This is on a 1994 6.5 TD k3500. Was driving home today and at about 20mph it revved up with out stepping on gas. Stopped when I step on brake. Scared the crap out of me I was driving in heavy traffic. Does any one know what I should fix to stop this? Parking it until I remedy this. Not worth the risk. Any one have a diagram of the pedal assembly? Thanks.
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Gas pedal is sending gas to engine with out pressing it.
- Thread starter Blue
- Start date
Will L.
Well-Known Member
Check for dtc's . If nothing -Swap in your spare pmd.
NVW
Well-Known Member
PMD and IP are 2 causes of this.
Welcome to TTS.
I have Flight Systems and Stanadyne PMDs in stock LMK if I can help.
I have Flight Systems and Stanadyne PMDs in stock LMK if I can help.
JayTheCPA
Well-Known Member
Mine did this. IP replacement cured it. ECM also had stored a code but did not turn on the light.
Less expensive test is to swap with a known good PMD and see what happens.
Also, least expensive test is the 'idle test': slowly cycle from idle to 2,000 RPM, hold for a second or two, slowly return to idle, and repeat 10 (Yes, 10) times. If the RPM's do not evenly track with the throttle or they go run-away, chances are it is the IP.
Less expensive test is to swap with a known good PMD and see what happens.
Also, least expensive test is the 'idle test': slowly cycle from idle to 2,000 RPM, hold for a second or two, slowly return to idle, and repeat 10 (Yes, 10) times. If the RPM's do not evenly track with the throttle or they go run-away, chances are it is the IP.
- Staff
- #6
This is known as fish bite if you want to search old posts on it. First thing is to make sure your lift pump is working as a change in supply pressure to the IP will do it. Most of the time it seems to be a bad PMD, it can also be a bad fuel armeture in the injection pump(which requires pump replacement), but then theres the UBER rare case like mine where it was the ECM. Many have argued and said an ECM wouldn't do it, but my ECM got put into another truck and it started doing it. The best thing you can do is to do all the 6.5 checks on the checklist, and go from there.
In addition to the above:
Do you leave the cruise control in the "on" position? Sounds like cruise may have been bumped on including bad wires to the multi function control on the turn signal. The brake of course cancels the 'resume' speed request.
The APP accelerator pedal is a 3 pot sensor and not where you need to start. It's failure will turn on Service Throttle Soon and/or SES lights.
Do you leave the cruise control in the "on" position? Sounds like cruise may have been bumped on including bad wires to the multi function control on the turn signal. The brake of course cancels the 'resume' speed request.
The APP accelerator pedal is a 3 pot sensor and not where you need to start. It's failure will turn on Service Throttle Soon and/or SES lights.
Ok, did not drive truck for a few days. Started right up ran fine until it reached temperature. Then it started fish biting. I am assuming, it's the pmd considering it started when reached operating temp. If it was lift pump would it fish bite upon start up or not start at all? I wanted to relocate pmd anyways, this looks like it is forcing my hand. Thoughts? How can I test ECM?
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Sent from my iPhone using Tapatalk
- Staff
- #10
Check your lift pump when it does it. Not accelerating sounds like it's running out of fuel. When it does it, stop, and open the drain valve for the fuel filter and see if it stalls or you have a good stream of fuel.
Relocated pmd this eliminated fish bite and other acceleration issues. Actually runs a lot better even before noticeable issues. What exactly does the pmd do? I understand it helps control the ip, is it doing this by taking atmosphere readings thus controlling fuel air mixture?
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Sent from my iPhone using Tapatalk
- Staff
- #13
Nope, the Camshaft spins the IP, the optic sensor in IP reads the rotation, sends that signal to ECM which takes that information, along with atmospheric pressure, temp, and the input from your foot thru the APP. It then computes which timing and fuel curves are optimum for achieving what your foot is asking for, and sends signals to PMD which energizes the fuel solenoid in the IP so that fu is injected.
if the PMD craps out, you get surging, changed timing, erratic injection events, or nothing.
if the PMD craps out, you get surging, changed timing, erratic injection events, or nothing.
- Staff
- #14
The PMD or FSD is the driver that energizes the fuel solenoid. The DS series of injection pumps replaced the manual cable with an electronic solenoid to actuate the throttle control. The PMD is what sends power to the solenoid to control thee throttle of the pump basically. The solenoid in the pump requires more current than ECM's of the day could supply, so a seperate driver(AKA PMD/FSD) was used to supply the current, and the ECM sends the trigger signal to the driver to in turn activate the solenoid and how far it opens.