HELP
I replaced y faulty VAC PUMP and now 2 serpentine belts. The belts keep stretching. When the belts are "new" i don't have the problems. But it only takes a hour or so for the belt to stretch out. now the main problem is this. When i am cruising at 60ish 1800 rpm the truck starts to surge may go up to 2500 RPM. I feel alot of power but not much acceleration if any. Surge lasts less than a second and then there is alot of black smoke. after misreading a post i removed the vac pump and got the "no turbo boost vac at solenoid" or something like that. so i replaced the pump and reset the codes through with my friends scanner. after resetting the codes i got a -40 engine temp code. I figured this was because i reset the codes. cant scan again till tonight. The check engine light has not come back on.

so in a nutshell
replaced vac pump
replaced belt
reset all codes
got a -40 temp code which i ignored.
noticed new belt had stretched to the limit and had some rubber shavings on the passenger side battery
replaced belt again (stretched like the first one within an hour or so)
cruising at 60+ mph the damn thing surges and blows black smoke.
noticed the radiator hose is not hard, even when hot, but i have plenty of antifreeze.

surge almost feels like the overdrive is going in and out




1. Does the engine crank, or 'turn over'? YES
1a. Does the engine start and run? YES
1b. Do you have a Wait To Start Light & the amount of time (seconds) lit. YES, TIME VARIES 1-5 SEC
1c. Ambient Condition (temperature outside) 90F, 70F OVERNIGHT
1d. Engine Cranking speed (if you have an accurate tachometer). ??
1e. Are you experiencing stalling? NO
1f. If Stalling, describe (upon startup only, down the road, hit a bump etc)

1g. If Stalling, do you notice loss of dash or instruments?
-note if experiencing stalling,you must indicate PMD location in #24.
1.1 Lift pump test - describe results PLENTY OF FUEL AT FILTER BLEED
2. Service Engine Light while running?- on/off/intermittent OFFbut had a temp sensor code -40 degrees
2a. Service Engine light does glow during start/cranking/bulb check: Yes
3. Model year 1998
3a. Odometer reading (indicate if in miles or km) 114,000 miles
3b. Miles on major engine components if been replaced (example Injection pump) 15K ON NEW PUMP
3c. Indicate the model number on the Injection pump (starts DS4 or DB2......) NOT SURE, WHERE DOES IT SAY?
4. Have you scanned for engine codes? (varies by pre/post 96) yes/no YES
5. List exact results on engine codes: engine temp -40 and no boost vacuum fixed the no boost with a new vac pump

6. Air Filter condition (visual check) clean
7. Fuel filter condition (freshly changed/condition unknown/mileage since changed) IN LAST 1500 MILES
8. Condition of Battery terminal connections (removed, cleaned and tightened) CLEANED and greased
8a. Known condition and age of the batteries. new in spring
8b. Are batteries of differing age or are they a matched set? MATCHED
8c. Condition of Major Grounds. (same drill as batt - removed, cleaned, retightened) CHECKED BATTERY NEG TERMINALS TO ENGINE AND CHASSIS AND ALL READ GOOD
9. Upon cold start, does the radiator hose get hard quickly? NO its not getting hard at all
10. Upon cold start, do you have excessive white smoke? Yes/no NO
11. Do you have excessive cranking time before the engine starts? Starts Great
12. Have you used the block heater, and does this effect engine starting?(only try for starting problems) never used it
13. During hard acceleration, do you have excessive black smoke? NO

14. Do you have any unusual exhaust smoke issues? YES When the engine surges
15. Turbo check out - pass/fail NOT SURE
16. Do you have an EGR on the engine? (An F or an S engine code 8th VIN digit) F SERIES VIN
17. Indicate if you know if it’s a 1500, 2500, 2500HD, 3500, 3500HD. 2500
18. Indicate fuel that you are using: Bio-diesel, #2 Diesel, #1Diesel, SVO/WVO, other #2 diesel i think whatever they sell in Virginia
18a. If running a VO (Veggie Oil fuel) setup, indicate details of your conversion (homemade, or packaged system) HOMEMADE, STANDARD 2 TANK, 2 VALVE SYSTEM NO PROBLEMS
19. Are you using any fuel additives? If so, please list. not recently this year usually use it before a filter change
20. Please indicate geographic region you are in: (example: Texas or Canada) VIRGINIA
21. Do you have any service history available that might pertain to the problem you are having? YES, Vac pump was tapping. replaced it reset the codes and a -40 showed up for the engine temp (gage shows 160-180) tried 2 new serpentine belts, and both stretched to max per the tensioner. Seemed ok before the belt stretched about 2 hours.
22. Please indicate any modifications to the vehicle that might help us diagnose better. NONE its all stock
23. Upon unscrewing the fuel cap, do you have a large vacuum formed in the tank? yes/no sometimes
24. Location of PMD/FSD? On the pump/remoted over intake/remoted out of engine bay (please specify placement specifically) stock but i removed the plastic "TURBO POWER" trim piece
24a. If remote mounted, describe wiring harness (homemade or purchased from a vendor?)
24b. Indicate the location and condition of the FSD/IP grounding wire. stock
25. Are ALL glow plugs in proper working order as per this thread? YES

what belts are you using? i've had Dayco belts stretch like rubber bands on my truck, my old car, my dads truck, and on my friends 3.8 buick to name a few. i put a goodyear gatorback on the truck and it stretched a little bit then stopped and now it sits right in the normal range. maybe the pulleys aren't lined up quite right. it sounds like the belt is being chewed through if you've got rubber on one of the batteries. when you replace the vac pump did you make sure to get the pulley on it all the way. if its not on all the way the pulleys don't line up and can wreck havoc on a serp belt.

I agree the belt must be prematurely wearing from a misaligned pulley. but will this cause surging?

the first belt was a autozone generic the 2nd was/is a strauss (i think) generic. Pulley was out about 1/16th inch, as opposed to being flush with the end of the shaft. I turned it in 1/4 turn with my pulley tool and now its flush. it looks like it is in a little too much now but if the belt wore unevenly, from riding on the lip of the pulley, it may just wanna ride on an angle. Off to the store to get another one. Damn the belts are going to wind up costing more than the vac pump.

How is the tensioner? I don't recall if the tensioner is a problem on later years but on the 95 they are junk and over tighten the belt. Too tight and it will stretch the belt and ruin bearings in things that turn like the vac pump.

tensioner is good. Had to replace it about 1 year ago. The tensioner pulley actually exploded.

I agree the belt must be prematurely wearing from a misaligned pulley. but will this cause surging?

Beats me <lotsa help - eh?> But I wonder if the ECM is using the tach output from the alternator in any way?
Could the alternator's speed varying cause surging??

-40° shows that you get a problem with the coolant temperature sensor (CTS) located on the T-stats housing. When hot, disconnect the sensor, you will reproduce the problem.
My truck was surging too and I found that the problem was coming from the harness of the CTS, more precisely the plug itself.
I changed it, and no more surging

Mutuva; Where did you get the replacement plug? I need one.

at rockauto.com

I,ve got a 99 suburban 6.5 same issuses I actually brought it to a tranny shop. I also thought it was going in and out of the top gears, but it turned out to be the surginging. Also when I let my foot off the pedal it instantly drops to idle. occasionally will stall but start right away.new remote pmd. It makes for an exciting ride with the sudden burst's of power and all. I'm new here [1st post] . Thanks AF

Here (http://flashoffroad.com/Diesel/troubleshoot/troubleshoot.htm) is some good reading on surging, hope it helps!

Does a failing PMD cause surging?

I replaced the vac pump with a TM didnt stop my surging.

Gonna replace the ECM temp sensor tommorow. Hopefully that doesnt. If it doesnt Im driving my truck off a cliff to get insurance money :mad:

Does a failing PMD cause surging?

I replaced the vac pump with a TM didnt stop my surging.

Gonna replace the ECM temp sensor tommorow. Hopefully that doesnt. If it doesnt Im driving my truck off a cliff to get insurance money :mad:


Yup. A failing PMD can cause surging. The vac pump will not cause surging as well as stalling. My truck did the surging thing in reverse once and i almost backed over a honda civic's hood.

Yup. A failing PMD can cause surging. The vac pump will not cause surging as well as stalling. My truck did the surging thing in reverse once and i almost backed over a honda civic's hood.

Dammit I was in reverse yesterday and the whole truck was shaking like crazy for 2 seconds then it returned to normal.

PMD failure?

I already recieved the ECM temp sensor today and Im putting it in tommorow.

If that doesnt stop the surging then I'll get heaths PMD kit. If the PMD kit doesnt stop the surging then I'll push my truck off a cliff.

I still have a warranty for it but after reading all the horror stories here about dealers I dont want to take it to a shop

Dammit I was in reverse yesterday and the whole truck was shaking like crazy for 2 seconds then it returned to normal.



Sounds like what mine did. Sometimes it would rev up(~1500 rpm) and then go back to idle. Having that happen in gear is very dangerous as it could happen at any time. you could end up backing into something/someone or hammering the front of the truck into a car/person/building/etc.