I would try checking the voltage on the TPS. Connect your voltmeter and with the KOEO and check voltage as you move the throttle toward WOT. You should go from about 1v to about 5v. If you see any sudden drops then your TPS is bad.
Autolites I put in are stock gap (.052 I think). The platinums that were in it were the double tips - couldn't check the gap but didn't look worn.
The TPS was around 1 at idle and 5 at WOT but I did it while running. Didn't even think of testing it KOEO!! That would allow me to take my time and check for drops in between!
Thought I’d dig this thread back out and re-run it. I’ve seen this problem listed before here and in other threads, maybe worded a little differently, but essentially the same problem. Have never seen any solutions listed though….
The only thing I can think of at this point is that I need a new computer. I’ve driven the car for a couple months now and the car works fine in every way, except when I have it floored (wide open throttle). I can consistently run the car up and down to and from 5000 RPM and it will hold at 5000 RPM as long as I want with no issues at part throttle. For that reason, it just can’t be the normal wires, fuel pump, fuel flow, injectors plugs, plug gap, that type of problem. It has to be a computer or sensor signal to the computer problem. The car runs fine, as long as it’s not floored. When it’s floored it bogs and will slow down and keep slowing down as long as I keep it floored. Drop back to part throttle, and it picks right back up.
Other than replacing the TPS which tests ok or the computer which really should have no way of being able to change its own settings (both of which I hate to just throw money at and buy for the sake of change), at this point I’m still at a loss for a solution.
Anyone had this problem and an explanation as to what solved it?
Picked up a computer and swapped it out, no help. Guess I'll look for a used MAF (new remans appear to run $90.00 to $120.00) and try switching that next.
I reskimmed this - maybe you can do a quick bullet-list recap of what's up and what's been tested/replaced (if not all listed in this thread already) ?
I doubt it's the MAF. You can watch it's voltage in real time if you desire. If you have a buddy with a MAF, just swap it (the MAF and MAS, not just the sensor) for twenty minutes of testing.
Can you tap into the TPS wiring at the puter and watch the values in real time? I need to double check but I believe that the T4 processor sees WOT at ~ 2.7 volts over the baseline, like fox TPS's do (read: the computer assumes WOT at ~3.7 TPS volts).
Do you have a means of watching PIDs? If so, you can watch your TPS and a fair number of other parameters in real time.
Cleaned my MAF twice, nothing. Bought a used one, still the same problem.
The original MAF in the car tested at 3.7K ohms and the used one I got was 4.2K ohms. In other words , neither tested as open or a broken circuit. Backprobing the connector, the original in the car was .69 volts at idle and approx 1.9 volts at a high rev which appear to be ok numbers per my Haynes book which shows .2 to1.5 volts at idle with it increasing to 2.0 volts at 60 MPH. That sound right? Maybe the used one is bad too...
I've had two local mechanics test drive the car and they both said it lays down like it's a fuel issue not electrical. One swore it was the MAF. After switching to the replacement computer with no luck my money was on the MAF. Now I'm totally lost as to where to go next...
Replacement/check recap:
Car driven approx 2500 miles in the last 2 years, all replacements parts have less than 2000 miles on them. K&N filter, headers, Flowmaster cat-back are only intake/exhaust mods. No fault codes showing up on computer.
MSD 8MM Heli-Core wires, cap, and rotor replaced by previous owner. Have approx 8-10,000 miles on them with no apparent shorts. Have checked and cleaned cap, rotor,and distributor internals
When purchased car had intermittent starting issue so replaced:
New IAC - Idle Air Control Valve
New Ignition Coil
New ICM -Ignition Control Module
Added fuel gauge on rail, fuel pressure regulator increased PSI w/o vacuum but still decided to replace fuel pump. Everyone swore it was the fuel pump.
New Fuel Pump - standard flow Carter
New Fuel filter
New Ignition switch. Ignition switch fixed it!
Started having WOT throttle issue last summer
New Spark plugs (Motorcraft with factory .052 gap)
New Air filter - changed K&N out for stock Fram paper filter and cleaned MAF twice
Pulled distributor top apart, clean and no apparent loose/broken internals
TPS- Throttle position sensor checked ok, was .96 volt at idle to 4.69 at WOT
ACT - Air Charge Temp sensor is 60.1K ohm @ 49°F (within spec)
ECT - Engine Coolant Temp 4.67K ohm @ 170°F, 23K ohm @ 87°F (within spec)
Swapped computer, no change
Swapped MAF, no change. Original MAF tested 3.7K ohms, .69 volt @ idle, approx 1.9 volt at high RPM
Think that's everything.....
The only thing left that you haven't changed is the pip sensor in the distributor. It looks like you have already replaced the TFI, which is the first thing I would look at.
Remove the coil wire and test the resistance.: It should be less than 100 ohms for the type of wiring you are using. Check the spark plug wires too. The resistance should be the same for them.
Follow-up on the MAF:
Does anyone have any more of a detailed spec for the what ranges in terms of volts or ohms for the MAF should be for a 94-95 MAF P/N F2VF-12B579-A2A (also known as F2VF-12B579-AA).
From all the sources I've found, the F2VF-12B579-AA is the P/N listed for most all 92-95 5.0 Fords (including the Mustang) so I assume that the -A2A and -AA are the same.
If anyone feels like offering up their ohms and voltages on their MAF for a comparison, probe the black (-) and tan/blue (+) wires on the connector (or terminals B- & C+ on the MAF connector).
Thanks
When you say TFI, do you mean the TFI (thick film ignition) module that was used on the distributor? Is what you're calling the TFI essentially the same as the ICM (ignition control module) that I replaced that's under the air cleaner? I believe the TFI was used on the 84-94 Mustangs but Ford got sued and they switched it to the ICM. Any idea if that's the case? Just wondered, is this a terminology difference or is there another part I need to be looking for! Thanks
You're correct - the TFI was reclo'd in '94 to a heat sink on your passenger fender. When people PM me to ask something, they often refer to the ICM, so it must be common nomenclature somewhere. I still call it a remote-mounted TFI module.
I didnt get around to testing the MAF stuff for ya, but I'll offer what I can. In the past, I have farted around with the signal terminal and the MAF return terminal.
Going from memory (take this with a grain of moutain): My MAF signal wire had .96 volts at idle (800 RPM) and would go up to almost 2 volts if I stabbed the throttle to about 2000 RPM (this was all done static - no load on the motor).
*I think* the return terminal showed 0.10 volts at all times during my testing. I never got around to seeing what it should read.
BTW, this was done on the '94 with an F2VF MAS.
EDIT: I seem to recall Grady and the self-tuning crowd saying that an idle MAF reading of ~1 volt was where they ended up. Now I don't pretend to understand MAF's that much (how there can be such a wide range of acceptable idle readings in the repair manual - that would be a huge range of airflow differences). However, the fact that at 60 MPH you seem to be right-on suggests that perhaps the MAS is decent at higher speeds.
This was an old thread of mine but I thought I'd come back so anyone looking at it would know what the final resolution was.....
Well I'm glad to announce that after almost an entire year of jackin' around with this thing I finally found the problem.
LESSON OF THE DAY: Don't assume that just because you've got a new part that there can't be anything wrong with it....
This solution to this is going to sound so simple ...... I found that my new fuel pump was defective!
I dropped the tank today, took the pump back to Pep Boys and swapped it for a new one (Carter brand standard OEM style).
It's running great!
Thanks for everyones suggestions over the past year!
My suggestion for those of you having a problem similar to mine, for a quick easy test, pull the schraeder valve out of the rail test port, clamp on a piece of 4-5ft hose, and attach a PSI gauge at the other end and then tape the PSI gauge to your windshield. The PSIs may look ok at idle, but you you need to test the pressure at WOT and see if that's the problem. (Remember this is only a temporary test set-up).
This is at least the third time now in my 30+ years playing on cars that I've been caught like this by defective new parts. Should know better by now, use common sense in trouble shooting and never assume new always means it actually works...