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View Full Version : Custom build 1990 Mustang stock injection need help



Ruffy
05-18-2012, 03:00 PM
Hello all i am new to the site. I didnt know if i should of posted this in the Gm or Ford section but being the injection is from a 1990 mustang i will give this a shot.

Ok my build. 1984 Pontiac Fiero. Motor is a 1993 Cadillac 4.9 complete from pan to intake. Fuel injection is from a 1990 Ford mustang HO 5.0/302 from throttle body (custom plate made to fit GM intake) down to a new computer system.

Funny build huh? Well anyhow it works! But I am having a small issue that I want to get rid of. So far all the sensors are brand new and been replaced but the mass air flow. The issue are the idle. It dont like to idle the same every time. Most of the time when I come to a red light or stop sign the idle drops so low it stalls. To keep it from stalling i put it in neutral and when i take off I have to give it a small amount of gas and put into gear. It almost sounds like I put a 480 lift cam in it sometimes carrying on jumping and what not. It never blows black smoke. Also when going down the road it loses power! I know for a fact it has to do with the fuel system because that's what it feels like. It feels it don't get enough fuel some times.
I think it might be the mass air flow but I don't want to spend $200 and that not be the problem. I have a video on youtube called Ruffy,s V8 fiero throttle body and computer for a small look.

RobertISaar
05-18-2012, 04:31 PM
wow, that is an odd combination of parts...

seeing that it's run by the ford computer, this is the correct section.

you have any way of datalogging it to see what's going on in the near-stall conditions?

Ruffy
05-18-2012, 04:34 PM
No I dont. I wish I had the extra money to get a tool to tell me the error's that's going on.

34blazer
05-20-2012, 09:20 PM
yeah ditch the EEC and grab a 7730 lmao. jk. ever tried EECtuning.org?

EagleMark
05-20-2012, 10:05 PM
No I dont. I wish I had the extra money to get a tool to tell me the error's that's going on.Most auto parts stores will do that for ya...

cmaje72
05-21-2012, 07:47 AM
Some questions. What is your fuel pressure? What injectors? What EECIV manual (A9L) or auto (A9P) or something else? Is it a manual or auto tranny? Do you have a VSS wired in?
If you are using a manual ECU with an auto tranny and no VSS you will get those stalling issues like you described. I had this issue when I switched over to an auto tranny. I switched to the auto EECIV and it worked good with no VSS. It still idles down pretty far when coming to a stop but doesn't stall. This is on a 5.0 though. How did you get the pip signal from the caddy ignition?

jameslleary
05-21-2012, 08:38 AM
You can pull codes with a paper clip or jumper wire. You can also use a test light in place of the VOM. This diagram is from the Charles Probst book:http://i144.photobucket.com/albums/r183/jameslleary/4df4fea8.jpg
And, may be a stupid question, but did you modify the Injector harness to acommodate the Caddy firing order? Also, make 100% sure that you have the Hegos on their correct banks? Questions from my past experiences, I started on mustangs. Also, did you pull the system from a mustang, or is it a set up that you bought from someone...there are 2 firing orders for ford 302's.

Six_Shooter
05-21-2012, 09:21 AM
Firing order of a 302 won't effect how a Caddy 4.9 runs. ;)

34blazer
05-21-2012, 09:26 AM
Firing order of a 302 won't effect how a Caddy 4.9 runs. ;)


even though the EEC has sequential injector pulses?

Six_Shooter
05-21-2012, 09:31 AM
even though the EEC has sequential injector pulses?

To me "firing order" is ignition side.

"Injector order" is different. ;)

jameslleary
05-21-2012, 09:45 AM
To me "firing order" is ignition side.

"Injector order" is different. ;)Fine, Injector order...nit picker!

EagleMark
05-21-2012, 12:26 PM
The SFI may effect idle or could be turned off, not sure how newer cars work but the LT1 is only SFI in idle very low RPM, then batch fire. Just not enough time to fire each injector at higher RPM with cars of this era.

Are newer cars sequential at more then idle RPM? I was told that idle emmisions was only reason for this at time, had no impact on drivability or performace cause there's just not enough time to turn on/off injector for each cylinder.

RobertISaar
05-21-2012, 12:34 PM
The SFI may effect idle or could be turned off, not sure how newer cars work but the LT1 is only SFI in idle very low RPM, then batch fire. Just not enough time to fire each injector at higher RPM with cars of this era.

Are newer cars sequential at more then idle RPM? I was told that idle emmisions was only reason for this at time, had no impact on drivability or performace cause there's just not enough time to turn on/off injector for each cylinder.

don't suppose you can throw 2 injector circuits on a scope and confirm this? seems odd that it would switch out. my 95 MC should be SFI at all times, but i don't have a scope to confirm it.

i made a thread on 60V6 about the differences in single fire MPFI, double fire MPFI and SFI.... it wouldn't bother me one bit if SFI had yet to be invented.

Six_Shooter
05-21-2012, 12:49 PM
From many years of SFI discussion it seems that most manufacturers switch between SFI and batch fire at around 3000 RPM.

EagleMark
05-21-2012, 02:02 PM
There is a Constant in TunerCat $EE I do not have in TunerPro $EE which would tell us when it happens in an LT1 called :

"Individual Cyl. Fuel Trim Disable %TPS"

RobertISaar
05-21-2012, 02:07 PM
individual trims are used for commanding slightly different BPWs for each cylinder, not a SFI->MPFI transition. IIRC, EE has two individual cylinder trims, one for idle and one for non-idle? that constant is probably used for switching between the two.

Ruffy
05-26-2012, 09:18 AM
Some questions. What is your fuel pressure? What injectors? What EECIV manual (A9L) or auto (A9P) or something else? Is it a manual or auto tranny? Do you have a VSS wired in?
If you are using a manual ECU with an auto tranny and no VSS you will get those stalling issues like you described. I had this issue when I switched over to an auto tranny. I switched to the auto EECIV and it worked good with no VSS. It still idles down pretty far when coming to a stop but doesn't stall. This is on a 5.0 though. How did you get the pip signal from the caddy ignition?

Back to the VSS thinger. No mine isn't plugged in nor is the speedo plugged in. I think that VSS has 4 or 5 wires and is a round shape plug. The funny thing is not only coming at a stop does it do a low idle but also going down the highway it boggs some times like its not getting much fuel. Would the VSS wire do that also?

cmaje72
05-29-2012, 01:50 PM
I doubt it. I do not have a VSS at all and I have no other issues. My setup is on the engine that it was designed for though. You have such an odd combo of parts its hard to trouble shoot anything without the ability to datalog. I am curious why you didn't just use a GM EFI system.

Ruffy
05-29-2012, 06:16 PM
I doubt it. I do not have a VSS at all and I have no other issues. My setup is on the engine that it was designed for though. You have such an odd combo of parts its hard to trouble shoot anything without the ability to datalog. I am curious why you didn't just use a GM EFI system.

Yea it would of been nice to have the computer and all GM instead of the Ford swap. The guy that built it said he did it for better performance. The stock GM one lagged a little and the throttle body is smaller so that's why he changed it.

Stern90LX
06-27-2012, 02:33 PM
I joined just so I could reply to this thread. But after having taken a look around I think I may throw my 2 cents in a few more places here. :)

Anyway, the problem Ruffy lies in that if you are using the stock Tune on the EEC-IV for that Caddy motor you have to know that that tune was specifically written for a 302. Things like Injector Slopes, Injector Break Points, Throttle Body Air Flow, MAF Xfer table, Injector Timing, Intake Fill Rate(and a few I know I'm missing) all play in idle quality. Simply that EEC-IV was not designed to work on that motor even if you have all the correct Sensors and Injectors. The Air Flow design of that engine is going to be way off from that of a 5.0HO. You will need a EEC-IV Emulator chip like the QuarterHorse so the tune can be modified if you plan on keeping it.

See: http://www.moates.net/quarterhorse-for-fords.html