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93/94 ECM, cam sensor, EGR


Shran

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Helping a buddy here, his setup is an '89 Ranger with a 4.0 swap from a '94 Explorer. Explorer engine harness and dash harness were used. The engine itself was from a 1992 Explorer and was recently rebuilt by a reputable shop (all the usual stuff, bore, pistons, new heads, etc) and replaced the '94 engine that was originally in the truck, which ran fine but was rather high mileage. The EGR system and cam sensor from that engine were installed into the new engine.

The specific problem he is having is a hesitation right off idle. Once you get past that, it runs great. This issue did not originally occur with the new engine. He told me that they initially thought it was just the ECM re-learning a new engine or something related to break-in but it continued and now they have replaced the coil pack, injectors, MAF sensor, IAC, coolant temp sensor but the issue persists. I don't think he has pulled codes on it yet.

To me it sounds like the EGR valve could be suspect based on issues I've had with those before. He also stated that the engine builder dropped the cam sensor in without aligning it. So two possibilities to rule out there before anything else.

My question: I have an ECM from a '93 Explorer. That vehicle did not have EGR or a cam sensor. Has anyone tried using an older ECM with a newer harness/engine to eliminate EGR or a cam sensor or both? I am kind of assuming that the '93 computer would just ignore those two components? We are kind of just looking at all the options, if the ECM swap would effectively eliminate those things then it would be cheaper to go that route rather than throw more parts at it.
 


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RonD

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You can just pull the vacuum hose off the EGR valve and see if hesitation is gone

Yes, unplug the DPFE sensor and EGR solenoid, and unplug the Cam sensor, and try the 1993 4.0l computer
I suggest unplugging the wires because there may be internal software that might see the feed back of connected wires
But all the other wiring will be the same, EGR and Cam were added wires

On either of these computers I would replace the 3 capacitors just on speculation because they WILL fail after 20+ years, 0 doubt on that, you just don't know when, lol, and its under $5 to do it
 

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Thanks Ron, great advise as usual. I kinda figured that would be the case. Normally I like doing more troubleshooting but he's 35 miles away and the truck is kind of a hodgepodge of parts at this point (really my fault, I did the 4.0 swap years ago and sold it to him.) There are so many possibilities with all the parts swapping that has happened.

Wonder if I can get capacitors for it locally. I'll have to crack it open this evening and take a peek. I should just buy a bunch of caps and redo everything I own.
 

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For the caps you have to use the same uF value, like 16uF but you can use a higher voltage

Say one is rated 16uF at 36v, you can use a cap rated as 16uF at 50v or 100v as long as its an equal or a higher voltage rating its fine to use
Makes them easier to find, the black color caps are better but blue is fine

Caps are + and - so take pictures and make sure you get the polarity correct when reinstalling
 

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Yeah... I am quite familiar with recapping electronics, I have a pretty extensive old computer collection that commonly has both radial and axial caps (which fail rarely, but it happens) plus a variety of SMD caps in electrolytic and tantalum variants. The SMD electrolytic ones are the worst, you can pretty much guarantee that anything made before the mid 90's or so has already failed and needs replacement. Fortunately they're easy if you have a steady hand, I have done hundreds of them.

Most caps also have a temperature rating assigned to them as well... cheap ones will be low temp.
 

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California emissions engines were sequentially injected in those years, federal emissions engines were batch fire and the engine wiring harnesses are different. Could be part of the issue.
 

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So... when the capacitors go bad... what are the symptoms normally.

I searched @RonD posts and I didn't see what I was looking for... I believe he replaced them in his personal truck not long ago for a reason I can't remember.

Can someone help me out?
 

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There are no set symptoms outside of "something is wrong", lol

On mine, I think, it started with high and low idles AFTER warm up, but IAC valve and ECT both tested fine
Then I got stumbling at different throttle positions, after warm up
Then stumbling moved to any temp
MAF tested OK during this, and was cleaned

Then Fuel pump didn't come on with key on, I always listen for it, so no start, but if you cycled the key off and on it would start to work as it should, so rebooting computer worked
Then it would come on and stay on, not go off after 2 seconds, but I could drive it, except for the stumbling, lol, didn't trust it

This all happened over 2 months of odd occurrences, and CEL would come on and the codes were odd as well all through this time

2 of my caps were for sure bad, 3rd didn't look corroded but...............never tested it
 
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Thanks RonD...

That is kinda what I was gathering from the many posts where the capacitors were mentioned... just weird random symptoms.

I guess they're easy enough to look at and it's free to do so.
 

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As a follow-up to this:

The 1993 computer made the original issue exponentially worse. Why, I have no idea and the owner is not sure either. Disconnecting the EGR sensor, DPFE and cam sensor and swapping in the '93 computer resulted in an engine that sounded and felt like it had a really bad miss. Maybe the '93 ECM is bad, maybe there's something wired differently, I don't know.

I did replace the capacitors on it. They were not leaking and did not appear to be in failure mode to me but I don't really have a way to test them. I think it's important to mention here that the ECM circuit board and everything on it is coated with some kind of waterproofing substance - You have to burn through it with your soldering iron while removing and replacing components. It's kind of a pain in the ass.
 

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Yes, all the ECMs have a sprayed on coating to seal them after assembly, looks like overspray, was little white dots

1993 and 1994 used the same computers, by engine size and transmission type, only variations in those were the EGR/CAM sensor models required in Calif, I think another state may have also required it in 1993/4
 

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Second and hopefully final follow-up to this:

I had this truck at my house for a few days and we threw more parts at it. New injectors, ignition module, throttle body, some other random things. Zero change.

Eventually through some personal connections that my buddy has, he learned that it may simply need a tune programmed in for the new engine. The guy's theory (based on a bunch of other similar year Fords) is that the auto computer is expecting to see the 3/4 shift solenoid and torque converter and because they don't exist, it's freaking out and pulling out timing once the ECM goes into open loop. He said this was likely happening on the old engine too but was not obvious because it was built with slightly lower compression (stock) and was just tired overall.

The guy flashed an ECM for my buddy just based on a description over the phone and mailed it to him. Apparently there was a big improvement from just that and over the last week they met up in person and built another tune that was basically a complete fix. I have no idea what tuning setup he was using, I didn't ask.

Very weird problem and I was glad to hear that it was fixed. Having the right connections pays off I guess, I don't now anyone who would have been able to figure this out. I'm also curious what would have happened if we'd used this new engine in a 90-92 truck manual trans ECM that has no EGR, DPFE or cam sensor inputs.
 

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California emissions engines were sequentially injected in those years, federal emissions engines were batch fire and the engine wiring harnesses are different. Could be part of the issue.
Did you confirm the harness as this post mentioned...
 

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Did you confirm the harness as this post mentioned...
it should also be noted that if the wiring harness has connections for a cam sync and the egr system then it is a California emissions harness.
 

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I don't know what emissions system it has. I am under the impression that all 1994 Explorers had EGR, DPFE, and cam sensors, and that 93 was the weird year when some did and others did not.
 


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