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94 C2500 LD, reved high for a second...

vstech

vstech

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Location
Charlotte, NC
I was parking the truck in a tight lot, and the idle shot up for a split second... startled me.
it's a black stanadyne PMD on a 6' extension mounted behind the turn signal...
it only did it once, and only for a second. my foot was already on the brake, so no issues, but I could see how that would wreck the truck!!!
any ideas?
 
Mine was an ECM when it started doing this. Tried another PMD with no change, swapped in new ECM and never happened again. Also it can be an early sign of the fuel solenoid armeture failing, and bad grounds can wreak havoc with this issue as well.
 
My 95 did this and it was PMD related. Roasted the tires at a stop light with a D Tech on the upper intake. Ive since remounted and havent had an issue in 2yrs with the new grey standyne and cable from leroy.

Check PMD connections and grounds. maybe make sure the solenoids inside the pmd havent vibrated loose.
 
tanman_2006 said:
My 95 did this and it was PMD related. Roasted the tires at a stop light with a D Tech on the upper intake. Ive since remounted and havent had an issue in 2yrs with the new grey standyne and cable from leroy.

Check PMD connections and grounds. maybe make sure the solenoids inside the pmd havent vibrated loose.
Click to expand...

solenoids in a PMD???
 
Take the pmd off the cooling plate then look at the back side. There should be 2 solenoids (or atleast that's what it call them) they are held on by 2 nuts and they can vibrate loose sometimes.
 
tanman_2006 said:
Take the pmd off the cooling plate then look at the back side. There should be 2 solenoids (or atleast that's what it call them) they are held on by 2 nuts and they can vibrate loose sometimes.
Click to expand...

Transistors


Some PMDs will cause the issue. Check the easy free stuff first. Try pluging PMD/heat sink back onto the truck harness to eliminate the ext cable. This assumes it will do it on a regular basis.
 
Were you in reverse at the time? I've had my 94 do that a couple times, in reverse only, in the past two years. I had just put in a new PMD. Engine speed never went very high, more like a blip of the throttle. Except my foot was not on the throttle, only the brake. Never a hint of that in any forward gears.

Don
 
handcannon said:
Were you in reverse at the time? I've had my 94 do that a couple times, in reverse only, in the past two years. I had just put in a new PMD. Engine speed never went very high, more like a blip of the throttle. Except my foot was not on the throttle, only the brake. Never a hint of that in any forward gears.

Don
Click to expand...

Just wait, it will get worse. Mine would do it primarily in reverse(probably 100 times in reverse, maybe 5 in forward). New ECM cured it, but the head gaskets let loose shortly there after and I decided to do the engine swap.
 
handcannon said:
Were you in reverse at the time? I've had my 94 do that a couple times, in reverse only, in the past two years. I had just put in a new PMD. Engine speed never went very high, more like a blip of the throttle. Except my foot was not on the throttle, only the brake. Never a hint of that in any forward gears.

Don
Click to expand...

Yup.
twice now...
both times in reverse.
both times after rapidly changing from D to R to park or turn around the truck...
ECM eh... CRUD...

WOW the truck sure has some grunt in R... tires break loose ... I will SOOOO never put the truck into reverse without my foot on the brake!!!
 
No guarantees on ECM, vstech. Hate to disagree with Ferman, but mine was most definitely PMD, and I've seen the same behaviour on maybe a dozen trucks that a new PMD solved.

Wish mine WAS ECM... Could have gotten a performance re flash at the same time.

I have also heard of some trucks where bad harness, or filter, or optical sensor would do the same thing. These IPs are electronic, so any source of transients can cause issues.

Since there wont be any codes (most likely), about the best I can suggest is that you troubleshoot one thing at a time, do the cheapest stuff first.
 
well, the SES light is on all the time right now, so I'll tackle that first... once I get the codes fixed, I'll begin troubleshooting the revving issue...
 
Don't let that one wait... The part that got to all of us was the unpredictability of the surge... We wondered if it might happen when somebody was behind us, walking between us and a hard place.

me, I wondered if it would next happen with my wife driving, because that would pretty much be the end of all life as we know it. :D
 
ok...

I'm still having this issue... yeah I know... LOOOOONG time between posts.

anyway, I ordered the kit from leroy, got the FS PMD and extension... truck preforms nicely, but still does the reverse gunning...


it does it differently now... not a solid blip of the throttle anymore, now with the FS, it will BRA BRA BRA in R... still no change in Forward gears... I'll open EVERY ground connection and clean and tighten them... then I guess I'll get a CPU... fun
 
Out of curiosity, have you tried the 2K RPM cycle test?

Mine did a Grrrrr WHUMP WHUMP (felt like a stutter, surge, surge) with my foot off the pedal (in any gear). Also, it failed the 2K RPM cycle test. New IP fixed it.
 
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