97 Suburban 5.7L Issues

I bought it a year ago with 220,000 miles. It had a new motor with only 3000 miles on it. (I verified this). But it has never ran correctly. Here is how it runs... It is gutless climbing any kind of hill. If I floor it, it will only rev to about 3500 and will bog down and stutter even under no load. If I am going down the highway and floor it, it does the same and it is like the transmission kicks into neutral, I actually lose speed. Idling at stoplights it seems fine but when I get on it to go it stutters and stammers almost to the point of dying, then after it gets rolling it will clean itself up. If I am easy on it, it gets around fine but has no real power. The only code I have ever gotten from it has been for low voltage on O2 sensor S1-B1. When I had it checked out the mechanic said the cat was plugged. I changed using a Flowmaster premade pipe and cats, but I did not change the o2 sensors or muffler. It did not change how it ran. I took it back and he said the same thing. I told him I changed it but he insisted it had to much back pressure. I asked if the O2 sensors could be causing it and he said he didn't think that they would have that big of an effect on it the way it ran. So I changed the exhaust as well to a Flowmaster thinking maybe it was plugged. Again no change.

Can bad O2 sensor readings make it run this bad? Can it cause the Cats to plug again within 5000 miles?

When I checked the spark plugs they looked like it was running lean, not rich. To me it seemed like timing but I don't have a scanner good enough to read or set it. Fuel pressure checked out at 60psi so I don't thinks its that.

Got any thoughts?



PS Thanks for all you guys have contributed. I have been reading post for the last 3 hours. Bad news is oit looks like it could be anything! :banghead:

No check engine light?

You can monitor the upstream 02 with a scan tool and see what it is doing. You can also unplug the upstream O2 and drive it. The computer will substitute a default of about .5 volts which is about the middle of the sensors range. Drive it and see what happens.

If it does it immediately after a cold start and never changes after it warms up than I would think there is an ignition or fuel delivery problem.

I don't remember if a 97 has a MAF sensor but if it does unplug it and take it for a drive and see what it does.

The light comes on while it is running real rough but doesn't stay. I will hook up the reader and see what kind of real time codes I get.

I will also try unplugging the sensors one by one and see if it makes any difference.

Thanks!

This sounds more like a fuel delivery problem. Have you replaced the fuel filter recently?

when the cat converters are replaced the engine must be checked to find the cause if plugged..this could be bad injectors.O2, or fuel regulator...even coolant leaks which damage the o2 THEN THE CAT CONVERTERS.

when you replace the cat converters you should replace the upstream O2 sensors ...as these if bad will destroy the cat converter....if replacing the total exhaust system this did not at anytime correct your vehicle performance it is possible its something else causing all this what dtc did you get with this ..

FINALLY FIXED IT!!!

It turned out to be a faulty fuel pump. It would maintain 60# of fuel pressure while it was ideling or running with no load but when more demand was called for it could not keep up. We found it by hooking it up to a machine that monitored pressure but could also bleed off fuel at the same time. Every time we began bleeding off fuel it would studder and die. We changed the filter first but saw no change. Then changed the pump and it was night and day. I have had this rig for 30k miles and it has never ran as good as it does now.

I put in a new Delphi pump. I have heard they are more dependable than other brands.

Thanks for everyones help.

FINALLY FIXED IT!!!

It turned out to be a faulty fuel pump. It would maintain 60# of fuel pressure while it was ideling or running with no load but when more demand was called for it could not keep up. We found it by hooking it up to a machine that monitored pressure but could also bleed off fuel at the same time. Every time we began bleeding off fuel it would studder and die. We changed the filter first but saw no change. Then changed the pump and it was night and day. I have had this rig for 30k miles and it has never ran as good as it does now.

I put in a new Delphi pump. I have heard they are more dependable than other brands.

Thanks for everyones help.

thanks for the feed back..

you went from excessive back pressure to a fuel pump pressure problem...

the person / business you used is incompetent !

find another repair shop that is qualified to make repairs on this vehicle.

how did he determine all this from his office chair ?

I did switch repair shops. That is how I found the real problem. The first shop tested the fuel pressure but did not test for volume. They figured if the pressure was there that the pump was fine. Then I think they were just grasping at staws.

I went back home over the holidays (200 miles away) and had an old friend, who runs his own shop, help me make the right diagnosis.

I did switch repair shops. That is how I found the real problem. The first shop tested the fuel pressure but did not test for volume. They figured if the pressure was there that the pump was fine. Then I think they were just grasping at staws.

I went back home over the holidays (200 miles away) and had an old friend, who runs his own shop, help me make the right diagnosis.

good move ...now this all makes sense...good luck...