Hi everyone! First time poster here, so please forgive me if I sound like a newbie. I have done some extensive searching here (and elsewhere) to try to find a solution to this problem, but I haven't found anyone with a problem similar to mine, so I thought it might be best to post this as a separate thread:
I have a 1994 Jeep Wrangler (4 cylinder) that is 'losing spark' / shorting out / stalling while under load (gears engaged). This doesn't seem to happen when idling and usually takes a few minutes of driving before this behavior manifests. When this behavior happens, the tachometer immediately drops down to zero, the Jeep slowly decelerates until the power steering shuts off and I come to a stop. I cannot immediately restart the engine once it has died, but it will usually restart after about 3-4 tries (sometimes it takes a little longer). Once it dies like this for the first time, it happens with increasing frequency (I can drive less and less before it dies again). It doesn't seem like a fuel problem because the engine doesn't sputter: it just stops, the tach goes to zero and the engine revs down until I come to a stop. And it doesn't seem like an overall electrical problem because the lights and radio continue to work after the engine shuts off. So I'm thinking that some component is just shorting out, but I have no idea what component would cause this behavior.
I've taken my Jeep into my local shop two different times but they haven't been able to reproduce the problem, so they say they cannot troubleshoot it. They have been very good diagnosing other problems with this Jeep and my other vehicles, so I have been very surprised that they haven't been able to diagnose this one. They haven't driven it around a lot, mostly because they don't want to get stranded anywhere, but I am fairly certain that they'd be able to identify the problem pretty easily now that it's consistently failing after just 5-10 minutes of neighborhood driving. But before I take it back to them, I'd like to see if there's something simple I can check and/or replace to see if it makes a difference. I have only limited experience with auto maintenance, but I am willing to try what I can or I can take it back into my shop and give them some direction or ideas that they can work from.
Here's what I've done so far:
Replaced spark plug wires and ignition coil
Secured battery ground to chassis and secured battery on battery shelf (previous owner had it rigged with a bungie cord)
So, Jeep Forum gurus, I ask for your humble assistance! Any idea what might be causing this behavior? Any simple tests I can perform to troubleshoot? Thanks in advance!
How do you know there is no spark when this happens?
Free things to try if you think it is electrical:
When you replaced the wires, did you pull the spark plugs to make sure they were clean? Fouled plugs can cause sparking problems too.
Clean the battery terminals with a wire brush.
Clean the wire terminals to the distributor
Use electrical grease at all wire terminals.
Non spark problems that could cause this:
Failing fuel pump - borrow a fuel pressure sensor from autozone to test it
Clogged Fuel Filter -change it, low cost, should do it anyway
Clogged air filter - change it, low cost, should do it anyway
Dirty throttle body - free, clean it with carb cleaner
Dirty MAP Sensor - free, Clean it with sensor safe carb cleaner
(also clean the IAC with carb cleaner while doing throttle body)
Failing CPS - difficult to test
Failing TPS - difficult to test
I don't know if spark is causing the problem - I just know what it sounds like (the engine shuts off and revs down, almost as if I had taken my foot off the gas or turned off the ignition).
All of your maintenance suggestions sound good, but I'm wondering if they're all potential causes of this problem. For example - could a clogged air or fuel filter cause this problem, where the Jeep just shuts off completely, intermittently? I could see how a clogged filter would cause sputtering or loss of power, but not sure if a complete shutdown would happen and I'm guessing that a clog would stay there and prevent me from restarting.
Anyhow...thanks for the ideas. Hoping that someone else will read my problem description and say, "Oh yeah, that exact thing happened to me. It was X, Y, Z..." I know it's wishful thinking, but that's all I've got!
Usually a clogged fuel filter or clogged air filter will cause loss of power rather than intermittent stalling. But if a lot of poor maintenance items combine than it can manifest itself as more serious issues. I always suggest starting with those things first because they are cheap and should be replaced anyway (you only lose a couple bucks and a couple hours by doing it).
Rough running and stalling can be caused by many things. Unless you have a good reason to suspect an electrical problem, I would look at the fuel pressure first. If it is an original fuel pump and the fuel filter wasn't changed regularly or if you run the jeep at low gas levels a lot it can fail randomly under high load. If it is the pump, the problem will get worse and worse. changing the filter will help clear it up for a while since you are reducing a large pressure loss in the system.
Checking fuel pressure is easy so it should be near the top of your list. Chasing electrical problems and vacuum leaks are more difficult so should be near the bottom of your list. Go to autozone and borrow their fuel pressure gauge. It is just a matter of attaching it to the shrader valve on your fuel rail. turn the key on and see what the pressure says. Turn the key off and watch the pressure over the next hour or two and make sure its not dropping. Next watch the pressure at high revs and make sure it does not drop. Then if you can, have someone watch the fuel pressure while driving. See if you can get it to stall even.
JeepinWV also makes a good suggestion, it could be a clogged cat. This problem typically manifests itself at high engine RPM and loads (like the problem you are experiencing). Tap on it with a screw driver and see if it rattles.
You should also check for vacuum leaks by spraying carb cleaner along the vac lines. If you hear the RPM change while spraying, you've found a leak. It may or may not be able to cause the problem itself, but can contribute to a rough running engine.
You just have to check the possible causes off one by one, do basic maintenance first (filters, check plugs, clean electrical terminals), then free diagnostics (fuel pressure test, tap cat with screw driver), avoid throwing expensive parts at it.
I finally had a block of time to work on this, so I thought I'd report back what I found:
1. I tapped on the catalytic converter with a screwdriver and it rang out very clear - no rattle.
2. I borrowed a fuel pressure test kit from Auto Zone and tested pressure multiple ways, following the instructions Mike134 provided above and using the instructions in my Haynes manual. Here's what I found:
-- After turning the ignition on and off several times, fuel pressure eventually rose to 34 psi and stayed steady, even after I turned the ignition and let the Jeep sit for at least 3 minutes. According to Haynes, this suggests that the fuel pressure check valve and the regulator are operating normally, but the pressure was a little higher than normal, so I proceeded.
-- I then checked the vacuum line attached to the fuel pressure regulator and noticed that it looked very cracked and brittle. As directed by Haynes, I removed it while the engine was running and the fuel pressure rose to about 40 psi. When I reattached the vacuum line, the pressure dropped back to 34ish, but the connection was not very airtight because of the condition of the rubber boot on the line, so I decided that I needed to replace the vacuum line before I continued testing.
3. I bought a length of tube from AutoZone and tried to replace the entire vacuum line, but the connection was not right on the back end, so I just replaced the boot the connects to the regulator with some of the tube I bought.
After completing this setup, I retested, with some strange results:
-- With the vacuum line attached, the pressure was a little under 30 psi.
-- With the vacuum line detached, the pressure did not change and remained at 30 psi. I plugged the end of the vacuum line with my finger and heard the engine change, as it had before, but the pressure never changed.
So...based on my Haynes manual, it looks like I may need to check the fuel filter next. I already bought one, so I am headed out to my driveway right now to try to replace it. Wish me luck! And feel free to comment if you have any other suggestions.
I replaced the fuel filter earlier this week and no change in behavior. So I drove around with a buddy of mine who grew up in a mechanic's shop so he could see it in action and when he experienced the failure, he said it didn't sound like a fuel problem. Unfortunately, I could only get it to fail once during our 20-minute troubleshooting session, so he didn't have a lot of ideas about root cause.
I talked with some co-workers and did some more reading on this forum and wondered if I might have a loose ignition housing that was being tripped by the weight of my keys. So, I tested today with only a single key in my ignition and found that didn't make a difference. But, I discovered something interesting:
If I drive normally and turn off the ignition, my Jeep shuts off exactly the same way as when it does when this problem occurs. So, I'm leaning towards a spark/electrical problem.
But here's the strange thing:
Once I got the Jeep to start failing today, it was failing very often. In fact, I barely got home because at the end it was dying every 20-30 seconds. I'd let it sit for about 20-39 seconds and then it would restart pretty quickly (after 1-2 tries), I let it warm up for a bit, and then I'd drive down the street and it would die again while I was simply accelerating through 2nd gear. I think it died 8-10 times like this, with a shorter and shorter time between failures. To make sure I got home, I decided to try to keep it in 1st gear and keep the engine load light and doing that allowed me to drive the final 2-3 blocks to my house.
So, Jeep gurus - any more ideas to throw my way? I have to believe that someone has seen behavior like this before. I'm crossing my fingers and toes now because I am at my wits end and my wife is telling me that it's time to get rid of the old Jeep. Can you help me save her???
Bill - the tach immediately drops to zero. No sputtering or rough running. It just 'shuts off'.
I cannot comment on the wife situation.
That tells you the issue is electrical. If it were fuel or exhaust related your tach would still work. So you have an issue with a bad connection somewhere or the coil etc. You need to know what the other gauges are doing. If only the tach dies and the other gauges still work then it is not the ignition switch and probably not under the dash at all. If all gauges die then probably a main electrical problem. See where I'm going?
Dodge did not build my Jeep.
1988 Wrangler,4.2L I-6, Howell EFI JP-1,GM HEI Ign, 5 Speed Peugeot, Zone 2.5" lift + 1/2" booms, BFG 31 x 10.5, Bestop.