings are as follows...

ignition on no start-60 psi
engine running-54psi
running while driving-54psi
when problem occurs-54psi

i didnt even have to go anywhere today just left it running in the yard and the problem showed itself.

im really starting to think the cat is plugged again. but is that possible after just 5 months?

is the 54 psi to low? it is idling fine and was running fine when i went to pick up the tester.

the mechanic told me to get a fuel filter. maybe i am over-thinking this but if the filter was plugged wouldnt i have this problem all the time? even when cold?

were you looking at the pressure when it was stalling & it stayed at 54 psi
or was it already stalled out??
60 psi koeo is the minimum pressure 60-66(not saying its the problem just low) does it hold the pressure when key is off??

it doesnt stall out unless i stomp the gas. it was at 54 when i decided to go for a drive but couldnt get out of the driveway because it was choking when i gave it gas. so i sat there and feathered the throttle and it stayed at 54. when i stomped the throttle it remained at 54. so it doesnt change when its choking or if it runs good. again it doesnt stall out unless i stomp on it. and i usually let off before it dies and the rpms drop to 500 and then level out at 600.

just to add... when i shut the engine off the pressure slowly rose to 60psi and held there for a few minutes but it is now at 25 after sitting 20 minutes

i havent checked spark yet but i did call advance and check the warranty on the cat. its 5 years if defective. the manager there told me he would check with walker to see if "plugged" is covered in the warranty but he believes it is not.! that tells me to go with the magnaflow next time with a 90 day warranty for $40 cheaper!. apparantly my truck is the reason it would plug up in a 5 month period. i think ill just knock it out if its not covered. if in fact this is the problem. bad spark would make sense if it wasnt idling at all or running rough all the time but if i feather the the throttle the rpms will rise and it runs smooth all the way up. its only if i stomp it to the floor that it chokes.

that's what i would do on the magnaflow also does that have a dist or coil pack? it's probably the HEI so that means a cap on it. also could be out of time since it runs better in the cold than the hot or the other way around.

it has a distributor which oddly enough when i bought the truck it had a broken ear so the cap is held on with cable ties. i highly doubt this could be the cause of my problem since it ran fine for almost a year before the cat plugged the first time and until now has been running fine for 5 months since i replaced the cat

can you get vacuum gauge maybe from a loan a tool at parts house?
if you are thinking clogged cat,this will tell you if the vacuum is a problem
ei, reads 17 then slowly falls to 0 & back up (at idle of course)
alot easier than droping the exhaust

can you give me some instructions on how to do this? where do i connect the vacuum guage? will this tell me if the cat is plugged?

can you give me some instructions on how to do this? where do i connect the vacuum guage? will this tell me if the cat is plugged?

this is a a good explination of how to

sorry it won't allow copy/paste.. pm me your e-address i'll e-mail to you

e-mail sent

it has a distributor which oddly enough when i bought the truck it had a broken ear so the cap is held on with cable ties.........



It is not a plugged cat.
If it is, you have Major problems with running rich, or leaded fuel, etc.

I would put money on it being the distributor, or similar.

Replace the cap, rotor, coil pack, plugs and leads.

ok i couldnt find a vacuum tester but i changed the fuel filter and nothing changed.

i have noticed that there is a serious amount of corrosion on the positive battery terminal. and on the tray as well. could this be the cause of the problem?

ok i couldnt find a vacuum tester but i changed the fuel filter and nothing changed.

i have noticed that there is a serious amount of corrosion on the positive battery terminal. and on the tray as well. could this be the cause of the problem?



That wouldn't help.

Sounds like this car has a whole raft of things wrong with it.
You may find your problems are caused by a combination of things.

Replace the dizzy cap and clean up the batter terminals.
You can put some petroleum jelly on the positive terminal to stop it oxidizing.

ok i cleaned the terms and i also took the ignition control module off the heat sink where it is mounted and left it hanging. took it for a drive and this made a considerable difference. still not the power i should have but i was able to cruise at 55 unlike before.

Do you smell gas when this happens? Sounds like a leak down problem, You should not lose that much pressure when the key is off. Culprits could be a bad spider or fuel pump.

Is your ICM too hot to touch after a few minutes? It could be failing hot.

no fuel smell ever. i got an icm from a junkyard today. seems ok so far. i still dont have the power i normally have but its not choking like it was. i do have an intermittent SES light now but its an hour drive to the closest autozone to have it read.

ok still having the same problem but updating...i have replaced the distributor, icm, cap, rotor and fuel filter. still nothing has changed. i have now noticed that the oil pressure drops to around 20 at idle when this problem occurs. when its running ok the oil pressure is just under 50 and then when it decides to crap out the pressure drops to just above 20 at idle. any ideas?