Injectors or IP?

[JTodd]

I am having some very odd symptoms, but I am not sure what they point to. Occasionally, while sitting at idle, there is an odd 'pop' of too much fuel going into a cylinder. It hits hard enough that it feels like someone ran into the back of me. When this happens, there is the tell-tale puff of black smoke. It has happened while coasting, off throttle, on the road as well. Never while on throttle. Now, a new thing is happening. Twice in the last week, while on the highway, the truck will accelerate, almost at full throttle, for about a second. This is not a pop, but more than that.

Are these symptoms of bad injectors, which have not been changed in quite a while, and may have 150k miles on them, or are these signs of the injector pumping failing?

[Robyn]

The two different symptoms are basically the same thing.

This is IMHO the more rare of the PMD failures raising its ugly head.

How old is the current PMD??? Change the thing.

The most common PMD failure is a stall and then restart followed by a no start at all.

The other issue is a runaway that continues until the engine reaches REDLINE and then the computer shuts the engine off using the shut off solenoid.

The Shut off solenoid is not the primary way that the engine is shut down, but instead a safety that physically stops the fuel from reaching the inner workings of the IP.

I wont say that it is not a Possible IP failure in progress, but its likely the PMD in its death throes.

Try a PMD. I like the Dtech units.

I will not use the new Stanadyne grays ones for one reason. These clowns hung us out to dry for years and years and only after the aftermarket got a good one, did they come out with a better unit.

Just some info on the PMD failure. The POP or rap you are hearing and the BUMP is probably due to a circuit in the PMD thats failing, allowing the throttle to go to full fuel. I have never seen one behave just like this, but anything is possible. The normal failure is that the circuit burns through and the thing runs wild for a few seconds until the ECM shuts it off.

Cranking at this point will yield nothing, but turning the KEY OFF AN BACK ON and cranking will see a repeat of the same runaway.

This can get real interesting if it happens in traffic :eek:

Keep us posted

Missy

[ronniejoe]

Check for codes. Look for solenoid closure response time too short or too long. Then, if you have a scanner, record the response time and look at it graphically. If you see erratic swings from really short to really long response times, it's either the FSD or the pump. Try the FSD first, since it's the cheaper, easier fix. If that doesn't do it, it's time to change the pump.

[JTodd]

I will try the FSD first. I have had a couple of them go out since owning the truck (8 or so years) and this is unlike the others. Previously, it would dye like it had run out of fuel, and would restart from right away to after it had cooled, depending on severity of problem. I believe this is a different brand, the first couple being Stanadyne, so maybe it is this brands way of failing.

Thanks for the input and I will report back what i find out.

[JTodd]

I put a d-tech PMD on and the issues are about 95% gone. I still have a couple "pops" when I get off the throttle, but this happens infrequently, so I think it is more a bad injector. There have been no self throttling as before, which were on the verge of being pretty dangerous. I guess the Stadyne PMD just quit and the dtech units get all hinky.

Thanks for the help and suggestions.

[Robyn]

Glad that the gremlin is taken care of. Hope that things stay working good for ya.

You might want to install a fresh filter harness. This is the little small wiring device that connects from the top of the IP (optical sensor) to the main engine wiring harness. It has a little rectangle shaped black box in the harness. This harness is about 6-8 inches long.

The filter is supposed to filter out unwanted electrical "NOISE". An errant bit of electrical noise in the optical sensor circuit can cause wierd crap to happen.

If the harness is the original, its a good idea to replace it.


Missy