98 Sub new 6500 missing

[bl78ljb]

Ok, I have read a lot of the posts here and cannot find (though I could have over looked it with the vast info present here) my problem. I have a 1998 2500 Suburban 4x4 with the 6.5TD. When I purchased the truck the seller neglected to tell me about the slow coolant leak - turned out to be a cracked block. So it now has a brand new Optimizer 6500 engine with 2 year warranty since I had my mechanic install it (didn't have the time to do it myself and I needed the truck ASAP). Shortly after getting it back I had a lot of trouble with stumbling / stalling and no power going up hills. Turns out the fuel filter housing had a casting crack (replaced under warranty with new fuel filter) and the lift pump was bad (replaced my cost). That resolved the no power up hills problem, but I still had stalling when hot so the FSD was remote mounted and replaced with a DSG kit (covered under engine warranty). Now I still have an occasional stumble / miss which yesterday became steady at 1500 RPM during a drive through no-where Maine. At first I noticed this at 50MPH in 4th (4L80E) and thought it might be a torque converter not locking correctly, so I shifted into 3rd and the problem went away until I sustained 35MPH at 1500 RPM again. I am sure the mechanic is not going to be happy to see the truck back again, and I cannot afford to have it down for a long time as it is the only vehicle my whole family can go out in at the moment. My question is first of all does any one have any experience with similar problems and second is there a PC based (laptop) diagnostics I can run while I am driving to see record the data stream to bring to my mechanic (as he couldn't get it to act up the last time he had it)? Also any comments on the DSG FSD cooler it was free so I cannot really complain too much! I also wanted to thank all those who helped me diagnose the cracked block back in Feb / March (though my wallet didn't like it very much).

Bryan Lundquist
Bangor, ME

[tommac95]

I hope you took the oportunity of the engine swap to assure the cooling system is working well , no debris behind condensor , etc. Sorry to hear all the problems. Sometimes fuel filter problems are indistinguishable form FSD/PMD symptoms. Hopefully you've checked/monitored LP pressure and maybe delivery , to rule out bad fuel , and fuel starvation.
* *
There are now finally at least a couple laptop-based programs to monitor your vehicle powertrain operations. Your 1998 is OBDII {OnBoardDiagnostics, Second version} , and i'm not too familiar with the options available. The problem has been most scanners did not did not show much of interest for diesels, {and secondarily , only the $1500+ arrangements allowed interactive settings}.

My records include readers for gas obdii Saturn , diesel obdi 6.5L , and VW.

Thus I suggest you do a search until somebody else offers good advice... use terms "scanner" , "codereader" , or "code reader" , combined with "laptop".

I think you'll encounter sites like :
http://www.autotap.com/products_trucks.html
and
http://www.obdII.com/

http://www.obd2.com/

http://www.obd-2.com
(???)
Some people have had good luck with stuff from ebay , too....

T m.

[Shikaroka]

I'm not going to be much help with your missing problem, as I think I have a similar situation.

As for scanners:
CarCode, www.obd-2.com , should do what you want. I have it and I am still learning how to use it, but it is quite nice. It's also one of the cheapest options and upgrades are free. There are several CarCode users on here.

[JohnC]

If your engine is equipped with EGR, the EGR system has been known to cause missing around 1500 RPM. However, I don't know much about post '95 EGR systems...

[bl78ljb]

To add some additional information, I was told that the truck was smoking a bit on Sunday before it really started to act up reliably at 1500 RPM. Also the whole cooling system was gone through as there was some cross contamination between coolant and oil and all lines / hoses were replaced, the radiator was removed, hot-tanked and pressure tested; and the oil cooler was replaced with a new OEM one due to warranty requirements for the engine. Also the cooling fan and clutch where checked out and tested and found to be fine. The LP is new as of 3-4 weeks ago and rechecked 10 days ago and was working fine at that time and the fuel filter was replaced with the engine in April and again 3-4 weeks ago, and since then I have only run about 2.5 tanks of fuel through from the local truck stop (VERY busy) and they actually have a "bad fuel" guarantee so they keep up on their fuel.

Thanks for the info so far.
Bryan Lundquist
Bangor ME

[tommac95]

Ah , Bryan
read thru this thread , you may be seeing fuel starvation:
http://www.thedieselpageforums.com/tdpforum/showthread.php?p=214069&posted=1#post214069

[bl78ljb]

Well, I put 100 miles on the truck yesterday and it ran great I even tried to run it at 1500 RPM for a while and couldn't make it hiccup. Now I was wondering (and this is the main reason I tried it in 3 at 1500 rpm), but would a tranny problem cause this - the torque converter shouldn't be trying to lock in 3rd at 35mph, but possibly a sticky solenoid or other electronic or mechanical control?? As far as the LP is concerned I would think that if that was bad I wouldn't have power when I stepped on the gas which seems to clear it up, and also like I mentioned before the shop just checked out the lift pump again a few weeks ago. The main reason I am trying to get to the bottom of this intermittent problem is that I am going to be taking a road trip from Maine to Chicago at the end of July and don't want to end up on the side of the interstate somewhere in between.

Thanks

[tommac95]

>As far as the LP is concerned I would think that if that was bad I wouldn't have power when I stepped on the gas
Agreed , neglected that. I haven't had trans problems , others have , and with lockup, and APP [accelerator position pedal , or sensor , whatever?] , commonly.

[bl78ljb]

Well, driving the truck today it finally hiccuped again, and I happened to be looking at the gauges when it happened, and it was at slightly over 1500 rpm and it dropped between 200 and 400 rpm with the hiccup. I would think that with this happening it would not be a transmission problem as the torque converter should isolate the engine from a loss of rpm (though a slip would allow an increase in rpm this is not what seem to be occurring). Also when this occurs it seems to buck enough everyone in the vehicle notices. If the fuel filter hadn't just been changed I would think this would be the problem though it goes away for a few hundred miles and comes back (which I don't think a fuel filter would do at least not so in my experience with gas vehicles). A couple of questions, could a bad OPS cause something this intermittent that seems to resolve by giving it fuel, does the fuel pick up in the tank have a sock on it like an EFI gas engine, could the electronic throttle control be this intermittent and cause a similar problem, and could I be off base and this actually be a tranny problem?

Thanks again

[a5150nut]

Well, driving the truck today it finally hiccuped again, and I happened to be looking at the gauges when it happened, and it was at slightly over 1500 rpm and it dropped between 200 and 400 rpm with the hiccup. I would think that with this happening it would not be a transmission problem as the torque converter should isolate the engine from a loss of rpm (though a slip would allow an increase in rpm this is not what seem to be occurring). Also when this occurs it seems to buck enough everyone in the vehicle notices. If the fuel filter hadn't just been changed I would think this would be the problem though it goes away for a few hundred miles and comes back (which I don't think a fuel filter would do at least not so in my experience with gas vehicles). A couple of questions, could a bad OPS cause something this intermittent that seems to resolve by giving it fuel, does the fuel pick up in the tank have a sock on it like an EFI gas engine, could the electronic throttle control be this intermittent and cause a similar problem, and could I be off base and this actually be a tranny problem?

Thanks again

Have you had a chance to pull any codes? Either use a scanner or have it done at local parts store. This would help a lot to determine whats wrong here.

They will run without the lift pump working so I would think a bad OPS would also run.

[moondoggie]

Good Day!

I don't know what's wrong with your truck, but some ideas:

1. Don't look at the LP, OPS, or individual parts 1st, look at the LP SYSTEM, until you've determined it's working or not.

The LP system is powered two ways: 1) during cranking; 2) during running. On older 6.5's like mine, the LP is powered through a realy during cranking, & through the OPS during running. On newer ones like yours, I think the LP is powered by a PCM-controlled relay in both modes, but still has an OPS to tell the PCM if the engine's running (so it can shut off the LP when the engine quits, like during a wreck).

Crack open the air bleed on the front of your engine (mine's bolted to the thermostat housing, yours might be elsewhere). If the engine dies, you LP SYSTEM isn't working (& it's gonna be a bear to restart); if it continues idling & starts squirting fuel wherever it is that this valve drains, your LP SYSTEM is probably fine, no need at this point to look at either the LP or OPS.

2. Most of the time, if the LP SYSTEM isn't working during run mode, it will feel just like a gasser with an ignition miss: missing/jerking at heavy footfeed. (There are other manifestations than this, however.)

IMHO the EGR is worth looking into, unless of course your truck doesn't have one.

Let us know how this turns out.

Good Luck & Blessings!