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WRB Diesel
04-30-2008, 20:02
('94 burb) So I have only had the vehicle on the road now for about 1,000 miles and today I was stranded for ½ hr on the freeway before surging to an off ramp. I am having a hard time pinpointing the problem and wanted some other opinions before I drive an hour and a half to try and fix the vehicle on the side of the road. Here is the scenario:
I spent most of the day driving around the foothills looking for property to buy and places to cut firewood, I probably drove about 150 miles today in the process. The roads were paved but I did drive through a bit of snowy/slushy/muddy roads getting the vehicle fairly dirty. On the way home (luckily not 30 miles in the woods) as I was merging onto the freeway the vehicle began to buck and surge like I was stomping on and off the throttle and the tranny was downshifting into 1st or 2nd gear. I let off the throttle and things smoothed out and I continued on. However, about ½ mile further the vehicle began to accelerate without me touching the throttle to the point of the rpm’s reaching 5,000(runaway on own). I pulled over and shut the vehicle off. I sat there for about 5 minutes and tried to restart the vehicle, it would restart and jump from 2,000 to 4,000 and then quickly to 5,000. Killed it and sat for 10 minutes, made sure all connections were good and nothing had been dislodged on the forest roads. Upon restart the vehicle would instantly jump to 1800 and then die. Noticed during the restarts a slight bit of black smoke and some white smoke followed. Did this 5 to 10 times and same results. Sat in the vehicle for another 10-15 minutes and restarted; this time no problems so I quickly got off the freeway to an off ramp, maybe 1.5 mile down the road. Vehicle started to surge again, just for a half second or so the rpm would jump 1,000. There I parked the vehicle and sat for 10 minutes and then restarted again with no problems. I let the engine idle while I waited for my ride and after about 8 minutes engine started redlining on it’s own. Killed the engine and tried a few restarts again, on these last few restarts the black smoke on startup was much more noticeable and as the engine would surge black smoke would puff out in bursts. Vehicle now sits waiting for me to come back and try to fix or have it towed home for 500.00 dollars.
Things I noticed, FSD was cool to the touch, a little dirty but the connections were good(mounted on heatsink at back of bumper) The air filter seems to be very dirty for one only 1000 miles. NO SES light, not sure of any codes ‘til tomorrow when I can take the computer with. Any thoughts? FSD, TPS, Pedal Position, IP ? Assuming its FSD since with a little time and cooling things seem to go ok for a while. Do these things really crap out when not getting even overly WARM? Can’t wait until summer and things get hot. Newer IP, probably only 2 -3 thousand miles (5521), unknown age of FSD.

Sorry for the long entry, figured more details the better.

Thanks

Kennedy
05-01-2008, 06:36
I guess the simplest place to start is with a PMD/FSD. I've tried used ones and seen them run away. I've also known of guys changing EVERYTHING under the sun from PMD, APP module, ECM, etc chasing a more mild runaway/erratic throttle control only to be teh pump sticking internally in the end.

Robyn
05-01-2008, 07:14
I am with John 100% on this one.

The PMD can do this very thing. I was testing some usedc PMd's I got from the local IP rebuilder asd I got them basically for pennies with the promise that is they did not work to bring them back and exchange them.

Get a fresh Dtech PMD and plug in the little monster and see if the issue is resolved.

If this does not help you have other issues.

Now the best protocols suggests to check for any Codes before replacing everything under the hood.

Did you get a SES (MIL) light at any time during the incident??

If no mil light then the PMD may very well be the culprit.

The fuel solenoid in the IP is driven by very small electrical impulses from the ECM that are amplified by the PMD.
If the PMD fails in a particular way it can allow for a very near full fuel condition with no control.

This very scenario is why there is the shut off solenoid on the front of the IP.

Normally the shut off does not actually stop the engine but only assures that there cant be an uncontroled runaway with no way to stop it.

The fuel solenoid in the IP receives signals as well as sends them back to the ECM if the solenoid sticks due to a mechanical issue (wear or crud in the fuel) the return signal will usually be improper and a code will set.

If however the PMD goes BUZZZZZWHACK and there exists an improper power signal to the solenoid there can be a full power windup and no codes set.

See what happens with the PMD and keep us posted.

Best

Robyn

WRB Diesel
05-01-2008, 07:46
Thanks for the replies, I am heading out in a few minutes to retrieve the vehicle, plan on taking computer to check codes, I will order a new PMD today and let you know the status. Tell me why again do we have all these sensors, controls and electronics to make us go down the road?

Aryn

ToddMeister
05-01-2008, 09:24
Tell me why again do we have all these sensors, controls and electronics to make us go down the road?

Aryn


Three letters: EPA

Bnave95
05-01-2008, 10:12
If PMD has no effect go for the Crank pick up sensor.
When my sensor acted up I also had a code 19 though this did not keep the SES light to stay on.
With that issue I also would have the runaway on top of a pump that was not sure what stae of mind it had.:rolleyes: