99 suburban mid rpm breakup...

[warren33]

I have a 5.7 that has had PO420 & PO430 codes for a long time. I have had an unusual problem that would occur once in a while when ambient temps were warm to hot. I would get a mid to high rpm acceleration breakup where I could not increase or maintain speed, let it cool, it would start and you could continue. This occurred 3 or 4 times in 6 months. Now it is constant. After warm up when at temperature, when accelerating, it bogs down, pops and spits, won't accelerate. I attached a fuel pressure gauge and have 60 psi when you turn the key-engine off. After start up which is usually good, but every once in a while it will crank and crank, but if you cycle the key one time it starts right up. It always starts and runs well at idle cold or hot. After start, there is 53 psi idling. Accelerate it goes to 60 psi, let off, 50 psi and when it reachs idle, goes right back to 53 psi. Now for what I have done, I replaced the y-pipe with the two cats in it, along with the 2 upstream O2 sensors, and both down stream O2 sensors. I installed new doughnut seals at the manifold and the rear gasket. This got rid of those pesky PO420, and PO430, and the recient PO151 codes (forgot that one). Still have the bogging down issue. I replaced the ignition coil and the distributor module, problem still exists. The cap, rotor, wires, and plugs are not that old. I checked the wires in the dark and see no arking as well as felt each one and recieved no jolts. I wanted to pull a plug to check for wear and the gap as they may have been stressed from the O2 problem. I was wondering if anyone else has experienced this issue and what might be suspect. One of the two cats was empty so I also wonder if the muffler could be plugged, if so, how do I check that as I could not get it out without a lift. Thanks for reading.

[warren33]

I also forgot to mention I replaced the air and fuel filters.

[MT-2500]

Originally Posted by warren33

I have a 5.7 that has had PO420 & PO430 codes for a long time. I have had an unusual problem that would occur once in a while when ambient temps were warm to hot. I would get a mid to high rpm acceleration breakup where I could not increase or maintain speed, let it cool, it would start and you could continue. This occurred 3 or 4 times in 6 months. Now it is constant. After warm up when at temperature, when accelerating, it bogs down, pops and spits, won't accelerate. I attached a fuel pressure gauge and have 60 psi when you turn the key-engine off. After start up which is usually good, but every once in a while it will crank and crank, but if you cycle the key one time it starts right up. It always starts and runs well at idle cold or hot. After start, there is 53 psi idling. Accelerate it goes to 60 psi, let off, 50 psi and when it reachs idle, goes right back to 53 psi. Now for what I have done, I replaced the y-pipe with the two cats in it, along with the 2 upstream O2 sensors, and both down stream O2 sensors. I installed new doughnut seals at the manifold and the rear gasket. This got rid of those pesky PO420, and PO430, and the recient PO151 codes (forgot that one). Still have the bogging down issue. I replaced the ignition coil and the distributor module, problem still exists. The cap, rotor, wires, and plugs are not that old. I checked the wires in the dark and see no arking as well as felt each one and recieved no jolts. I wanted to pull a plug to check for wear and the gap as they may have been stressed from the O2 problem. I was wondering if anyone else has experienced this issue and what might be suspect. One of the two cats was empty so I also wonder if the muffler could be plugged, if so, how do I check that as I could not get it out without a lift. Thanks for reading.

Fuel pressure is low .
You need to get it up to specs.

Get a fuel pressure gage on it and see what it is doing when it bogs down.

To check for restricted exhaust check engine vacuumn at idle and at 2K rpm.
If lower at 2K RPM your exhaust is restricted.
Ifr missing/poping/spiting at high speeds go over plugs and wires and cap and rotor and check for good hot blue spark.
AND USE GODD AC DELCO PARTS.

[j cAT]

Originally Posted by warren33

I also forgot to mention I replaced the air and fuel filters.

need to measure plug wire resistance..if open or too high these must go.

plugs need replacing when you have had much work done in the ignition components plugs take a great amount of damage.

use the ac delco plugs.

p0151 code swap upstream O2 sensors see if code changes.

could be low fuel pressures ....could be the muffer is plugged with old converter guts.....could be the distributor bearing is shot....or the distributor cam gear is getting very worn ......or a mix of any of these items...time to start looking testing...post back how it works out...

[MT-2500]

On private E mail no sure My PC got it answered.
But it is best to keep most stuff in the open forum so everyone can see and read and help with your problem.

Factory specs on fuel pressure is 60/66 lbs.

You should see full 66 cold start and 63-65 running on road.
Full pressure with return line pluged should hit 95-105 lbs.

Your fuel pressure is reading 10 or more lbs low.
Low fuel pressure or low fuel volumn can cause misfire under load.
The GM V6 & V8 need the pressure up to specs to run right.

[warren33]

MT2500 you were right on the money. The very first time it acted up, my immediate thought was oh no...not the fuel pump again. Anyway, I never had any fuel pump, let alone all the ones I put in this vehicle fail and still start and run the vehicle...never. Everyone else felt the fuel pressure was sufficient but you. Luckily this pump was still warrantable by one month. So I ordered an A/C fuel pump and paid the difference. Problems solved...and along with the other repairs I did up and to this point, it runs the best it has in a long time. Thank you again.

[MT-2500]

Originally Posted by warren33

MT2500 you were right on the money. The very first time it acted up, my immediate thought was oh no...not the fuel pump again. Anyway, I never had any fuel pump, let alone all the ones I put in this vehicle fail and still start and run the vehicle...never. Everyone else felt the fuel pressure was sufficient but you. Luckily this pump was still warrantable by one month. So I ordered an A/C fuel pump and paid the difference. Problems solved...and along with the other repairs I did up and to this point, it runs the best it has in a long time. Thank you again.

You are welcome and thanks for posting back how it went and the fix.
The Ac Delco/Delphi fuel pump is the way to go.
Good luck with it.