94 TB & TPS with 89 A9L - can't get 0.98v

[Wallyman]

Title says it all.. using an 94 engine (all stock) with TB and TPS and an 89 GT wiring harness and A9L. TPS voltage with key on-engine off reads around 1.25v, and I can't get it any lower... is it just as simple as elongating the two TPS mount holes so I can get it to the often-quoted 0.96-0.98v?

Just got it in the chassis and chasing a cold start issue, won't start cold without starter fluid. With enough screwing around it will eventually idle and once warmed up, it restarts without starter fluid but it's always idling around 1000-1100 rpm (granted I don't have an exhaust or O2's plugged in yet).

So, do I just auger out the holes and set it per the guides here?

 

[AeroCoupe]

First go here and it explains how to physically adjust it (scroll down to "2.) Defective TPS"):

Cranks OK, but No Start Checklist for Fuel Injected Mustangs

Cranks OK, but No Start Checklist for Fuel Injected 5.0 Mustangs model years 1986-1995 A word about this checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work...

stangnet.com

Then go here for the myth of as close to 0.99V as possible:

Mustang TPS Adjustment - 0.999999v not necessary

EDIT: This post applies to 86-93 5.0 Mustangs. Seems to be a common myth, so lets sticky a thread explaining how the TPS works. Jrichker has provided the basic TPS guideline to follow. But here's a snip of the A9L GUFB which is the programming logic. Pay attention to the part highlighted...

stangnet.com

 

[Wallyman]

First go here and it explains how to physically adjust it (scroll down to "2.) Defective TPS"):

Cranks OK, but No Start Checklist for Fuel Injected Mustangs

Cranks OK, but No Start Checklist for Fuel Injected 5.0 Mustangs model years 1986-1995 A word about this checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work...

stangnet.com

Then go here for the myth of as close to 0.99V as possible:

Mustang TPS Adjustment - 0.999999v not necessary

EDIT: This post applies to 86-93 5.0 Mustangs. Seems to be a common myth, so lets sticky a thread explaining how the TPS works. Jrichker has provided the basic TPS guideline to follow. But here's a snip of the A9L GUFB which is the programming logic. Pay attention to the part highlighted...

stangnet.com

I've read that checklist in a few threads, thank you.. I am following it as close as I can given I am not in a Mustang chassis, which is how I got to "mine is out of range". I don't see that heading tho, and searched the entire thread for "defective" to find it.

I wasn't saying 0.99 was an absolute must, just that it was my goal/the target. I know there is a range but also best to be away from the extremes if possible, I was reading getting above 1.25 (I believe it was 1.27xx on my fluke meter) and was able to pull codes last night after I replaced a corroded test connector. Codes I received:

23 - Throttle Position Sensor Out Of Self Test Range (O,CM,R)
31 - EGR Valve Position/Pressure Feedback EGR Circuit Below Minimum Voltage. 0.24 volts (O,CM,R)
67 - Park Neutral Position Switch Circuit Open; A/C On -Manual (O), Manual Lever Position Sensor Out Of Range/A/C On (CM,O), Clutch Switch Circuit Failure (CM)
81 - Secondary Air Diverter Circuit Failure (O)
82 - Secondary Air Bypass Circuit Failure (O)
84 - EGR Vacuum Regulator (EVR) Control Circuit Failure (O)
85 - CANP Circuit Failure (O)
87 - Primary Fuel Pump Circuit Failure (CM,O)

EGR and SMOG are removed, so all those codes make sense.
67 makes sense also as I don't have a clutch switch wired in right now.
85 canister purge codes makes sense as there isn't one.
87 I am not using the Ford fuel pump circuit, so that also makes sense (but could it impact cold start?)

I took a file to the mount holes and eventually elongated them enough to get it around 0.98. Didn't fix my cold start issue but idle now is 600 warmed up instead of 1100, so it did help. I need to recheck codes and see where I am, but the cold start persists. It took noticeably less attempts last night to get it to run after TPS adjustment, so perhaps that helped but not resolved... still requires starter fluid to fire when cold. Hot restarts are ok.

 

[Mustang5L5]

Ford code 87, the Mustang runs a single wire to the fuel pump relay to tell if it’s on/off and ties that into pin 19 I believe.

If that signal wire isn’t present, you’ll get the code 87.


The only code that I would be concerned with there would be the code 23 which indicates the TPS sensor is out of range. Erase the codes and verify it’s within 0.51-1.24 volts. Run the engine a couple of times and then dump codes again and see if it goes away.

 

[AeroCoupe]

So back to the fuel pump. You are not using the Ford fuel pump circuit? Can you provide some detail on how our are running the fuel pump? Are you turning the fuel pump on through a toggle switch prior to cranking? Pump needs to prime prior to cranking the engine. If you are priming it what pressure are you getting prior to starting?

 

[Wallyman]

So back to the fuel pump. You are not using the Ford fuel pump circuit? Can you provide some detail on how our are running the fuel pump? Are you turning the fuel pump on through a toggle switch prior to cranking? Pump needs to prime prior to cranking the engine. If you are priming it what pressure are you getting prior to starting?

Swap is in a Miata. Retained Miata fuel pump circuit completely, and (per the recommended approach) jumpered fuel pump to run constantly with key on. As soon as you hit run, it's on for the duration until you turn the car off. So yes, pump is on prior to crank and is fed from the stock Miata main relay that is powered during run and crank.

 

[Wallyman]

Ok, just checked and 23 code gone. the rest remain:

31 - EGR Valve Position/Pressure Feedback EGR Circuit Below Minimum Voltage. 0.24 volts (O,CM,R)
67 - Park Neutral Position Switch Circuit Open; A/C On -Manual (O), Manual Lever Position Sensor Out Of Range/A/C On (CM,O), Clutch Switch Circuit Failure (CM)
81 - Secondary Air Diverter Circuit Failure (O)
82 - Secondary Air Bypass Circuit Failure (O)
84 - EGR Vacuum Regulator (EVR) Control Circuit Failure (O)
85 - CANP Circuit Failure (O)
87 - Primary Fuel Pump Circuit Failure (CM,O)

Verified I am at 0.95v with KOEO. Cold crank no firing (without starter fluid). Ordered a fuel pressure gauge with -6AN adapter, will be here tomorrow. Verified fuel pump fires at KO to run, and I can hear the IAB clicking. I pulled and verified the IAB solenoid moves.

 

[Mustang5L5]

Only one I’d worry about is code 31. Are you running egr? If not, then don’t worry about.


Most of those are codes due to deleted smog stuff. Code 67 and 87 are nuisance codes and you can eliminate them if you care enough.

 

[Wallyman]

Only one I’d worry about is code 31. Are you running egr? If not, then don’t worry about.


Most of those are codes due to deleted smog stuff. Code 67 and 87 are nuisance codes and you can eliminate them if you care enough.

I believe all those codes are self-inflicted due to smog/egr removal, and that's fine.

Forgot the 5.0 has a test port on the rail, so I dug out the fuel pressure gauge and checked. 40 psi fuel pressure at prime, as expected. So that doesn't seem to be an issue for my cold start problem. Going to rig the noid light back up (had it on there previously) and confirm I am getting a prime squirt on the injectors...

Going to start a new thread about the cold start issue so maybe I get more hits and ideas on resolution.

 

[CAMTWO1070]

If you stated that youre using a 1994 TPS with an A9L..?..;- Theres your problem... a 1994 runs on the CBAZA strategy not the A9L..

The voltages dont match up// whether or not its a potentiometer it still has an internal grid that works differently

Heres A9L.. Notice how many settings there is for the TPS



vs CBAZA





Buy the right TPS and also Im pretty sure the 94TB is larger too and used a 70mm Mass Air Fow sensor to match..



Im pretty sure once you get the correct sensor the engine will start cold but will also run lean with a pretty fast idle..

Good Luck