Stumble under ANY load??

[DrYeRLiNt]

Both the T-birds and the Mustang GTs had 4R70W transmissions. Also, they both used 19 lb injectors, and I would assume the MAFs are both calibrated identically. I used the MAF off the t-bird, but the injectors are from a 98 GT (attempted that during the problem diagnosis process).

It's not behaving like one injector is clogged... it acts like ALL of them are. That's what's so bizarre. It idles PERFECT, but you go to step on the gas, and it stumbles between 1000-1200 rpms and starts knocking a bit so i backed off the throttle. I installed a wideband yesterday, and the car idles ~12ish but the AFR goes to 18 at WOT (was a very brief test for diagnosis purposes).

Since it has ~30 psi fuel pressure at idle and ~40 psi at WOT, I have to assume it's not the fuel pump, and since the pressure nozzle is after the FPR, I have to assume that isn't the culprit either....

The problem was present before I changed out the T-bird 19 lb/hr injectors to the mustang 19 lb/hr injectors.


I'm stumped.

 

[DrYeRLiNt]

Okay so I purchased a complete 96 GT engine harness/ECU harness/ PCM/CCRM/headlight harness/MAF/etc

They should be here by friday hopefully. The question I have though is this-

it's all from a 5 speed GT. I know I obviously can't use that computer since mine's an auto (but i intend to keep it b/c i eventually wanna do a t-56 swap). is the engine harness different from the 5 speed and the auto? does the trans harness connect into that or something different? Will i just have to save all of that for when i get a 5 speed or 6 speed to swap into the car? Thanks.

Im hoping this will solve any wiring issues and get me that much closer to my goal.

 

[nyuk98gt]

DrYeRLiNt:

I do not know if the engine harnes is different between the 5-speed and the auto. From what I have read on various Mustang boards (that's a disclaimer of sorts), there is a transmission harness that plugs into the engine harness and it (the trans harness) is either a 5-speed harness or an auto harness. Let me take a look at my Haynes manual (pretty reliable, imho) to see if I can find out the differences between the two harnesses.

Chris

 

[DrYeRLiNt]

Okay here's what I've been coming across so far...

The T-bird engine harness had connectors for the O2 sensors on it. The GT engine harness does not. From what I've found online, the starter harness is where the plugs for the front O2 sensors come from. I doubt this is my problem, but at least one of several. The car goes lean with throttle input not rpms, meaning if I keep the throttle input light and rev it... it only goes slightly lean (15ish), but if I give it even 20% throttle it starts climbing to pretty dangerous levels.

At Wide open throttle, the car doesn't even use the O2 sensors, so it can't be them (because I've tried that lol). It's not my fuel filter. It could be the fuel pump/fuel pressure regulator but I have my doubts because I'm getting ~30 psi at idle and ~40 psi at WOT. The TPS I did have to drill out the holes and adjust it ridiculously, so maybe that's bad? The IAC I cleaned with carb cleaner and cleaned the electrical connection with the electronic cleaner.

I need to re-run the codes on the car and go from there. I suspect the transmission harness is going to be the same deal as the engine, and that's giving me codes, but I have my doubts that that plays any role in my engine problems (unless these computers have some sort of limp mode, but running lean would sound like the opposite of a limp mode as you would want it to prevent detonation and keep the motor cool... by running rich).

How big of a vacuum leak would it take for the car to run lean? Would the smallest hole cause it to run lean?


Thanks guys

 

[Rusty67]

Take some carb cleaner and spray it all over the place while the engine is idling to see if you can locate a vacuum leak.

 

[DrYeRLiNt]

I tried that with little success. I was hoping to get a loaner tool vacuum tester at auto zone. Any idea if they have that?

 

[Rusty67]

Vacuum gauges are cheap at harbor freight. If you can't find them with carb cleaner then you provably don't have a leak but it wouldn't hurt to check with a gauge.

 

[DrYeRLiNt]

What should the vacuum read? This will only tell me from the throttle body on right? So if it were between the MAF sensor and the throttle body it wouldn't tell me anything?

 

[Rusty67]

I'm not sure what the normal PSI should be on a modular. I might be able to look it up but I'm not going to do it tonight. Maybe I'll check tomorrow if I have free time at work or tomorrow night when I get home.

You would not want to try to measure vacuum before the throttle body. There should be existing lines you can hook up to with a T-fitting or a plug somewhere on the intake you can use.

 

[DrYeRLiNt]

Update:

I traded it for a red 94 GT. No more worries