Fuel Delivery/ TPS Sensor problems

[aball4620]

So I've used TRS forums for the last couple years on this truck and I've finally hit a place where I can't find the answers I need. My 88 2.9 with dual fuel tanks has had a ton of parts replaced over the last year including new upgraded heads. I keep getting code 63 - TPS signal voltage too low. Problem is that replacing the TPS hasn't fixed the issue. The truck starts right up, idles high while warming up, then settles down to about 800 with periodic flutters where it almost dies (or sometimes does). When I try to rev it in neutral or in gear it will not get above 1800 rpm. This is a dual tank ranger with an almost brand new high pressure pump and filter. It is acting like it is starving for fuel, but it does this on both tanks. FPR is bone dry and brand new. The tank selector was recently replaced because it had clogged up and was creating a ton of back pressure in the return line. Fuel pressure sits right at 30 psi which is on the low end but it is stable. Vacuum stays right at 18 and drops as expected with hitting the accelerator. Everything else on the harness - o2 sensor, air temp sensor, coolant temp sensor, IAC, and injectors are all new or reman-ed (injectors), and some of those have periodically thrown codes as well, but the most recent round it is just 63.

Does the harness that runs the TPS ever go bad? How about the computer? The pin for the TPS looks fine or at least not burned up. Happy to give a run down of all the work done and reasons for it if anyone has questions. I'm completely stumped on this one!

 

[rusty ol ranger]

Is the TPS adjusted properly? Should be under 1v at idle up to around 5v at WOT.

Also, yes wiring can go bad to it. I doubt its ECM if its the only issue you are having,

 

[aball4620]

Is the TPS adjusted properly? Should be under 1v at idle up to around 5v at WOT.

Also, yes wiring can go bad to it. I doubt its ECM if its the only issue you are having,

I haven't tested the sensor yet. As it is a 30 year old truck I've happily replaced the sensors when I discover they are acting up. I have three sensors right now and they all give the same result. It seems this style isn't adjustable.... or do you mean with respect to the screw stop on the throttle?

 

[rusty ol ranger]

I haven't tested the sensor yet. As it is a 30 year old truck I've happily replaced the sensors when I discover they are acting up. I have three sensors right now and they all give the same result. It seems this style isn't adjustable.... or do you mean with respect to the screw stop on the throttle?

Yes with the screw stop. @adsm08 or @PetroleumJunkie412 is better with the electronics side then i am

 

[aball4620]

Yes with the screw stop. @adsm08 or @PetroleumJunkie412 is better with the electronics side then i am

I did play with the idle set screw a bit wondering if that might be the issue. I backed it off and tightened it a full turn and it didn't change the symptoms in either direction. I did adjust the idle speed.... so before when it would periodically shudder it would drop about 300 rpm and die. I set it slightly higher so now it will still periodically shudder and drop 300 but it doesn't die. I've also tried two different throttle bodies with the exact same results - one is the stock small bore and the other is the larger (54mm I think....) from an 86 or 87. They use the same TPS.

To give a little more background - I replaced the rotted out relay harness with fresh wires and relays. When I initially bought the truck I had some insulation that rotted off the fuel pump relay and if jiggled in the right way would short. Some liquid electrical tape got me through for a long time but always with the intention of eventually replacing. The long term symptom with this truck was a little wispy white smoke and the smell of fuel at the tailpipe, along with horrendous mileage. Otherwise zero performance issues. When I replaced the relay harness ends, suddenly no more wispy white smoke or smell of fuel. I also double checked all of the fusible links at that time including the one behind the coil. Everything had continuity.

 

[bobbywalter]

I slot the holes on the tps for fine tuning adjustment.

Are you saying at pin 47 on the eec, your getting .6 or so volts throttle closed...and 4.5 to 5 volts at wide open?


if that is the case the pcm is bad or the pin on the board is bad.

 

[aball4620]

I slot the holes on the tps for fine tuning adjustment.

Are you saying at pin 47 on the eec, your getting .6 or so volts throttle closed...and 4.5 to 5 volts at wide open?


if that is the case the pcm is bad or the pin on the board is bad.

I’ll have to run the multimeter over the eec. I haven’t tested it yet, just meant that there was no visible damage from overheating or water. Would the WOT readings at pin 47 need to be done in KOEO or KOER?

If it is a bad TPS would lack of fine tuning be causing such a dramatic issue? The adjustment on the TPS and idle adjustment weren’t touched during the head install. And I’ve swapped out three sensors with no change in symptoms. It’s making me think the issue is in the wiring somewhere.

As a side question, having two fuel tanks affords me some confidence that my low pressure pump isn’t bad given that I have two. The chances of them failing simultaneously seem slim. But is the wiring shared? This was part of my reasoning for finally addressing the relay harness. Is there a hidden fusible link somewhere that feeds both in tank pumps but not the high pressure pump?

 

[bobbywalter]

Fine tuning in this case is a non issue....likely a connection or wire issue.


Dual tank power splits off the switch on the trucks I worked on down stream of the inertia switch and the high pressure pump.

The gauge splits off of the selector valve.


I always check for power at the tps...and then go to the signal pin to know the wiring is ok. If the signal is not making it to the PCM it is likely a wire obviously...as you expect.

 

[bobbywalter]

Key on engine off testing...should be fine..

 

[franklin2]

This is what the guy in the book says about code 63.

Disconnect the harness connector at the TPS. Place a jumper wire between the 5v wire (orange wire) and the signal wire (darkgreen/lightgreen) Then repeat the key on engine off code test on the engine again. If you get the code again, make sure you have 5v on the orange wire. If you do have 5v on the orange wire and are still getting the code with the jumper in the plug, there is something wrong with the darkgreen/lightgreen wire to the computer.

With those wires jumped, you should get a code 53, TPS voltage high.

 

[aball4620]

This is what the guy in the book says about code 63.

Disconnect the harness connector at the TPS. Place a jumper wire between the 5v wire (orange wire) and the signal wire (darkgreen/lightgreen) Then repeat the key on engine off code test on the engine again. If you get the code again, make sure you have 5v on the orange wire. If you do have 5v on the orange wire and are still getting the code with the jumper in the plug, there is something wrong with the darkgreen/lightgreen wire to the computer.

With those wires jumped, you should get a code 53, TPS voltage high.

Great idea and an easier process of elimination. I assume no real chance of frying anything in the eec trying to elicit code 53?

 

[aball4620]

Fine tuning in this case is a non issue....likely a connection or wire issue.


Dual tank power splits off the switch on the trucks I worked on down stream of the inertia switch and the high pressure pump.

The gauge splits off of the selector valve.


I always check for power at the tps...and then go to the signal pin to know the wiring is ok. If the signal is not making it to the PCM it is likely a wire obviously...as you expect.

So the inertia switch was bypassed by the PO. I hadn’t considered checking that circuit but will again. He just used a wire nut in the foot well. It is only two wires and best I can tell both run from the fuel pump relay, but I haven’t checked for continuity. My undetanding is that the switch will cut power to the relay, thus cutting all pump power. Does power run first to the high pressure and then split to the low pressure or do they run independently from the relay?

 

[franklin2]

Great idea and an easier process of elimination. I assume no real chance of frying anything in the eec trying to elicit code 53?

Won't hurt it.

 

[aball4620]

Alright so after this sitting for a week I apparently have no codes now. I did check the function of the TPS and has a nice smooth curve. Sits at 0.79 when idling and tops at 4.5 WOT. Now the engine wants to rev but acts like it is starving for fuel. Hesitates and shakes when trying to rev. Does still have a little shudder now and then at idle where it drops about 200 rpm then catches itself. While warming up it was a super rough idle and constantly tried to die but never did. Looks like I'm working on checking for power to the in take pumps, unless anyone has another direction I should go. I don't have a fuel gauge on hand to check for pressure while revving, but can go rent one of from the LPS if that would be useful info.

 

[PetroleumJunkie412]

Should be 0.98-1.01 at idle.