What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

1990 Full size GMC Jimmy problems.

R

rmbarnes

Registered Member
Joined
Sep 9, 2012
Posts
5
Reaction score
0
Location
Alabama
I have a 1990 GMC Jimmy with 5.7 TBI motor. Someone took the Cat convertors off and put true duals with flowmasters on the vehicle. I rebuilt it about ten years ago and have put maybe 30000 miles on it. It started giving me a little trouble about a month ago. She has always run a little rich and loped a little at idle. I attributed this to the preconvertor O2 sensor and the lack of the cat convertor. The Problem: When I get the vehicle going down the road at a normal operating speed 55 or 65 mph she starts kind of lurching or off and on surging. If I step into the gas she smooth's right out no hesitation. She takes the gas well and passing gear kicks in etc. If I let off the gas she also smooths right out. I replaced the plugs, wires, dist. cap, rotor button and even the u joints. The problem still remains. I had a shop put it on the computer and do a diagnostic on the vehicle and no problem found. I did the assembly line diagnostics with a jumper wire to A and B and I got code 13 and 44 which I think means it is running lean. So maybe my O2 sensor is bad. Would it make my vehicle lurch like this at 55 mph? I am stumped and need some help. Thanks in advance for any ideas.
Robbie
 
Both of those codes refer to the O2 sensor.
Trying a new one would not hurt.
Also checking and cleaning/replacing the EGR valve.
 
Or if you have headers and the O2 sensor is too far from the engine it might not be at the correct operating temp. A heated O2 sensor would solve the problem.
 
Don't throw any more parts at the problem. Figure it out then replace whats actually bad.

First, have you checked for vacuum leaks? Your issue could be related to that, very common for the TBI base gasket to leak, but I've also seen loose intake manifold to head bolts.

If that shows nothing, I'd disconnect the EGR valve (either via solenoid or the vacuum hose and plug it) and see if the cruise problem goes away. But I'd start with the vacuum leak, as that can cause a lean condition.

O2 sensor doesn't care about the converter.
 
True, the O2 sensor doesn't care if you have a converter or not...but if it's bad it will cause the engine to run poorly under certain conditions.
 
If the O2 is reporting a lean condition, when the vehicle is running incorrectly, my first inclination would be to think the O2 is good, and it is actually reporting the problem that it is seeing. However, that's just an assumption.

Watching what the O2 is doing under other conditions would give you a good clue if its likely O2 or not, and you'd see a vacuum leak via MAP readings as well.

Could be something as basic as an exhaust leak forward of the O2, or simply the O2 sensor.
 
last resort

after doing all the above mentioned -- fuel filter ?
 
He mentions that it smooths out under acceleration. I don't know as I've ever seen someone say "my fuel filter was garbage, and it acted just like..." but I would think under heavier fuel demands, the engine would run worse if the filter was the issue?

Since I cannot recall someone saying they cured a problem like this with a fuel filter, that's all I can base my thought process on.
 
?

fuel filter--Happened with one of my other cars FI Volvo 1800--
Just a shot in the dark--
 
Thanks for all the ideas. I still have not found the problem yet.

The O2 sensor codes show lean but the vehicle is idling rich not lean.
I have factory manifolds with no exhaust leaks.
I have not changed the factory location of the O2 sensor.
I changed the fuel filter when I tuned it up a couple weeks ago.
I will check for a vacuum leak this weekend and will also try cleaning the EGR cause I have never done that.

I did change outer wheel bearing on the drivers side of the rearend a couple months ago. Maybe I got something wrong there? I did not have any problems doing it and its not the first time I have done something like this.
Thanks again for any ideas I am lost here.
 
Also the vehicle has always idled rich ever since the convertors were removed and its never caused problems like this.
 
You can't use your nose to figure out rich, and the narrowband O2 sensors aren't any good for that sort of stuff either. They are *accurate* at 14.7:1 AFR, and nothing outside of that. That is why wideband O2 sensors are essentially a requirement of tuning an EFI vehicle...they actually work outside of 14.7:1

Particularly when catalytic converters are removed, a vehicle may smell rich/obnoxious, when in fact its fueling is no different than it was before.

Just do a real thorough vacuum leak/hose inspection, wiring connectors, etc. When you find the problem and solve it, the other things will likely go away.

An ALDL cable and laptop are all that are needed to "look" at everything your ECM is doing, if you find no EGR/vacuum issue.
 
Thanks everyone for the advice. I had a small hose that went to some type of smog canister. It had come off and was also collapsing. I replaced the hose and I also put a new O2 sensor on the blazer. Problem solved. Thanks I needed a fresh perspective and a little guidance.
 
You must log in or register to reply here.

Latest Posts

Top Bottom