1990 Ford Bronco II 4.0L Conversion - Engine Miss

[rpkline]

I'll apologize in advance for a long thread

Background: I have a 1990 Ford Bronco II that I went down the path of doing a 4.0L conversion on. I butchered the donor vehicle's wiring harness ('94 Ranger) after I got frustrated trying to figure out what was what. The vehicle sat for about a year and I finally thought the best approach was to just rewire the harness by hand.

I took the approach of running new wires from the PCM to the appropriate sensors one wire at a time. It may sound more complicated (certainly may be more time consuming), but it seemed easier and more straightforward to me.

Where I am now: I believe I have a "miss" on the left bank. There is definitely a miss at both idle and under load. The reason I believe it's coming from the left bank is that there was a very noticeable difference in the exhaust quality from the left side before I put in a y-connector at the inlet of the stock muffler. The right bank had a very smooth flow of exhaust vs. the left side which was erratic or popping if you held your hand up against the pipe on that side.

What I've done for testing: I replaced the plug wires after seeing two of them had wear through the outer sheathing - no major improvement. I put on a new crankshaft position sensor - no major improvement. New plugs - no major improvement. I tested the TPS and had about 0.9V at idle - need to check again though. I ran a compression test on cylinders 4-6 and came up with 175, 170 & about 172. I bought a HEI spark tester and had spark but at times it seemed to miss a cycle or two (was only testing the left bank). I have two new O2 sensors (only had one in the original exhaust and it was pretty old, so I got 2 new ones for this install). There are no O2 related codes. The PCM is a new refurb unit from Advance Auto.

My code puller stopped communicating with the PCM recently (doesn't sound good to me), but at the last read, I had no codes other than the neutral switch wasn't coming in. The PCM was reading lean on the left bank before I fixed an exhaust leak on the left side due to an indent in the header flange. Codes went away after this fix but the miss didn't.

I'm thinking at this point that it's something to do with the injectors on the left bank, or the coil pack, or the ICM. I also need to confirm the spark issue though to see if it's not consistent or if it's missing a cycle or two). I'm thinking it's not something like the IAC or MAF since the right bank (1,2,3) seems to run so smooth. Does the fact that the right side runs smooth rule out the ICM or the other items as I suspect?

I only have two items connected to the vacuum tree on the intake (master cylinder, fuel regulator and the PCV - did have this one disconnected for a little while with no improvement). No EGR on the vehicle.

Any thoughts or suggestions or additional questions would be appreciated. Thanks in advance. I'm not at wits end, but I'd really like to start driving this vehicle again.

 

[92exp4x4]

There were actually quite a few differences, at least in explorers, for the 91-92 years and the 93-94 4.0s. Ignition systems were a little different. I think the early ones were a batch fire system that would fire 2 plugs simaltaniously, one on compression stroke and the other on the exhaust. The later was more controlled I believe. Also the later systems used EGR and had 2 oxygen sensors, one for each bank, whereas the early had only one O2 sensor.

The '94 ranger 4.0 should have had EGR originally. Is your PCM set up for EGR? The ranger most likely had EGR like the Exs and will be tuned for it; if you used a 94 PCM.

Are the plugs motorcraft? Did you run the compression test when the engine was hot? Has the engine been apart? There is a specific sequence to putting the heads and intake on and tightening the fasteners. Also the Head bolts are torque to yield bolts and must be replaced EVERY time the heads are removed.

Could a valve be sticking, or not opening all the way? Hydro lifters can take up alot of slack in the valvetrain.

You may want to review the mechanical condition of your engine and start from there. Also do you have the EVTM manual and/or the schematics for the Ranger? Those will really help you engineer the harness to meet your needs. Choose a system based on your PCM, and start from there. The books are available on ebay, and are invaluable on projects like this

If you are getting compression and spark, the only other thing is fuel. You may have a clogged or restricted injector, I forget the exact resistence value for the injector coils, but some searching on this forum will net you the info. Fuel pressure should be about 35-40 PSI.

Good luck, I think patience and some perserverence is going to be needed in your situation.

 

[MrShorty]

I believe I have a "miss" on the left bank.

One of the first things I do when I suspect a misfire is to do a cylinder balance test. A '94 PCM can run it's own cylinder balance test, once you get your self-test system working again. A cylinder balance test will tell you if the misfire is isolated to specific cylinders or not.

One thing even the manuals say is that, because the PCM performs the cylinder balance test by disabling injectors, it may not be able to locate a fault with the injectors. You might want to also do a cylinder balance test by pulling spark plug wires, too to compare results.

 

[rpkline]

More info

I know the best approach isn't to list symptoms, but a few more points I observed on my ride home from work tonight. I was travelling up a hill at about 55 mph in 4th gear at about 2200 rpms. Everything was smooth and then every 10-15 seconds it would seem to just miss a cylinder.

When I turned down my road, I was going maybe 10 mph in 2nd gear and I decided to get on the throttle fairly good to get the rpms up more quickly (seems to struggle most when the rpms are below 2000 and under a light to heavy load). Once I got on it, it backfired quickly once and then I let off the gas and slowed it down. I assume this means it's running rich.

Hope this helps spark some ideas. Thanks for the two posts so far. I'm going to get my KOEO codes to see if they might provide enough info for someone to help me figure out why my tester won't kick my PCM into KOER mode.

Thanks again in advance for your input.

 

[rpkline]

I figured out why I wasn't able to run KOER tests. My KOEO codes included 522 which meant the PCM wasn't sensing the vehicle being in neutral. After fixing that code, I was able to run KOER tests again. This time, I saw 538-R only on the first time running KOER.

The 2nd time I ran KOER tests, I got 412, 411 and 538 again. All were labelled R. 538 was for no goose test. I guess I need to look at the IAC to get past this issue...could be my wiring too.

 

[rpkline]

I'm working on the cylinder balance test as suggested, but I think I need to clear up the 412 & 411 codes first for the computer to be able to control the RPM's where they need to be for the balance test (I assume).

 

[MrShorty]

For the KOER 538 -- are you performing the goose test when indicated? If you are correctly performing the goose test and you are still getting a 538, that might suggest a possible course of action -- probably something related to the TPS, MAF, or TACH.

One thing about the 411/412 codes -- the computer can be pretty sensitive to lopes when triggering these codes. Perhaps they are caused by and IAC issue, but it is just as possible that they are merely symptomatic of whatever is causing the engine to run rough. The other interesting thing is that they don't show up every time. That suggests that whatever is triggering these codes is at least somewhat intermittent.

Have you actually tried to enter the cylinder balance test, or is your assumption untested?

Also, where it is beginning to seem that your misfire is intermittent, a cylinder balance test may not give a good indication of the problem. I was thinking that the misfire was more consistent.

 

[rpkline]

Balance test

I tried getting the balance test to kick off but I don't believe it was successful. My Equus 3145 manual said it could take up to 5 minutes to see the codes for the balance test come back and I waited well over 5 minutes with no response to the reader. I'll test the voltate to the IAC to make sure it's not a wiring issue and go from there.

 

[rpkline]

Balance test #2

I forgot to mention that I didn't realize (when trying to run the test) that the rpms should go up to around 1700 for the balance test. I believe that's what I read after an internet search on the subject. From there, it's supposed to cut fuel out of a cylinder at a time. I'm not sure how that's possible with only two wires leaving the PCM to the injectors (one white and one tan).

 

[MrShorty]

I'm not sure how that's possible with only two wires leaving the PCM to the injectors (one white and one tan).

I must be mistaken. I thought all '94's were SEFI (one wire for each injector). If you really do only have two wires -- one for each bank of injectors -- then you don't have SEFI, and the PCM cannot perform it's own cylinder balance test.

 

[rpkline]

Primary Problem Solved

A little slow on my part to make this post, but I was able to solve my major problem (bad miss) after much work and cost. I did a lot of testing, rewiring, etc. but all of it was for naught. Most of the testing I did just didn't seem to confirm anything 100%. My solution came after continuing to search the internet for other people's problems and their solutions. I think the advice came from some threads on this site. I read some comments that Ranger engines seemed particularly picky when it came to spark plugs - they needed to be Motorcraft. I bought a set of six and the final plug I replaced (#3) fell out of the plug socket in pieces.

I thought I broke it trying to get it out as it was hard to access. It dawned on me that maybe I'd broken it when I dropped the engine down in the engine compartment. It was a tight fit and I must have banged it off the heater box or something. I think I still have a lean code, but my miss is long gone and the power seems very good. I had put new plugs in when the engine was on a stand thinking this was a smart thing as it was much easier than fighting the limited space in the engine compartment. Wrong

Thanks to those that tried to help. If anyone has any questions on my 4.0L conversion or custom wiring harness (if you can call it that), don't hesitate to ask.

RK