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Why when i touch the gas pedal it accelerates like I put my foot to the floor. when cruising in 5th gear, it fells like it is surging and slowly picking up speed. If in neutral and stopped, I can just touch the pedal to raise the idle and it revs to the moon... driving me nuts....
That sounds like the symptoms a a failing flight systems PMD provided you have a 94 or newer truck.
Is there any unusual smoke issues when it is surging and acting up?
The other possibility is that your IP is on the way out,PMD is the cheaper alternative when diagnosing and it is never a bad investment to have a spare.
Its a 1995. The pmd is a stanadyne. would the electric gas pedal give me this symptom?
DmaxMaverick
06-12-2012, 21:36
Its a 1995. The pmd is a stanadyne. would the electric gas pedal give me this symptom?
No. By the time the APP signal(s) are that bad, it will set the STS lamp (Service Throttle Soon) and you'd have no throttle. It has 3 redundant circuits. Lose one and the lamp comes on. Lose 2, the lamp is on, and you are in limp mode (limited engine RPM). Lose 3 and you have no throttle, if it starts/continues at all. As Racer said, sounds like PMD or pump.
I have an old pmd that cuts off when it heats up, but it works for a test. I'll give it a shot and let you know.
Thanks
Ok, while playing with truck I pulled some codes. #1) 24 -speed sensor low, #2) 44,45 - EGR ( where is the EGR on this motor. #3) code 87, High Ratio ( what the heck is high ratio ).
DmaxMaverick
06-13-2012, 09:28
You have several transmission codes that may or may not be related to one another. I suggest checking the tranny connector and harness for open/poor connections and/or damaged wires.
As always, any time you get unrelated codes (or for any or no reason at all), check/clean all battery connections, and pay special attention to the grounds. The 3 key grounds are: Battery to frame; battery to block; passenger side rear head to firewall. There are others, but the head/firewall ground is a usual suspect, and is essential to PCM/emissions system operation. Check/clean all you find.
You need to confirm that you actually have EGR, and/or if you are supposed to have EGR. If the 8th digit of the VIN is "S", you are supposed to have it. If it's "F", no EGR. If you have a vacuum actuator pod on top of the intake manifold, you actually have EGR. Follow the vacuum line to the EGR solenoid, which is where the fault is occurring. If you wish to keep the EGR system working, try soaking the solenoid (through the vacuum nipples) with WD40, shake dry. It may loosen up and begin working. Check all the vacuum lines for damage, cracks, loose connections or open connectors, and verify your vacuum pump is producing at least 20" Hg vacuum, ideally 22-24" (up to 26-27" is OK). If you lose vacuum, the solenoid will fault. You may also have issues with black smoke and/or low power under higher engine loads, depending on the vacuum pump performance. The vacuum system is necessary for wastegate control, unless it's been converted to mechanical (Turbo Master).
Ok, I have a "F" Vin. and there's no EGR valve that i can find. Also i read in a different post about air bubbles in the return line. So i hooked up a clear line from the rail to the line going back under the manifold, and sure enough i see bubbles. they pass thru and then wait 5 or 6 seconds, and a hole bunch more passes, wait and then more. but would air bubbles make the RPMs sky rocket when i just touch the peddle or is this just some more issues that this truck has...
By the way, thanks for all the input your giving me. I really appreciate it.
The clear line that needs to be installed for air in fuel check must be connected to the IP fuel return fitting at the front of the IP and is intended to replace the line that is already there.
You have put the clear line in the wrong place and will be of little value in that location.
Air in the fuel will confuse the Optical sensor and cause a great number of strange problems.
DmaxMaverick
06-13-2012, 11:51
Yep. You installed the clear line in the wrong place. More accurately, you didn't install it where we would most commonly install it. Actually, your faux pas is more telling than if you had installed it correctly. That much air running through the injector return line indicates significant air passing through the IP, injector lines, and the injectors. This, in itself, can and will cause retarded timing to the point throttle response is incontrollable. Air passing through the pump doesn't always indicate the air is actually being passed through to the injectors.
It also seems you have a PCM issue. Perhaps it was replaced with the wrong model (VIN "S" PCM). You shouldn't be seeing EGR codes, at all, if it's correct. Even if the PCM failed, you still wouldn't see them.
Start by checking lift pump operation. Correct it, then find your leak.
I put the clear line on there first but had no air bubbles, and then did than other one and saw the bubbles. And yes, My throttle response is uncontrollable. My lift pump is pumping, cant see a leak, could it be the feed line under the manifold that feeds the IP. the IP sucks the fuel from the filter, correct? so there will be minimal fuel in area, Am I on the right track?
No air bubbles in the fuel return from the IP means no air in the fuel.
Seeing bubbles where the line is currently does not mean air but it des mean that the fuel bypassing the injectors is not that significant-an empty space between fuel pulses is normal and extra fuel not being used during injection is coming out in pulses with nothing between pulses.
The LP pressurizes the fuel all the way past the filter to the IP,the IP is never intended to suck fuel on it's own but can if conditions are right.
A great many people also get false codes from cheap code readers on these trucks,while the code displayed may be a valid code the readers do not always relay the correct code #'s.
Have a quality scanner extract the codes.
Would you mind telling us what year make and model the truck is?
The truck is a 1995 GMC 3500HD, 4 wheel disc brakes with a Dana 80 rear. i love this truck, but every time i turn around its something else. lol. but would the optic eye be the reason my uncontrollable throttle response. or maybe the PMD (fuel driver). i have an old PMD that when hot cuts off - Stanadyne # 34583. Dose the PMD have any control on the throttle.
Sure the PMD could be faulty-so could the IP.
Stanadyne runaway PMD's are rare but do happen.
Since you don't have air in the fuel the OS is of little consequence
greatwhite
06-13-2012, 15:27
The PCM controls the pmd which controls the fuel solenoid which determines timing and quantity.
If the pmd is going, it's entirely possible that is your problem.
Failing pmd's can cause some weird behavior. I often wish they would just completely fail when they go rather than the progressive breakdown and weird faults they sometimes cause. Would make troubleshooting much easier.
If you have a known good one, try slaving it in to see if anything changes/improves.
The optical sensor can cause a sensitive throttle if someone has done the "optic bump" on it. But, if it was running good before and you haven't messed with the sensor it's unlikely this is the cause.
The programming for an HD has the egr codes in it, but gm has the error reporting turned off in the calibration. That they would show up is odd. I'm betting on a generic scanner reading the codes and trying to report generic obd codes for gm specific codes.
Are you using a scanner or are you getting the flash out codes? Since its a 95 you should be obdI, so you can get the IND codes without a scanner. I'd clear the codes and see what returns using the "flash out" method.
Good luck.
Well, the other PMD did the same the same thing. How many parts are associated with the IP. OPT sensor, shut off solenoid, PMD, and stepper motor. What dose the stepper motor do and is that the thing to the left of the IP while looking at it from front of truck. also, is code 87 for auto tranns, because i have a stick...
Thanks everyone, got it running better then ever. Put an injector pump in, did a timing reset, and it works great. must of had issues all along, because its got much more power and it runs cooler. not sure why its running cooler, but it does.
Having the timing set properly helps make it run cooler,late timing makes a lot more heat.
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