I have a 98 5.2L, and cant figure this one out. Runs fine when cold, but it seems once it warms up and goes into open loop it wont idle and it misses/backfires at anything about 1500-2000 RPM's, and gets worse as it gets warms.

Once in awhile it will throw and error up, intermitant loss from CKP, CMP i believe, which is the crank and cam sensors. But normally it wont throw a error out. no errors.

Heres what i did...

- cut off cat (it was glowing orange right in front of it, thought it was clogged)
- replaced crank sensor
- replaced cam sensor
- cleaned throttle body with cleaner
- new battery
- replaced coil
- replaced MAP sensor

Borrowed auto enginuity from a co-worker and up stream O2 sensor working as should .2v -.9v, TPS ranges from 11% at ilde to 71% WOT

Has 5V and signal wire going to TPS and MAP

I checked the service manual for all the inputs to the PCM when it goes into open loop, and the only thing i didnt replace was the TPS which seems to be working.

Ive been wondering about the PCM for awhile now, but didnt want to spend the money for a replacement one unless I knew that was the problem.

any thought?

Thanks in advance!!

 

I've seen security systems cause CKP codes to be thrown. If you have an alarm, especially aftermarket you may want to look into that.

 

It's most likely your pre-CAT O2 sensor. Replace it with a Bosch or a dealer, I prefer the dealer hands down.


The reason your cat was glowing orange is because of the large amount of un-burned fuel collecting at the front of the CAT and burning as that is what the CAT is supposed to do. The reason it runs great on cold start is because you are burning the correct stoichiometric (air/fuel mixture), which is approximately 14.7. When the motor warms up the stoichiometric mixture is too rich because it is not being told to change the mixture by the O2 sensor (Pre-CAT), so now you’re running at something like 15+ which is way to rich. The unburned fuel thus gathers in the exhaust and ignites causing the back fires from the exhaust.

 

hydrashocker,

You think its the upstream O2 sensor even though im getting a decent wave form ranging from .2V to .9V?

I had though it was the O2 sensor but once I put that scanner on, and I seen the wave form and voltage I thought that it couldnt be than, but you think different?

What do you think about Walker O2 sensors?

 

Just because the sensor has proper resistance readings, doesn't mean it's not messing up.

Going out on a limb on this one a bear with me. This isn't going to sound like it's related but trust me it is. This happened to me and had exact symptoms but I had a MIL intermittently. Check the pressure regulator valve on the backside of your power steering motor. Check to make sure it's clean and not leaking. If there is even a minute trace of fluid there, the reason your engine is acting all cooky is because of this.

The reason is because the wires for the exhaust O2 sensor system is right below it and leaking fluid (that is hot) may seep into those lines and cause a minor short circuit. This may not be a big enough circuit for the monitoring to show up, but shows up in the event of unburned fuel combusting in the exhaust.

 

WhiteWidow00,

Makes sense, but i just checked now, and the power steering motor is in front of the engine on drivers side, and right behind it is the exhaust manifold. The only pre cat O2 sensor is on the passengers side, right under the passengers seat, and the wiring doesnt go up toward the power steering pump.
I see you have a 5.9L mine is a 5.2L, are they setup differently?

 

No, they are not and yes I understand the O2 sensors are on the passenger side under the cab and the power steering motor is on the front of the engine driver side, but the wires lead up in a harness that leads right under the power steering motor. The 5.2 and 5.9 shares the same block and most of the parts are found in the same area.

 

the power steering switch and the o2 sensor share a piece of wire loom, if the power steering fluid leaks into this wire loom it can cause a short int he o2 sensors

 

Okay I spent some time lookin for the wiring, but cant seem to find any, except for the wire that runs from battery to starter.
When you say it is under the p/s motor, that is the box that has hoses going to it from the p/s pulley thats attached to the belt? And coming off the p/s motor is the shaft that goes straight to the firewall?

 

Being his is a 1998 they do not have the R&P steering. It thought that was only the R&P syle issue and not the older systems.

Anyway, I stand by what I said about the O2 sensor, replace it. As for your name brand, whatever, I just like what I like ya know.