John8662 reSmoke at start up

[nigeljones]

John

I didn't get to swap the pump out this weekend. To many other things todo.

I was debating just to put a new/rebuild pump in and do the job once.

Based on that, I took the truck to work today and had the scanner attached. The truck was hesitating between 60 and 70mph. However, I did not have any codes. Now I'm baffled.

Do you have any experience with the throttle/pedal sensor. I was wondering if it was something to do with wear on the potentiometer.

OR how about the Cat plugging? or how about the ECM?

I have a new PMD but I'm going to swap that out with another just to rule that out.

Feed back appreciated

[john8662]

Nigel,

I don't think it would be the APP, there would be a code associated with it, or the transmission would be acting up too. Usually hesitation like you're describing is associated with low fuel delivery to the injection pump or clogged fuel filter. But you've already hit those bases in this game. I'm with you though, install a reman pump or at least have your spare pump tested, it's really not a fun job to do twice. I swapped out IP's on my 95 troubleshooting the knock I was getting. It was the last ditch effort because I was told that a DS4 pump could have a poppet valve bad and lose just one cylinder, which doesn't happen on a DB2 pump. Anyways, one of my good friends who is a diesel mechanic told me I was crazy for doing it as it was alot of work just to see if it was it. But who knew, until I swapped it that it wasn't it. The noise became louder and more pronounced all of the time, so I'm awaiting my new engine.

Anyways (I get carried away) I also don't think that the Cat is the problem, it usally chokes up the engine and it will have no power and usually no black smoke out the pipe.

I vote for new injection pump. Take the 5521 down to a Stanadyne shop and see if they'll test it for a reasonable fee. Most shops with the appropriate equipment will, but it's pricey. On another note, I've been told you really can't "test" them because there are so many variables that play in this game on the engine itself. I don't know which is true. I got lucky on my spare pump I picked up on ebay, but the majorty of the pumps on ebay are junkers, but some just have bad PMD's etc.

[slagona]

I've used Superior Turbo & Injection in Detroit to test pumps in the past. They were well under 1/2 the price when compared to the outfit in Sterling Heights. They are also DE Certified, whatever that means - Sterling Heights is not.

Just called Superior, they are $75 each for bench testing - it's gone down in the last 2 years.

Yes, I've also heard - and agree - that a bench test certainly isn't conclusive as to a pump's operation. There are too many other factors involved that aren't covered during the bench testing. However, it certainly can tell you if the pump is still developing proper psi, etc.

--Scott

[nigeljones]

Thanks for the input. I was out driving last night with my Gas Mechanic friend and his SnapOn Scanner.

Our findings weren't conclusive but what we did notice was, that when the vehicle is at my normal cruising speed of 72mph, engine rev's are approx. 2200rpm and backing off the gas as you crest a rise in the road to maintain your speed. When the APP% hits between 12-14% that's when the hesitation starts. During this the torque converter was locked up, so nothing funny there and when we drop the trans into 3rd gear and again performed the above test around 2200rpm backing off the gas and around 13%APP the hesitation starts.

Is this the Throttle position sensor?

Thanks

[john8662]

No throttle position sensor on the DS4 pump. The DB2 injection pumps on a 6.5TD were equipped with a TPS for 4L80E operation. I can't say that I've connected a scanner running live down the road for this test to know if this is the problem.

Do you know anyone else that has a 6.5 that you could swap out the APP to see if thats the problem? Like I mentioned earlier, when the APP isn't operating as it should you will get a code.

[nigeljones]

John I thought the throttle position sensor was part of the pedal assembly.

I had seen on the SSDiesel web page whilst looking for a new pump that he now sells them and was this now my issue.

I really am now grasping at straws.

Thanks

[john8662]

So the engine mainly hesitates at above 2200 RPM? What happens with you reving the engine parked out of gear? Does it do anything odd then?

You're right on the APP being somewhat of a TPS. Because it gives the transmission the throttle position as well as the signal to the IP for fuel.

[ 05-25-2005, 09:43 AM: Message edited by: john8662 ]

[JohnC]

The pedal assembly contains 3 separate position sensors. They opperate in different ways and the PCM constantly compares the 3 readings. It is next to impossible for them to act up in a way undetectable by the PCM. If there are no APP codes, I'd look eslewhere.

Does your engine have EGR? If so, you may want to look there...