Troubleshooting Advice

[FirTree95]

Hi everyone, I'm new to the forum and I'm hoping for help with an ongoing problem. First off, the specs for my truck are 1994 Ford Ranger STX 4x4 4.0L V6 engine. The problem I've been having is tachometer going out or reading erratically along with some unusual engine noises/rough idle. When I try to drive it I can't get it up to speed, but sometimes the engine surges and speeds up slightly. I took it into a trusted mechanic and he diagnosed bad 02 and MAF, and replaced both, which made sense considering I got codes on my Ford OBD 1 for running lean. This fixed everything initially (except a surging issue I later found out goes away if I don't use the defroster). A couple weeks later the problem came back, and when I ran an OBD test I got codes for running lean, 212 c (Ignition Diagnostic Monitor SPOUT Signal Grounded), 226 o (EDIS/Crankshaft Sensor Problems) and 232 c (EDIS Coil 1,2,3 or 4 Circuit Fault). The EDIS module seemed like the likely culprit, and also deciding the same the same mechanic replaced the EDIS module. Everything was fine again for almost a month, but then the problem came back and then went away again.

Knowing it was likely to get worse again if I didn't do something I ran codes again and did some research. I got 226 c again and the symptoms seemed to fit a bad crankshaft position sensor I replaced that (the old one was pretty dirty and beat up). My truck started rough after that, but ran really well for a few days afterwards. Then the tachometer went out again about three days ago, and my truck's engine made a loud knocking noise and then wouldn't start. I started it up again to warm it up for an OBD test yesterday. I got 212 c, 226 o and 232 c. It sounded good at idle and the engine revved up smoothly although I still had no tack/intermittent tach function. I just checked my battery with a multi-meter since it's pretty old, and the voltage was perfect. Tested my throttle position sensor since it seemed possible that would be related, but that was also functioning great.

I'm still thinking the problem is electrical since the engine sounds good at idle most of the time, and my truck has functioned well mechanically for pretty solid stretched between sensor and module replacements. I'm inexperienced with mechanical/electrical repairs, but I'm going to explain my theory so some more experienced folks on the forum can hopefully give some input. My understanding is that the crankshaft sensor sends data on the crankshaft speed to the EDIS module, which then sends data to the tachometer on the dash to show RPMs and data to the coil pack to control ignition/distribution to the sparkplugs and cylinders. Because of that, I'm thinking the problem isn't the coil pack because the idle isn't bad, and by the time the coil pack recieves its information the information being sent to the tachometer is already travelling through separate wiring (so a bad coil pack wouldn't correlate with tach problems). So the most obvious source seems to be the EDIS module or crankshaft sensor. The EDIS module is new and the crankshaft sensor is new, so I'm thinking the problem must be with the wiring between the crankshaft module and crankshaft sensor or with a fuse or connection somewhere completely different that's related to the crankshaft sensor and EDIS module. I'm pretty out of my depth, so I'm wondering if my theory makes any sense or if I'm missing something big here. Sorry for the massive post, but I'm hoping more detail is better, thanks!

 

[franklin2]

Your thinking and theories are sound. This is a intermittent problem, so it's going to be hard to find. If you can mess with it while it's running (watch out for the fan and the belts) pull and wiggle on the wiring and see if it makes a difference in how it runs. Pull on the wiring at the connectors and wiggle it around and try to find any thing that may make it throw a fit.

 

[bobbywalter]

follow and inspect the 4 wire from the pcm and the idm from the tach out to the coil-pack and edis.

sounds like a classic grounding issue internal to the board to me. maybe a bad tach...as a coincidence to the other failures.

this is a reason to make a case for mega squirt. starting over fresh.

 

[FirTree95]

Thanks guys. This is some useful stuff to work off of. Yesterday I started her up and after brief initial loss of tach function she ran and drove great with a working tach. Still running/driving great today. So I'm gonna count my blessings for now. Still planning on checking out the wiring best I can and seeing about the grounding. But considering I really don't know my way around truck electrical systems all that well I'm worried about hitting a wall again if the problem comes back. Would it be worth taking it to a dealership or mechanic in your opinion(s)? I'm wary of taking it in at this point because I suspect most mechanics won't be able to find the problem and will just want to throw parts at it.

 

[franklin2]

I'm wary of taking it in at this point because I suspect most mechanics won't be able to find the problem and will just want to throw parts at it.

That's what is going to happen since your problem is so intermittent.

 

[FirTree95]

I suspected as much, I'll just keep working on it and hope my luck holds in the meantime. Visual inspection of the wires and checking grounding is gonna be the first step. Somebody on another thread recommended opening up the engine computer and checking for corrosion, so that's a good next step if the wiring/ground looks ok. Thanks again for the help!

 

[franklin2]

I suspected as much, I'll just keep working on it and hope my luck holds in the meantime. Visual inspection of the wires and checking grounding is gonna be the first step. Somebody on another thread recommended opening up the engine computer and checking for corrosion, so that's a good next step if the wiring/ground looks ok. Thanks again for the help!

Just don't look at the wires, pull and wiggle them with it running. Since you have a 1994 I am assuming you still have a EECIV system. That system has a "wiggle test" where you can put the computer in a mode where it monitors all the input signals with the engine off, and you go out and wiggle and pull on the wires. If it sees any glitches, it alerts you to this. If you google "eeciv wiggle test" you can probably find out how to enter that mode.