I would like to bump the timing a little on the 6.2 in my 89 Suburban. Wondering how you guys get to the pump mounting bolts to loosen them enough to adjust the timing. Special GM tool or something more common?
Thanks in advance.

Just a regular ole fifteen millimeter wrench is what I used and then rotated the injector pump to the drivers side.

I would like to bump the timing a little on the 6.2 in my 89 Suburban. Wondering how you guys get to the pump mounting bolts to loosen them enough to adjust the timing. Special GM tool or something more common?
Thanks in advance.

I guess you must have cruise control... That can make it quite painful to get to the driver's side mounting bolt. There isn't a good way to do it. I am sure there is a special tool of some sort that is made for the purpose, but I don't know what it is.

I use a plain 15mm wrench and rotate the bolt the little bit that you can from the driver's side of the cruise control support bracket and then flip the wrench over and go through the opening on the passenger side and rotate it a little bit, then back to the driver's side, and the passenger side... It takes forever, but you only have to loosen it a little bit...

I suppose you might be able to buy a cheap Chinese 15mm wrench and bend it a little bit to make it simpler... I've never tried it though so I don't know if that would work or not.

Thanks guys, I do have the cruise (doesn't work, don't really care) and it is in the way. I can do the slow way.
I'm hoping to bump my mileage up a little and will post if it makes a difference. Got 220K on the chain.

Mine is pretty easy to do, but I use a gearwrench, so its nice.

Update: Should have moved that timing forward a little a long time ago! Hasn't started this well since I've owned it. Starts immediately at the end of the regular glow plug cycle when cold. I had to hold the manual override for several more seconds and it would still want to crank for several seconds before firing up. And warm starts without the glow plug override being used for 7 seconds where nearly impossible. Now its just a few revolutions and off it goes. I'll let you know how it goes with any mileage changes. I'm getting 13-15 right now. It used to get 17-20 when my little brother owned it. I'd be a lot happier at 15-18. Thanks for the feedback it was a pretty easy task.

whats the history on the injectors? more than likely it needs them cleaned, or new ones. thats probably where your mileage is. Mine was still running smooth, but they all sprayed bad, and two were really crapped out.

Update: Should have moved that timing forward a little a long time ago! Hasn't started this well since I've owned it. Starts immediately at the end of the regular glow plug cycle when cold.

Sometimes guys will rotate the pump if the timing chain has seen a considerable amount of miles.It probably does have a little bit of stretch in it.

It has a few miles on it. Like 246,000! Going pretty well actually. Uses a little oil, not too bad at all really. Pump and injectors were done around 130K so I'm sure I'm due. It runs well. I did take a 700 mile round trip east from Seattle on I90 to just this side of Spokane and back west on Hwy 2 across the snow covered high plains to Waterville, Wenatchee, Leavenworth and back to the big city of Bothell. My mileage bumped a little to about 15mpg. I was rolling about 65-70 eastbound and about 45-60 Westbound. Seemed like it smoked a whole lot less too. The weather was cold, but it seemed like it ran cooler, too. Is that possible from just getting the pump timing straightened out?

Well, the IP and injectors are probably getting worn. That is probably the cause of the poor fuel economy. The advance piston on the IP is probably wearing out, which is causing the smoke. Advancing the timing a little bit would help with the smoke and gas mileage. I don't think that is why it ran cooler, though... That is probably due to the cooler outside temperatures.

That is the static timing you adjusted... There is also an advance control on the injection pump which advances the timing at higher throttle positions. Advancing the static timing kind of helps because by doing it you get the timing close to where it needs to be at higher throttle positions. The problem is that if you do that it is probably advanced a little too far at idle. Doesn't really matter... The advance piston fails frequently on these pumps (the one on my truck is nonfunctional - can't afford to get it fixed - and it will probably run just fine like that for quite a while).

To see if that is the case with your engine, look under the hood with the engine running (be careful of the fan - but you knew that). On the passenger side of the injection pump underneath the throttle shaft you will see an arm that comes down and pushes on a plunger. If you were to race the engine you would see that it is operated by the throttle. With the engine idleing, push the lever all the way in. Let it back out and then push it back in again. See if it makes any difference which position it is in. If the engine sounds the same no matter what you do with the lever, then your injection pump is like the one on my truck... Partially inoperable... ):h

Anyway, that's my guess on what is going on with that truck... I wouldn't worry about it too much, though... That's a fairly stable condition, although it may not be the absolute best. :)

So you have a suburban that gets 15mpg high way?
There is some thing wrong with it. Last time I got 15mpg on the high was when I was towing my camaro as fast as the truck could pull it North on I-95.
Another time I got around 15 mpg is when I had a fuel leak from my lift pump, I was driving it like that for all most a month and didn't know it.
I have a newish injector pump, old stretched chain form the factory and the injectors look real old.
I know the chain is stretched out is because I poked it around with my finger when I was replacing the connecting rods and main bearings.
Last tank I got 15.7 MPG in hard core city driving.
The only road trip I wasn't towing any thing I got all most 25mpg.
One thing that will help you starting is an 00 gauge battery to starter cable.
After the 00 gauge starter cable it was like a different truck.

Yep, 15 is pretty low for a diesel on the highway.

And it is now midnight... I think it is time that I go to sleep. ):h