Hello,

This may be best posted in "engine swap" but there are some specifics about the 4.0L from the 1991 and 1994 model year that I need to discuss.

I pulled my 4.0L engine/trans combination out of my 1991 Explorer and installed it into a 1994 explorer (blown motor). No real issues with the mechanical conversion since I had plenty of spare parts. When I came to do the engine emission control electronics I knew there may be some issues. The connectors did not match as "quick connects". No big deal as there are two O2 sensors and additional throttle controllers on the upper intake (plenum) so I got set to install the entire harness from the 94. All connections match up except one (assuming I use the 1994 plenum).

The 1991 engine does not (seem) to have a camshaft position sensor (mounted on the oil pump top rear of the motor behind the ignition coil on the 94). It is a three wire connector.

I assumed the controllers on the 91 4.0L would be the same/similar to the 94 4.0L (except on the plenum and the additional O2 sensor).

I have the 91 PCM if I need to go that route and rewire the whole thing.

I am missing something here? Any ideas?

Thanks.

 

You are correct.. No cam sensor on the '91 or '92 (I only know those 2 for sure).. and also no knock sensor (that may not be have been used until until later than 94 anyway)..

I don't have a solution.. just letting you know you are correct.. '91 and '92 don't have cam sensors and I don't think you can add it in (but I'm not positive on that)


~Mark

 

i think that the 94's had a erg valve too

 

Thanks for the replies.

I pulled the valve covers and lower intake manifold off yesterday to have a closer look. There is no cam position sensor in the 91 motor but there is a syncronizer and shaft assembly in the block. I (think) I can install the sensor (and shaft assembly) from the 94 into the 91 motor. We'll see what happens.

As far as the EGR... I think you are correct but it was definately absent on the motor I pulled out of the 94. The previous owner had the motor "rebuilt" in 2003 because of catastrophic failure and it blew again in early 2004. When I pulled the motor apart there were a ton of issues with the way this thing was put together so no EGR was not too much of a surprise.

I wonder if it will ever run again!!

Any further comments, tips or advice would be appreciated.

Thanks.

 

You have created quite a little mess for your self haven't you. Well I've just completed a nation wide search (eBay) to find a new PCM for my 1993 Cal, manual trans Explorer. And this PCM was changed by dealer in 1995 under warranty to address a cold start issue. (New PCM richened up cold start A/F table.) So that made my PCM even more rare. My project is that I've sent the PCM to SCT so they can read it and burn a chip for me.

Enough about me. What I have learned in this process is that there are dozens of PCMs with different part numbers and with different calibration codes. Cal and fed are very different. 1991-1993 - all fed cars are multiport fuel injected. All 3 injectors on one bank fire at the same time. All Cal cars are sequential fuel injected. Just 1 injector fires at a time. And in 1994, fed went SFI too. So this is why your 1994 harness has 6 individual leads going directly to the PCM and the 1991 harness has just 2.

The 1994 PCM will fire your injectors one at a time. If you use the 1991 PCM with the 1994 harness, you will only ever get 2 injectors to fire. If you get the 1991 and 1994 engine control schematics, it is fairly self explanatory.

All the Cal cars have cam position sensors. This with SFI gives btter ability to control bad emmissions - Go Cali! Then in 1994, fed followed Cal so all cars got cam position sensors.

All cars, all years, also have the crank position sensor that you mentioned. They have to. This is how the car gets the first signal to start. With the ignition control module and ccrank sensor, the car has enough input to cause a spark withou the PCM. Once a RPM signal is received, the PCM uses the cam position sensor to massage the spark advance.

I would think your easiest solution is to pull the cam position sensor out of the 1994 block and stick it in the 1991. There is a cover you ned to remove and then it pops right in. Look up the alignement procedure for this. If you are off a tooth the car wont run right. Also, there might be a different drive shaft arrangement for the oil pump. I haven't had to take this apart yet so I'm not sure what it looks like. But check it our good first before you start so you know what you're getting into.

Then, use the 1994 harness and PCM. You will be converting over from MFI to SFI bu I think this is a better system even though many claim that MFI can poduce more HP. But since you have a 1994 body, it will be smog tested to 1994 specs and you'll have a better chance at passing running cleaner SFI. Besides, changing a SFI to MFI is actually illegal, at least according to CARB in Cal.

Which reminds me. Your state might require the EGR back on it. If you don't install it you will get CEL for 3 or 4 codes. If you get a custom chip, you can have the programmer turn off the EGR all together and then you wont get any codes. With my chip - I'm going to keep the EGR functional since it does help the environment and improves gas mileage while cruising. At wide open throttle, PCM closes off EGR all the way anyways so there is no power loss due to EGR.

But in the least - get those schematics. Does a world of good and you will now know what you are looking at.

 

That is what I'm going to try. Unfortunately the cam sensor from the 94 is damaged (electronic leads are broken off). I'll need to source a 94 cam sensor. We'll see how that goes.

The 94 unit slides right into the 91 block where the original oil pump shaft was removed. There is a nice description of the instalation in Haynes.

As for the EGR I'll have to take a look at another 94 to see what the heck I'm missing and how it is mounted!

Thanks for the feedback.

Gil

 

I can take a picture of my EGR and post it. I don't think anything changed from 93 to 94. Is the tube still there from the exhaust manifold to the EGR valve? If not, the manifold is either plugged or you have a huge exhaust leak. I'll try to remember to get a picture when I get home tonight.

 

Here's what it should look like. The silver rectangle thing with 2 rubber tubes coming off bottom is the DPFE switch that monitors how much exhaust gas is getting into the intake. To the right is the EGR valve itself, rusted as they get, and the vacuum actuated diaphram, silver. Just to right and down from EGR valve is the vacuum solenoid. This pulses with signal from PCM to allow more or less vacuum to the diaphram. Just below the oil dipstick handle is a silver heat mesh covered tube that runs from the exhaust manifold to the EGR valve. There is an oriface in it of a known diameter that allows the DPFE switch to sense the differential pressure across the orafice and then hence the actual exhaust gas flow. Simple huh?

 

So what happened Gil? Does it run now and what of the EGR?

 

Hello,

I have rebuilt the cam position sensor and re-installed it (I have yet to syncronize it). I rewired the main harness and built the top end back up. I still need to finish the re-assembly of the rest of the auxillary components before I can try to fire it up.

As for the EGR... I seem to have the DPFE switch but no EGR. Thanks for the photo. I'm still not sure where it is going to fit at the exhaust manifold. My 94 motor has a mounting on the maniford (what seems to be a port at one time) that was welded closed. Obviously it is not present on the 91 motor. Can you get a decent photo of the exhaust connection for the EGR? (although it looks like you have headers)

Is there a two wire harness attached to the EGR solenoid? If so what colour are the wires?

You have been a great help, thanks!

 

What did you have to do to the wiring harness? The 94 harnes and PCM are compatible, OEM.

EGR solenoid wires are Red and Brn/Pnk.

DPFE wires are Brn/Wht, Brn/Lt Grn and Gray/Red.

You'll need a new exhaust manifold if someone welded up the port. How dumb was that? It's just an NPT thread - could have used a NPT plug.

Yes I have headers but the EGR tube hooks up in the stock location. 50 state legal headers. I knew I should have kept the stock manifolds - could have sent you one. Tossed them out last year when I moved.

Maybe, you can drill and tap your 1991 manifold. I bet they are the same casting but just not tapped for non-EGR cars.

 

Some of the connectors and wires were worn/damaged and I had to create a new connector for the rewired cam position sensor so I basically "rebuilt" the wiring harness for preventative reasons.

I'll have a closer look at the manifold tonight and hopefully finish the re-assembly.

I'll post you tomorrow.

Thanks again.

Gil

 

So, here we go...

I have built up the top end. I have two connectors without a home. One is on the main wiring harness and has a red - pink/brn wire combination. It's routed so it hangs between the IAC and the DPFE. Sounds like the EGR connector. The DPFE is present and has the proper wiring and connectors. I also have a connector with a grey/yellow - red combination. This runs off the wiring harness on the drivers side (attached to) the wheel well with the bulk of the wiring going down to the two connectors on the transmission.

I'm reviewing my wiring diagrams as we speak!!

The motor turns over (which is a good start). I can begin to pull KOEO codes. I need to hang the exhaust, run the vacuum lines and re-assemble the intake housing (MAF etc) then I can get a better idea of where to go next.

Thank goodness this is a hobby and not a necessity! (for daily transport)

 

Double check that EGR wire again. i think you just misqouted. It should be Brown with a pink stripe, the other on red. Red one is 12 V power coming off the PCM. Brn/Pnk is the one that grounds out inside the PCM to activate the solenoid.

The only Gry/yel and red, 2 wire connector I see on the schematic goes to the canister purge solenoid. This is the gas vapor recirculation system. It is on the drivers side as you mention but has nothing o do with the transmission. The PCM controls this on/off based upon engine vacuum and throttle position. There should be a black canistor just in front of the brake master. If not - that got pulled too. Let me know what you find and I can take a picture of that too so you see what you'll need. This gets a little complicated too as there are vac lines that run from the canistor to the intake and back to the fuel tank. The repair manual should have a vacuum diagram.

 

I found that same wire combo on the wiring diagram too (evaporative cannistor purge solenoid). The cannistor is present on the vehicle but I still can't find the match to the connector (I only took a quick look). I need to find the solenoid and see if it matches up. It has nothing to do with the transmission but it happens to be wired with the same harness that goes down to the tranny (also an oil and h2o sensor is on this harness). The fuel line (ie. hose to fuel tank) and all the vac lines are present on the cannister.

I think the EGR wire combo you described is what I'm looking at (other connector with no home). It is present on the 94 harness but not on the 91.

Most of this is coming together. I'd like to see if it runs first and then address these other items. If I can get it running I can pull the codes and go from there. I need to find a 94 at a U-pull wrecker to replace the missing items.

It's no point spending too much money if I can't get the motor going. I still need to replace a rocker panel, do the brakes and swap some tires.