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Suddenly no throttle

dbrannon79

dbrannon79

I'm getting there!
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Location
Seguin, TX
Good morning guys,

I need a little help trying to figure out what happened this morning on the way to work. My 95 pickup has been running fine lately, but this morning when I pulled into my work place and stopped at the guard house I noticed that all of a sudden I had no throttle as if the truck would only idle. I tried to feather the pedal and it would suddenly just go and drove normally again. as I drove through to get to the parking lot it would do the same thing at every stop, had to feather or press further down on the pedal for the truck to pickup and go. although when it did, it would act like I romped on the pedal and try to take off. it idles fine and there's no misfire. it's almost as if the little potentiometer on the gas pedal just took a dump! I talked to a buddy of mine here at work and he said chances are that my injector pump is the problem! I would hate to think this but it does have 275K miles on it. I know it does have an underling problem I just haven't tried to address yet, but after it sits over night or for several hours it usually doesn't start until the second try and when it does it throws a large puff of diesel smoke for a second or two. I know the glow plugs are working since I recently replaced them and tested their operation. are there any things I can do to verify if my injector pump is failing!

edit: something I forgot to mention is that I also noticed the other day while trying to warm it up a little faster is that it's extremely hard to idle it up to 1000 or 1200 rpm and hold it there with the pedal. a very light press of the pedal and the rpm just keeps climbing. it's like it has a very touchy pedal! if that helps anything.
 
I've had the APP do something similar but it was cold, below zero, and after it warmed up it was fine. If it does it all the time then I'd lean towards the IP having issues. Try disconnecting the temp sensor in the coolant crossover next time you start it cold.
 
ak diesel driver said:
I've had the APP do something similar but it was cold, below zero, and after it warmed up it was fine. If it does it all the time then I'd lean towards the IP having issues. Try disconnecting the temp sensor in the coolant crossover next time you start it cold.
Click to expand...

well I'll find out when I drive it home this afternoon. when it did this the truck was already warmed up as I was just pulling into my work. the outside temp was about 40 deg this morning.

Should I disconnect the temp sensor before I start it up when I leave or wait and see what it does on the trip home? what should I look or listen for when the sensor is disconnected?

I'm not sure if the rpm climbing or the touchy pedal that I experienced the other day is related to what happened this morning but this was the first time for the "no throttle" while trying to drive into my work from the entrance to the parking lot! can the throttle sensor thats on the pedal just go out like that? I'm not sure what it actuates in the IP that throttles it up when driving. I know on gassers there is a stepper motor on the engine that controls a butterfly for air flow, but on the 6.5 I would assume this is built in the IP for fuel flow or something in the PMD (which is relocated over by the brake master cylinder.
 
If it were low trans fluid or slipping clutch if manual trans, the engine rpm would raise but truck not move.

The little potentiometer/ throttle pedal is named the APP by the way.

When is the last time you removed, cleaned, and reinstalled grounds? All engine grounds, battery grounds, ecm ground, pmd ground.

“washing” the APP with electric contact cleaner (a can is about $8 for crc brand, $35 for the best stuff out there), but crc should be fine for this.

Do you have a spare pmd mounted? If so, plug it in. Faulty pmd can cause all kinds of wacky stuff like this.
I suggest moving that pmd out of the engine bay. When you shut off engine and the fan stops blowing air, the heat under hood still soaks in. Down on the back side of the front bumper is a popular location that works.
 
snarl95 said:
Low on trans fluid?
Click to expand...

no I had just checked the fluids on Sunday. it was acting like the RPM wouldn't increase when I stepped on the gas pedal. I basically crawled into the parking lot while in drive and just ideling until the truck realized I was pressing the gas pedal harder until the RPM ramped up! I was feathering the pedal because I didn't want to take off like a bat and crash lol
 
Will L. said:
You can disconnect before you start it to drive home. Wont hurt. 160f is considered warm iirc
Click to expand...

what should I look for or listen for with it disconnected or should I ask how should it act? I am assuming that if the throttle pedal works fine with it disconnected I am looking at a IP problem?

on the grounds, I have done the battery grounds by not any others. not sure where they are located.

I do have a spare PMD at the house. I removed the one on the pump and re-mounted it.
 
I also may connect the GMTD scan tonight and see if it shows anything on the throttle. I think it should let me see the data on it with the free version.
 
1995 and the APP: what a PIA!

First check for codes. Next any codes dealing with the APP are suspect for one reason: if you key off and then key back on within 30 seconds the ECM hasn't fully powered off. The SES and STS bulb check will be random instead of both on. Further it will set a ghost code for the damn APP.

There are 3 variable resistors, potentiometers, in the APP. If they disagree the STS light should come on. You can watch the voltages change in GMTD. Further you can watch the voltages change after key off for about 30 seconds... Here is where the ghost code sets as the caps finally drain empty.

That said you should check grounds as @Will L. said. You should make sure there is a clear return line on the IP and no foam or bubbles. Fuel gelling is a possibility if it's exceptionally, unusually, cold where you are at. IR gun the FFM and see if it's hotter than the incoming fuel as the fuel heater could be dead. The tank sock will still screw with you and gelling.

Do you have a spare PMD on a heatsink you can try? :facepalm: Word: do you leave your spare tire at the house too? We give you credit for having one, but, when you need it...

The APP does fail and so does the ECM. However you have to be very careful troubleshooting them as new parts for those two items may not be your problem.

Can you hold a steady 1200 RPM in park? IP test I forget the details of.

Last don't be afraid to call the hook and get your ride home. (Cell phone co, ins, AAA: you may already have the hook paid for.) Some PMD failures like to go WOT on you at random. Have a plan if this happens. I prefer to drop it in neutral and use the last of the engine life for PS and PB before going key off. This plan saves one from having to make it up in a panic.
 
Most common ground fail points are battery puck that 2 cables connected together. The battery cable to engine.
Driver side rear of engine has a few connect by the transmission dipstick mount.
 
@WarWagon ya got me on the Spare at the house lol. I will check codes and the data from the APP and see what I can get. as for holding it steady at 1200 in park, that's what I was saying is extremely hard to do. just pressing a tiny bit on the pedal will send the RPM steadily climbing up and up.

@Will L. thanks for reminding me, I got rid if the FFM a back in the fall when I had discovered a fuel leak in the valley under the intake. all the lines were rotted and the bottom of the FFM was deteriorated. I had installed a remote mount fuel filter on the firewall since I figured south Texas never gets that cold! also installed a new oil pressure sensor and wired in a relay system for the LP that also helps prime when the glow plugs are on. I saved the FFM for later, but I do remember messing with all the wireing back around the firewall and also when I replaced the flywheel around that time too. I'll have to get in there and double check the grounds
 
Ok just made it home. I unplugged the temp sensor on the crossover pipe and fired her up. The truck started easily and with less smoke that it usually throws! I noticed the rpm was at 900. Just under a grand on the gauge. Drove out of my work just fine and up to the gas station down the road. Engine light came on after a bit with the sensor disconnected but that’s to be expected. While I was at the gas station I shut it off and reconnected the sensor. It started normal, rpm back to 600 idling and the APP hadn’t given me any issues since this morning. Took off for the house and made it with no issues.
While sitting in the driveway parked. I tried to hold the RPM at 1200 with the pedal and it was near impossible. The slightest press sent the RPM to 2k and when letting off ever so slightly the engine webs straight back to idle speed. I even tried it disconnecting the sensor again but still the same thing up to 2k and back to idle. I can get it to 1200 but it takes minuscule movements of the pedal and I can’t even hold it there long, it’ll start to climb to 2k again!! I’ll pull the codes in a little while but is this an indication of the APP going bad?
 
Usually a sign of ip worn out. Don’t plan on rebuilding it, get a new one. If you plan on keeping the truck, kinda better off his hit now because prices are gonna be shooting up more as they are getting hard to get new.
Include a fuel pressure gauge with the install and consider a really good water separator to protect the investment.
Obviously keep putting additive in with the fuel.

The other option is if you ever thought of doing a db2 swap- that would be the time. Again, only want to buy new.

Make sure it is reputable place not online where you get it.
 
Just read the codes...
15 - ECT ( because I disconnected it )
65 - APP 3 circuit range fault
78 - Wastgate solenoid fault ( I have a spring on the turbo Light turns on when I hit 70 mph )

Here are some screenshots from GMTD scan
Codes at Idle
1610496463334.png1610496510790.png
with pedal slightly pressed - Both screenshots with same RPM
1610496566400.png1610496603707.png
still slightly pressed but let off just a hair ... and engine off pedal pressed to floor
1610496940276.png1610496649112.png
 
Scowering the internet and can't seem to find anything on code 65 and what to test or check but I did find this youtube video that is almost exactly what mine is doing except for the surging. aside from the incident with no throttle this morning.

not sure if I can post the youtube link but if it's against the rules please let me know
 
JMJNet said:
This one comes from DP:
www.dieselplace.com

Injection Pump my AZZ

www.dieselplace.com www.dieselplace.com

Hopefully, it is ok to cross post from another forum.
I cannot find it here.
Click to expand...

this sounds almost like what is going on with my truck, except for the bucking. I looked up on Advanced auto's web site and they don't list an APP for it. only a TPS but I'm not sure there the same thing. would anyone have a AC Delco part number that I can cross reference to them or possibly on Amazon? I'd rather spend $$ on this first before dropping the bucks on an IP !!
 
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