View Full Version : ECU questions
10-28-2007, 11:31 PM
Ok guys I have a quick question. I have a 94 Ranger that used to be 3.0 now swapped to a 91 Exploder motor with a frankensteined 3.0 ranger, 4.0 exploder harness.
Currently it has a 91 manual computer installed in it but I am converting the wiring harness over to a 94 ranger.
Question is, will a 94 4.0L automatic computer work with the 91 4.0L manual truck with the 94 ranger harness. In other words, does the engine ECU control the auto tranny?
10-29-2007, 10:13 AM
Yes, the '94 ECU (more properly called PCM, Powertrain Control Module)
controlls the automatic transmission.
ALL RBV computers back to 1985 when the A4LD was introduced do.
That is the least of your troubles....
An auto computer in a manual trans truck will set codes
for TCC and the over drive solenoid, but those will not
usually trip a CEL (check engine light)
OTOH a '94 4.0 computer is going to be looking for a camshaft position
sensor and a pressure feedback sensor for EGR that your '91 engine
simply doesn't have.
Not to mention the fact that a 94 computer is going to be expecting to run
the engine with 24lb/hr Disc-pintle injectors fired sequentially
rather than the 19lb/hr injectors you have now that are wired to
be fired in batches of three.
so to run with a '94 computer you have the wrong injectors,
the wrong upper intake manifold the wrong drivers side exhaust
manifold, the wrong on-engine wiring harness, as well as the
wrong computer you already know about.
BTW, what Y-pipe are you running on that 4.0? the 1990-1992 4.0's
used a single HEGO at the "collector while the 1993-1994 used
Dual HEGO's (seperate for each cylinder bank)
I think you have opened a large can of worms that you are never going to get
back inside the can they came out of.
IF the engine runs NOW I suggest leaving it alone, or failing that go
looking for a 1993 Ranger engine harness as that will only require the proper dual HEGO Y-pipe and switching out your "Grey top" injectors for the '93-94 "Red top" injectors to make it run right.
10-29-2007, 01:48 PM
Shit well then... I have found a 93 harness from a manual ranger. I guess I'll be going to pick that up asap. I am running a set of hooker headers with their y-pipe and have the drivers 02 bung plugged off with an old 02 sensor. So, for 93 i need the red-top injectors and two 02 sensors, I think i can manage that.
10-29-2007, 02:18 PM
Ok i've been thinking. The 94 ranger I took this off of did not have EGR, is there a possibility that it did not have camshaft position sensor? I'll look in my chiltons if I can find it, but where would said sensor be located? I just want to do a little homework before I do a lot of leg work. (93 harness is 150 miles away and i have to pull it).
Thanks again AD
10-30-2007, 11:23 AM
If the 94 donor didn't have EGR it also shouldn't have the cam sensor.
That's one thing about '93-94 ranger V. Explorer.
because the explorers (which were selling better) got the upgrades FIRST.
So while all 1993's got dual HEGO (some California 4.0's and even 3.0's got them in 1992)
And Explorers got SEFI in 1994 (EGR came with the SEFI), not all 1994 Rangers did.
And in point of fact some early 1994 explorers had EGR, while they didn't have SEFI...
That a further complication...
Look for the aluminum pressure feedback sensor (flat, rectangular aluminum module)
bolted to the drivers side of the upper intake right next to the EGR valve
Also look for the rusty metal EGR pipe on the drivers side exhaust manifold
It's also easy enough to reach back behind the intake on the donor vehicle and see if there is anything other than a simple oil pump drive in what would have been the distributor hole....
Mabey EGR/SEFI was cali-only on the 1994 rangers.
I've seen too many 1994 SEFI/EGR explorers to know that they weren't usually SEFI, but ALL 1994 Explorers do have EGR, that's easy to see at a glance.
I don't stick my hand back and check for a cam sensor
on any but a very few of them
10-30-2007, 12:41 PM
Ok i'll check the harness and make sure it isn't expecting a cam sensor. Then I'll figure it out from there.
Thanks again for your help AD
10-30-2007, 09:34 PM
The '91 engine will not have one, No '91 4.0 does.
infact until 1994 no 4.0 does.
What I'd be concerned about is trying to make a '91 engine
run with a '94 harness and PCM that are expecting to find a synchronizer
11-01-2007, 02:29 AM
Ok well I just spent about 3 hours labeling all the connectors on the 94 harness. The only things I dont have that are on the harness are the A/T connections mentioned before and the AC connections. I checked on both the wiring diagrams for 91 explorer and 94 ranger to makes sure all the same sensors were there, and I also checked visually as I was labeling the connectors.
What synchronizer are you refering to? I have not seen any in the wiring diagrams or by checking visually.
I'm planning on installing it early next week with the 94 pcm, I'll let you know whether it works or not (hope to god it does).
One last question before I dive in here, does the auto trans pcm have a different tune than the manual? I seem to remember reading something about that a long time ago when I first did the swap. If so I'll be looking for a manual trans pcm.
11-02-2007, 07:44 PM
1990-92 would have a different computer as well as a different cam for 5sp Vs auto.
BTW, I think the 1993's and Non-SEFI 94's are the best of the bunch.
11-07-2007, 05:14 PM
Ok well I installed the 94 harness and computer. So far so good. I am throwing three auto transmission codes but no check engine light. The only thing i notice is that the tune on the 94 ranger auto trans computer is different than that of the 91 explorer manual computer was. It feels like the timing advance kicks in much later and my compression braking is all but gone. Oh well it seems much smother all around. I'll probably look for a 93 manual explorer computer assuming it runs the same sensors and such.
Thanks for all the info AD.
11-08-2007, 11:11 AM
The auto trans computer essentially will not engine brake.
The auto trans computer needs to maintain idle to keep the transmission pump working.
The manual trans computer will much more actively cut injector pulses when the throttle is closed.
which is one of the primary reasons I usually suggest a manual computer.
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