Need Help Troubleshooting Tach and Stalling/Engine Power Problem

[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!

 

[RonD]

Welcome to TRS

O2 sensors are like batteries, they only last so long and the chemicals get used up
O2s need to be replaced every 150k miles or 12 years, period
This is the only sensor that wears out for sure, my 1994 4.0l has all original sensors except for O2s
Batteries last 5 to 7 years, just FYI


Crank sensors and EDIS-6 modules rarely fail, which isn't never but just unlikely
The tach signal comes from the EDIS module, its also the signal used to spark the coil and tell computer when to open fuel injectors
So yours reads like a wiring issue, not a device issue especially since you changed both EDIS and crank sensor

Your best bet at this point is to pull out the engine computer, its in the engine bay drivers side down low, between firewall and inner fender, not hard to do

And open it up and have a look inside, there can be some corrosion that will need to be cleaned off, also the 3 blue capacitors should be changed, they tend to leak after 25 years or so, and these capacitors could be part of your issues
Also look at the 60-wire connector and pins for corrosion

Pull off the connector for EDIS module
Test each wire from EDIS to Computer to see which wire is not working full time

drawing 1 shows the wires to check, "ignition control module" is the EDIS-6

 

[FirTree95]

Thanks! I appreciate your advice because I'm new to truck/automotive electrical systems and am basically starting with zero knowledge. Sounds like the 02 sensors needed replacing anyway because I think they were pretty old/it took care of my running lean codes, and the old EDIS module apparently had water in it and corrosion inside. The crankshaft might have been a waste, but at least it was cheap since I did it myself. I'll have to check out the computer and EDIS connections because I really want to take care of this for good. On the bright side my truck has been running great since yesterday, but I have a feeling it won't last.

Couple questions about the options you mentioned. When I open up the computer I'm assuming I should disconnect the negative terminal on my battery first, but is there anything else I should look out for in terms of damaging the computer when I clean/inspect it? And for the corrosion would you just recommend a soft brush or shop towel? I'm assuming I don't want any liquid cleaners or metal brushes in there.

What voltage setting would you recommend on the multi-meter? Would it be the same for every connection? And what sort of readings should I be looking for? And would the basic steps be to ground my multi-meter to the negative terminal, keeping the positive and negative terminals on the battery connected and the key on, and just go through the metal connections with the positive wire on the multi-meter?

Sorry about all the questions, and no worries if you don't have answers to all of them. I'm just hoping to find out what I can because the internet and my Haynes manual have proven kind of a dead end on most of this so far.

 

[RonD]

Yes, always disconnect 1 battery cable when working on anything electrical, when changing light bulbs its a judgement call, lol, but it certainly won't hurt

But for sure when pulling computer or any other module

Inside of computer should look like this: http://www.auto-diagnostics.info/ford_eec_iv

Clean, no corrosion
No, you can't hurt anything these are not "delicate" electronics, they are build solid for use in a car/truck, so not a residential computer, when was the last time a computer you had, or phone, lasted over 25 years, lol

Isopropyl alcohol and brush, and/or Qtips to clean off corrosion
isopropyl alcohol has little water in it so won't leave a residue behind, use at least 91%, 99.9% is better

You can use a towel to wipe off after adding the isopropyl alcohol, just make sure its a CLEAN towel, and dirt means there is SALTS and salt cause shorts in electrics


Most multi-meters have AC or DC voltage selections, some have Voltage levels as well, you want DC voltage and 20vDC if that is a selection
Vehicles use up to 15vDC

You test YOUR battery voltage FIRST
Remember it, like 12.5volts
When you are testing positive wiring then you should SEE 12.5volts, if you see 11volts then there is a problem

So YOUR battery voltage is the "baseline" voltage on that day of testing

A lot of voltage issues in vehicles are from faulty Grounds, a ground is the negative battery terminal
Most of the metal in a vehicle is connected to the negative battery terminal in some way

When you test battery voltage also test the Ground
Leave red meter probe on battery positive
Then put black meter probe on an engine metal part
Should see EXACTLY the same voltage, 12.5v if thats what it was
Do the same with a bare metal bolt on the inner fender or Rad support or Firewall
Should all read exactly the same as if testing on battery negative post


OHMs is another way to test wires
Select 200 OHMs, or lowest OHMs there is on the meter
Touch the 2 probes together
Meter should change to 0 ohms, then means the resistance between the red and black probes is 0, a direct connection

Touch the two probes to two places that are bare metal on the vehicle, should see 0 again or under 3, because both places are connected, grounded together

So OHMs is a way to test a connection, this can come in handy when testing the two ends of the same wire.

Some times the two ends of a wire are to far apart for the meter to reach both ends
Simple, get your own 20ft long test wire to use
Put that test wire into the connector for the wire you want to test and bring it to the other end of that wire
Should see 0 ohms, its just a loop of wire

 

[FirTree95]

Thank you again! This is really helpful. I tested my battery voltage (engine off and engine running) and it was what it should be, but I'm definitely going to check the grounding now. It's a pretty old battery, so I was actually kind of surprised the voltage was good. Tips on checking the computer and wiring are a huge help too. I really appreciate it.