New problem,heat related?

[Yukon6.2]

Hi all
My 97 3500 5 speed tow truck has presented a new problem,which i'm hoping someone else can shed some light on.
Ever since i swaped motors,it's had a glitch which would make the motor buck on deceleration.If you applied just a slight touch to the skinny pedal it would go away.I'v been trying to get exact situation when it happens.It seems to begine as soon as it warms up a bit.Yesterday i was on a tow,very hot day coming home there is a long hill i was coasting down it playing with the pedal keeping track of the bucking,trying to keep it smooth and yet keep my speed down.The bucking will start at any rpm but gets more violent as the rpm's drop.Anyhow get to the bottom and i have no pedal responce.It would run fine at idel but try to accelerate and it would begine to buck.I limped it home 5 miles,found that you could give it light trottle till the rpm's hit around 1000 then the bucking would start,shift up a gear and same thing.Lugging up some small hills it would pour out black smoke and as soon as you tried over 1000 rpm it would buck.
Got to the shop and still no throttle responce when sitting in yard.
Let it sit overnight in shop,and it's back to normal.I noticed some running eratic prior when it warmed up,this was on other ocassions.
It's got a remote mounted dtech,fuel filter is fresh,lift pump appers to be working,i changed the optic encoder last mounth when it was down,fired right up after,but it had this bucking glitch prior to changing the optic encoder,and remained unchanged after.It never triped the ses light,i will try to pull codes today after i get my scanner back.
When it was down last mounth i also changed the pedal assembly which never made any differance.
So anyhow HELP:confused:
Thanks All Thomas

[joed]

Sounds like you've ruled out the FSD, so the actual Fuel Solenoid on the IP is probably sticking.

My 98 (also a 5-spd) would do this - seemed to be worse under load (towing), when shifting gears. Sometimes after I would shift, there would be no accel pedal response, wait a few seconds and it would usually recover.

I think the manual trans truck are worse for this, since the programming shuts off fuel on a no-throttle deceleration.

In my case, it was just how the IP was set up (was a GM warranty replacement) - it showed long fuel solenoid times on a scanner (~2.0ms or more, I think 1.95ms or less is recommended).

It would consistently throw a P1216 code.

Fortunately it didn't get any worse, so I just lived with it.

You might try a heavy dose of fuel additive - that may help it 'unstick'.

Hope that helps, Joe.

[Yukon6.2]

Hi
What controls the fueling when the throttle is in the idle postion?
And is the fuel solinoid a changable part? I'm thinking i'ts the same as the fuel shutoff?
Thanks Thomas

[JohnC]

What controls the fueling when the throttle is in the idle postion?
The PCM meters fuel to obtain the desired idle speed. If you are coasting in gear the fuel will be shut off completely above idle.

And is the fuel solinoid a changable part? I'm thinking i'ts the same as the fuel shutoff?
Not the same and not replaceable by mere mortals. It requires precise adjustment.

Your bucking may be due to the PCM not being able to smoothly handle the transition from idle to off idle. What resistor do you have installed? I've seen cases where a #9 resistor, probably combined with a sticky solenoid, caused bucking and erratic behavior just off idle.

[Yukon6.2]

Hi
I have a #5 resistor installed.I might try a different fsd just to rule it out,simple swap.
Went on a short job in town yesterday and it started and ran ok but i noticed irregularaties in the way it ran after it warmed up,seemed a bit finiky after it was started but defenetly gets worse as it warms up,still hasen't set the ses light,hoping to hook up scanner today to se if there are any codes that havn't set off the light.
Thanks Thomas

[Yukon6.2]

Hi
Had a chance to pull codes.
P0219 engin overspeed
P1216 Fuel solinoid response time to short.
The ses light hasn't come on since the throttle problem.
Any direction as to areas to check out?
Probly havn't put 500 miles on it since the problems i had in may,when it had the same codes plus a couple others,at that time i changed the optic encoder which got it running again.
Is there a test for the crank position sensor?
Thanks for the help
Thomas

[JohnC]

P1216 Fuel solinoid response time to short.


There's your bucking/throttle problem. The only hope I know of is to run a heavy dose of a good fuel conditioner and hope it settles down. Otherwise I foresee an injection pump in your future...

[joed]

If the additive doesn't help, since you are in Canada, you might give Westers garage a call about reflashing your PCM.

I purchased Westers tuning software a few years ago when he was offering it for the 6.5 separately and found that there's a PMD rpm constant that can be changed. I believe it's called "Minimum RPM for PMD failure diagnostics". The default is 1500 rpm, I increased it to 3000 rpm. After I did this, no more P1216 codes and no more hesitating.

Kind of a band-aid fix, and it may be cost prohibitive, unless you were planning to get a performance program anyway. Should still be less $$ than a new injection pump.

Just a thought as your truck may respond differently - sounds like it acts up (bucks) more often than mine did.

Joe.

[Yukon6.2]

Hi
I'll try a heavy dose of additive again,tried it when the optic encoder was bad.
The pump shouldn't be bad,it has less than 10k miles on it,was a brand new pump,not rebuilt.But if one was going to go bad that fast it would happen to me:(
Anyone familiar enough with these pumps to point to what would cause the optic encoder to go so fast,and posibly the pump?It's a blue label one i don't remember the #'s.
if i have to change the pump it will be to a mechanical one,but this is my first electronic controled 6.5 and would like to diagnose and keep it electronic till i have the time to converet the fuel system,being a standerd makes it an easy conversion,the next one i get will probly be an auto,so having experiance with the electronic pump will be an asset.

[Robyn]

The reason the encoder failed can be traced back to the fact that it is an electronic device and with that it is always at risk of failure.

Generally though, the optic sensors usually are fairly reliable.


Missy

[JohnC]

Contaminated fuel?

[Yukon6.2]

Hi
I'm biased when it comes to the fuel,99% of the fuel we use comes from our own pumps.Right now our diesel sales are high and we are getting fresh fuel right from the refinerys once a week,a trucking company is building a subdivision and are using about 1000 gal a day,no reports of any problems from them.The filter in my p/u has been in use for 4 yrs/about 20000 miles and havn't yet gotten any water out of the drain,the filter in my wifes gasser has been in use for about 8 yrs now,went to change it about 4 yrs ago,but was as easy to blow through as a new one.Having said that we will probly get some junk fuel now:rolleyes:
I havn't had it out on a long job where it gets hot to see if it will repete the glitch,went on a long haul yesterday with my p/u and had no probs pulling hills with a good load,so i would probly rule out fuel .
I still want to try a different fsd,still semes to be heat related,at least the none responsive pedal only happens after a long drive and a long coast down the hill.
Thanks for the ideas
Thomas

[Yukon6.2]

Hi All
So it seems like i have a Dtech that has issues.
Changed it out with a know good stanadyne unit and was able to put some mile on it yesterday.150 miles and drove it hard,ran better than it has in months.Absolutly no hesitations on deceleration,no jerking or bucking.
So i have mixed feelings,glad i found the problem,but i wish it wasn't me that has to try and get warrenty on a 7 month old FSD,especally seeing that there arn't any reported failures yet.:(
Anyhow i see numerous phone calls in my future
Thanks for all the ideas
Thomas

[racer55]

At the other forum there have been several D tech failures reported,mostly with a racing condition as a result of the bad D tech pmd.
Your problem sounds opposite with a stumble on acceleration vs a runaway but you never know what condition will present.