jackal91

Hi everyone, New to this site, actually, new to Jeeps, Hoping to learn some things and keep this old GC on the road. So, here goes,,,,
Vehicle is a 1993 Grand Cherokee, 5.2l, 115K, ran good until last week when my son changed out the thermostat. after stat was changed, he was checking some other things and accidentally broke the PCV valve, and the engine quit, PCV was replaced twice and the engine would barely start, idled erratically and would die when put into gear. So the call goes out to Dad--HELP!!--. I've backtracked everything he's done to make sure that he did'nt create this and I've found that it will start and idle ok with the PCV valve removed but as soon as its put back in engine dies, pulled breather from other side, no help, there's lots of vacuum at the intake, hose is clear, fitting is clean, IAC cleaned and appears to be working, I can see it move with small throttle changes, TPS seems to be ok, throttle body is relatively clean, only codes are 12 & 22, don't think 22 would cause this. vacuum lines have been checked, nothing obvious, FWIW, fuel pum/filter replaced 6 weeks ago, lots of fuel at rail, I'm kinda stumped here....
Anybody seen this before? Any ideas?
Thanks in advance for anything at all,,,

XJRed96

your 22 fault is indicating a faulty coolant temp signal and could easily cause your running issues. make sure its connected and that the connector is ok. the computer uses the temp signal to control the fuel amount and ignition timing.

as for the 12 i'm not seeing that in my FSM are you sure you read the fault right?

jackal91

Yep, pretty sure it's a 12, I've checked the codes a bunch of time as I'm working thru this. Any idea what the resistance for the sensor should be at ambient temp?. I'm gonna guess that the sensor got damaged when the thermostat stuck closed
Thanks

CherokeeCountry

I'm going through the exact same thing right now on my 93 v8, minus the cooling system maintenance you and your boy did. Will idle for half an hour with good fuel, air, and spark, but will die shortly after hitting drive, and will barely restart and run erratically as all hell after that. Following this one closely, please post if you figure anything out! and I believe 12 is the "Begin test" code if memory serves.

dave1123

Make sure you've got the right PCV. If it's flowing too much air, the cold mixture may be right, but not when warm.

jackal91

I tried another PCV valve just in case the first was bad from stock, same result. Problem is that with PCV installed, it won't flow at all, it just chokes the engine until it dies.
I'll check the temp sensor this weekend after I get back in town and update this thread. Still looking for resistance values for temp sensor. thanks for input, anybody else got any ideas?

dave1123

A complete list of temp sensor values is on page 6-15 of the Haynes manual but I'll give you a couple;

32* 29,330 - 35,990 ohms
50* 17,990 - 21,810
68* 11,370 - 13,610
77* 9,120 - 10,880
86* 7,370 - 8,750

If you stick a 700 ohm resistor into the connector, the fan should come on high. That's telling the PCM that the engine is around 220*

IDK about the 5.2, but the 4.0 doesn't have a PCV at all, but a metered orifice instead. This means it's just a controlled vacuum leak!

XJRed96

i'm theorizing that the car is trying to run real rich based on the reading it is getting from the ECT. by introducing a vacuum leak via the PCV the engine is better able to compensate for the added fuel. but again just a guess.

jackal91

XJ, that makes perfect sense, its sure seems like its running rich by the smell of the exhaust and that's something I didn't get too wrapped up in. I'm going too change the sensor when I get home on Friday.

steamer1227

Hope you fixed your issue.

Code 12 - Battery recently disconnected

jackal91

Nothing yet, just got back in town late last night, getting ready to get after it, will post fix later

jackal91

Ok, here's the fix, my kid had knocked temp sensor loose when he changed t-stat, connector was just loose enough that it looked like it was on, plastic clip is broke, secured with a dab of rtv, codes cleared, and it ran like a champ after a short drive.
Thanks to everyone for their input/ideas. Thats why these forums work!!!