My truck was cuting out (like a miss fire) above 1800rpm's. I looked back through the forum for diagnosis with this problem and all of them pointed toward's the OPS/liftpump/filter. I changed the filter which was full of cr*p, but that didn't help my problem. The lift pump was pumping plenty of fuel, so out with the OPS/liftpump as suspects. I thought it might be the tranny, but it was cutting out just rev'ing in park. So I turned my attention to the accessories possibly binding at high rpm's.

This is where I used a trouble shooting method I think could help some people out when trying to diagnose a problem, it worked for me. I pulled the accessory belt off and started the truck, the miss was gone. I only ran the truck for about 20 seconds keeping an eye on the temp guage, but I think it would take more like 3 minutes of intermittent reving to over heat the engine.

My PS pump was leaking(at the shaft seal) so I changed it hoping this would also fix the miss. It did not, but my leaking pump was now replaced with a lifetime warranty pump from the ZONE for $58.:)

I knew it wasn't my AC it hasn't been used in month's. I checked the ALT and the vacuum pump, but niether of them were strong enough to make the engine choke, in my opinion. I have a new HO water pump in the garage, but there didn't appear to be anything strange going on with the water pump on it now.

This led me to the culprit, the belt tensioner pulley, but not because there was anything wrong with it.

My belt was so old, cracked and stretched that it was allowing my tensioner to be pulled past vertical at high rpm's, this action caused the belt to pull the tensioner tighter and tighter against itself durring high rpm's, basically trying to suck all the accessories together creating a momentary high load.

This might seem like a strange fix to what felt like a miss fire problem (it did to me), but before I changed the belt I couldn't get the rpm's past 1800 without having the strong hesitation.

I've been running past 3000rpm all day now without missing a beat, and my problem is gone (you just know when thing's feel right).

Anyway that's my story and I'm sticking to it, I hope my method helps someone out there hunting down a problem.

The belt was slipping, more than likely. How much tension on the arm? they get sprung after awhile.

Hmmm....I wonder if this isn't what's going on with my truck too. I've noticed while the truck is idling, surging or not, that the tensioner arm whips back and forth quite a bit, and it also seems like its not in the position it should be....
I replaced the tension arm because it siezed up, damaged the belt a little but I never replaced it. I think I'll try that, thanks MDT.

Good story - possibly the alternator pulley was slipping, allowing voltage surge\decay spikes, known to mess with the Optic Sensor and FSD\PMD.
An add-in OS filter was required to prevent just such things, amongst others.

I already tried that a couple times on mine, I've got a chain of the long enough for a jump rope ;)

Even when the belt is new and the tensioner is in the correct range I don't like the angle the tensioner sits at. I'll put it on my list of bad designs. Interesting this accessory arrangment only lasted 2 years 94/95 maybe someone at GM noticed this problem.

The tensioner is totall different on the '96+. The accessories all switched from small block to BB. The alternator and A/C compressor switched spots along with the tensioner. Plus on the eary models it takes a 18mm socket to move it and on the newer it's a 3/8" driver not a socket.

Iirc - the change was to a totally different a\c compressor, requiring new bracketry.

I stinkso I got bof' types when I was buildin' my truck, back in '99.

Wow! Seems like another time, another century, now.......... ;)

Even when the belt is new and the tensioner is in the correct range I don't like the angle the tensioner sits at. I'll put it on my list of bad designs. Interesting this accessory arrangment only lasted 2 years 94/95 maybe someone at GM noticed this problem.
94/95?
What about 88-93? As far as I know, they are the same too. My 93 has the exact same accessory arrangement as my 95.

MDT, I can't thank you enough for starting this thread, ordered a new belt for my truck today and the guy at the parts house said he showed two different belts and didn't know how to tell which one I needed, but said he would gladly send them both for me to try and let me return whichever I didn't need. So, tonight when I got home, and I don't know why I never noticed this before, but the marks on the tensoiner arm were not even close to being lined up, the arm was pointed straight down. I pulled the belt off and sized it up to the two new ones, the longer of the two was an exact match and the other was a good 5~6" shorter, so I installed that one. What do you know, the lines are lined up right and I really hope this is the final cure to the incurable surge at idle trouble I've been having! Going for a test drive, to the beer store, thanks again MDT!

What's the number you used ?

I'll check in just a minute.

Goodyear Gatorback 4061010. The other one they gave me was 4061020.

I think the Zones computer is wrong for my truck it called for the 4061010, but thats the belt I run with the vacuum pump removed. I think if the vac pump was still on it would have needed the 4061020.

Whatnot, I have never seen under the hood of the 88-93 diesel's, so I didn't want to speak to them, but I do know that under the hood the 94/95's are practically identical and that changes came in the '96-up changed aroungd the accessory configuration alot.

When I was finding my belt at the Zone it showed 4061000 as the part # for pre '94 so something should be a little different.

For anyone trying to make sense of the number system the last four digits are significant of the lenght the first three identify it as a serpentine belt. I don't know why they choose 1000 as the reference point, but the last two digits are increments in inches. Ex. 4061010 is 1 inch longer than 4061000 and most belts can be found in 1/2 inch increments so a 4061005 would be right in the middle of the two mentioned before.

I just did my '98.

Belt without pump is 4061000 at Autozone, or 4061010 with pump.