pro94lt

Well I don't know where to start, runs fine goes into closed loop and won't idle. my o2's are reading most of the time around 900mv's but will drop all the way down to 100 or so. where should I start? About a month ago i finally figured out after a engine rebuild that i had a burned valve now I'm fighting this. Where should I start to look or what should I do, It will be a year in may since my car has functioned the way it should. HELP

Injuneer

If the O2's are reading 900mV all the time, its either not in closed loop, its running pig rich, or the O2 sensors are shorted to high voltage. In closed loop, the O2 mVs should be cycling rapidly over the range of 0xx-9xx mV's.

pro94lt

well, most of the time they are around 900, I am pretty sure it well am sure it is running rich, I can see it go from open to closed loop on the autoxray, as soon as it hits closed loop it will start acting up, while looking at the scanner with the engine running one thing i noticed is right when it wants to die the 02 milivolts drop to 20 or so if i hit the gas it usually will pull out and rev with a delay, also when it is acting up when you hit the gas the engine does not respond for a split second or longer. It acts like the accelorator pump is bad. Threw some codes finally but I don't know if these have anyghing to do with my problem, codes 16, 42, 41, 36, 51 any thoughts?

bubba4

If my code info is correct /16= low resolution pulse not detected /42= Ignition control circuit fault / 41= No ignition circuit / 36= faulty high / low resolution pulse(s) / 51= Prom / EEProm error. LF

Guest47904

First reset all codes. Unplug an O2 and while it's running good, measure the voltage at the battery and confirm you have over 14 volts DC. Now see if it continues to run good even after it has reached operating temp.

I think your codes came up as a result of the engine speed getting too low and the system voltage went below 11 volts.

Let us know what you get.

pro94lt

I'll try and do that tonight, from a previous time when i had the scanner hooked up it was at 13.5 volts, is the scanners volt reading ok or do I need to test at the battery? Either way I'll unhook the 02 and test and see what happens.

pro94lt

I have around 13.5 volts which i got through my scanner, i unhooked each 02 sensor an it ran fine while either one was unhooked. One sensor is new,

pro94lt

And yes the mv's for the o2 sensors are rapidly changing they just seem to be on the upper end.

Guest47904

If it ran well with an O2 unplugged, it has a problem while in closed loop. So the problem is with monitoring and control. The next thing is to force the O2 connections to a low number and confirm it with the scanner. To do this you take a reading with the O2 disconnected. It should be near 450 mV. Now force the signal low by putting a jumper from the black wire, to the tan wire and the purple wire. The reading should be below 200.

mvvette97

I had the same problem with my 94 after I put headers on it. It would run good till it went to closed loop they would switch back and forth. Replaced the sensors and still done it. Now after I drove it for a while it would stop switching and stay in CL. It seems that with the O2s being so far back from the engine with headers that they seem to cool off. My car is stock other than headers and the wife drives it most of the time so I said hell with this and tuned it open loop all the time. Runs much better now. Just make sure ya have a wideband if you think of open loop tuning. I hear this is a common problem on some cars with headers but not all of them..

pro94lt

Speedy, do I jump the wires with the o2 sensor hooked up to the harness or unhook it and jump just the harness or does it even matter. I've never heard that when the 02's are put so far back because of headers it causes problems, anything to do about it? I would just take it to a shop but I don't trust or have faith in any of them.

Injuneer

The O2 sensors from 94 and up are 4-wire heated sensors. They usually don't have problems with being too far from the engine. The single-wire unheated sensors in the 93 do have that problem.

mvvette97

hmm, didn't know that. I wonder why my 94 has the problem then? My problem all happened after going with LTs

Guest47904

If they go to 450 when unplugged, then you jump the wires with them disconnected.

pro94lt

I jumped both sensors with them unhooked, each one went to 4 mv's also I found I had a exhaust leak on my egr crossover tube where it bolts to the header, I just fixed it where next?