Injector Pump Question

[SteveMc]

I replaced my broke 6.2 with a N/A 1997 6.5 into my 87 GMC Suburban. Also installed DSG Gears and Stud Girdle kit and had my DB2-4544 I/p overhauled.

Ever since the startup I have had a problem with the engine surging. First I changed the filter. Located and fixed a air leak at the filter. Changed the timing up and down. Replaced the CDR tuna can. Called DSG and they say the gears are not the problem as it starts great and has plenty of power.
Had the I/P put back on the test stand and it showed good. The shop says it is a good pump.

It idles great and a slow throttle change up to about 1150 RPM is fine. After that it will surge up and down about 100 RPM. This is setting still. On the road there is a fast RPM pick up after 1150 RPM, then if you push the throttle to accelerate it will power up just fine, but when you get to a desired speed, the engine surges up and down slightly. When you increase or decrease power all is well. At a steady RPM it surges, you and hear and feel it.

Is there anything in the I/P that would cause this problem that anyone knows of? I am about ready to find another pump and try that, but my money is short. Any suggestons appreciated.

Thanks SteveMc

[Peter J. Bierman]

How it the pressure from the lift pump?
It has been said that a failing lift pump can couse surging.

Peter

[SteveMc]

Lift pump tested at 9psi at idle. Then down to 6 psi at high rpm. Added an electric pump and filter to assist machanical pump, but no change in running. Example of problem. Running at 40 mph in drive with 1740 rpm on level ground. The engine will surge every three seconds. You can hear and feel it, but it isn't a jerk or anything like that. Just a constant hunting.

[Peter J. Bierman]

Timing?

Timing varies with RPM, the higher the rpm the more the timing moves.
Off timing can be increased by this progesive curve and might couse the surge.

Did you have the timing checked after the rebuild and gear drive?

Peter

[SteveMc]

Have not had the timing checked by the shop. Have moved it approx two degrees advanced and lowered it in 2 degree increments to about six degress ATDC going by the bench mark at the pump. Made little difference in surge. Did knock more advanced and was harder starting retarded so I think Iam close. Where it is now it starts great and has great power with very little smoke, but the rpm varies at all speeds above 1150. One person I talked with at DSG mentioned the possibility that the internal timing mechinisum of the pump might be off, also something about internal pressures changing the timing. It was beyound me as I have no experance inside a DB2 pump. That may change as I chase down this problem

Thanks for the thoughts.

SteveMc