Idle/too rich after T5 swap

[Blue coyote]

Sorry if I sound kinda moronic here. I usually stick to the MII section, but I'm having a problem with my daily beater...

Last week I blew the front seal out of the (weak-assed POS) A4LD in my 89 2.3 ragtop, and I had access to a 1990 2.3/T5 setup.

Swapped in the complete engine and tranny, since the old one was blowing a bit of blue smoke anyway. Still running the 89 auto PCM...

I've got it running now, but there are some issues. Most of them are minor and/or workable, but I'll list 'em anyway, in case they make a difference.

Oil pressure gauge reads zero, but I know it has pressure (or else it would clatter like a mofo at most RPMs, right?). The 90 had the small sender and I swapped the larger cannister-style from the 89 engine.

Temp gauge seems to read backwards (starts high, drops as engine warms up). It did this with both the old and new sending units.

Fuel and volt gauges read fine.

The big issue is with the idle and mixture. On start-up, it idles at about 1700, but when I drive it and come to a stop, it usually tries to idle at about 2400, and stumbles/hesitates under partial throttle when starting out. Sometimes it will drop back to 1700 and lose the hesitation after a while..

It got marginally better when I cleaned out the 89 TB and swapped it in (with the TPS and IAC)

One guy has mentioned that the PCM isn't reading the neutral switch input, but that seems odd to me. I didn't think the auto PCM would be looking for a neutral switch after start up...

I'm a bit hesitant to just swap in the 90 manual PCM, because I don't know if the pinouts are compatible (mostly because of the gauge issues leading me to believe the wiring might have changed) and I don't want to risk frying the system.

It probably doesn't help that I know SFA about EFI systems (the MII was always carbed...)

Any ideas?

 

[Blue coyote]

Well, not that asking here has been any help so far, but an update:

I swapped the PCM to the 90/T5 one and it ran like crap for about 15 minutes. Then it settled down a bit, but it still idles at about 1500 and full-rich.

Anyone have a clue, or am I better off waiting for another Mustang II guy (who happens to know EFI) to come over next week and help me figure it out?

 

[mustang_montana]

theres a vacuum line that runs to the A4LD, make sure you plugged that off at the vacuum tree in the engine bay cause i had the same problem.

**itll be about a foot long rubber tube just hanging off the vacuum tree, when i dropped my a4ld out it just slipped off and i didnt nottice it right away.

 

[Blue coyote]

I got that one before the engine went back in. It took me a minute of looking to find the vacuum leak I DID have, though. The line to the cruise control can under the dr. fender had pulled off at the valve under the wiring harness. I can't hear or detect (light shots of ether around the intake, lol) any current leaks, other than a bit of an exhaust leak still at the lower end of the manifold. Could they have made those nuts any more of a PITA to get a wrench on 'em?

Not sure if its part of the problem, but I noticed that the line running to the EGR solenoid is one of those pin-thin lines. Shouldn't it be at LEAST a 1/16th" inside diameter?

 

[mustang_montana]

i wouldnt think the pcm is your problem, i still run the automatic one for mine and it runs like a champ with the t5 now. id save it for last at least, theres gotta be another leak. your timming is good right? yeah those manifold bolts will be tough, im surprised mine isnt leaking there considering i basically used it to hold up the a4ld. anyway, a small leak there will cause issues with the 02 sensor being right there.

 

[Blue coyote]

Yeah, I'm 99.5% sure the PCM isn't the problem. I've run the codes using both the 89 A4LD one (8CB) and the 90 T5 one (8CC) and they both agree (other than the 89 PCM telling me the TC clutch isn't functioning )

I'm getting codes 51 and 83 in the KOEO test.

I'm getting codes 98 and 51 in the KOER test.

When I swapped in the engine harness from the original setup, I have two "extra" plugs. One is a long section with a small rectangular 2-wire plug. I think it ran down the tunnel to the A4LD somewhere, based on the amount of burnt ATF on the jacket of it. The other comes off the harness adjacent to the ECT sensor plug, and looks almost identical to it. I have confirmed that this plug does not exist on the '90 T5 engine harness, but does on both the 89 and a spare 88 engine harness from A4LD-equipped 2.3 engines. This one, I don't have a freakin' clue what it is or where it goes...

 

[Blue coyote]

I ran the codes again after swapping the plug I found onto the ECT sensor (leaving the other one disconnected since I have nothing else to plug it into).

KOEO codes are unchanged (83 & 51)

KOEO codes are now completely different: 13, 22, 34, 42, and 72

The idle is not better (1200-1500) and its pumping less smoke (but still a bit)