waukesh 7044 gas engine for compression is rpm hunting issue

[prajeesh thomas]

Dear All,
we have an issues in one of the 7044gsi AFR2 gas engine , rpm is hunting , engine running for a while and suddenly rpm dropping then normal it happing continues, we changed and check the following things.

1. Both side wire way and interconnecting harness.

2.IPMD

3.PDB

4.ESM

5.Governor.

6.throttle.

7.both side fisher regulator

8.carburetor diaphragms.

9.checked the cylinder pressure.

10.checked the valve adjustments.

11.spark plugs & ignition coils checked..

12.waste-gate checked.

13.main bearing temperature normal

14. Oil pressure & Temperature normal.

15. Still the issue same. Any suggestions to check other things

 

[hillbilly1]

Probably the wrong forum for that question, but probably a fuel supply issue.

 

[prajeesh thomas]

hi ,
which form i need to discuss?

 

[roger]

This is an electrical forum and even though I think the engine you are talking about is used for generators you probably should be looking for an engine related forum.

Roger

 

[synchro]

Dear All,
we have an issues in one of the 7044gsi AFR2 gas engine , rpm is hunting , engine running for a while and suddenly rpm dropping then normal it happing continues ...

Was this engine and its connected load working properly before, and then RPM started hunting without any changes made in how it is used? If so, then there could be a component failure as you've been trying to identify, or there might be a leak in the intake system that is affecting the fuel-air ratio.

If the engine and its load were not already running well previously, then perhaps the engine controller is not programmed properly for the inertia of the load (e.g., too much loop gain for a low inertia load). Or the load might be cyclic, perhaps even exciting the engine speed control loop near a resonance in its response.

 

[hillbilly1]

As Syncro mentioned, could be a vacuum leak, if it was fuel injected, the computer would try to compensate and cause it to hunt, but since you said it has a carb, that wouldn’t be the issue. Check fuel pressure and delivery system. Could also be a stopped up fuel filter starving the carb when it’s loaded.

 

[prajeesh thomas]

Was this engine and its connected load working properly before, and then RPM started hunting without any changes made in how it is used? If so, then there could be a component failure as you've been trying to identify, or there might be a leak in the intake system that is affecting the fuel-air ratio.

If the engine and its load were not already running well previously, then perhaps the engine controller is not programmed properly for the inertia of the load (e.g., too much loop gain for a low inertia load). Or the load might be cyclic, perhaps even exciting the engine speed control loop near a resonance in its response.

 

[prajeesh thomas]

The engine was working well before the problem start, so engine controller all programmed ok.no electronic component left to replace ,all done, the hunting is not too long if engine is running 1100rpm suddenly drop 200rpm for a fraction of second and to normal this is contionsully happening.
today replaced the power supply module to veryfy any power issue,we are wondering what component creating the issue.

 

[prajeesh thomas]

As Syncro mentioned, could be a vacuum leak, if it was fuel injected, the computer would try to compensate and cause it to hunt, but since you said it has a carb, that wouldn’t be the issue. Check fuel pressure and delivery system. Could also be a stopped up fuel filter starving the carb when it’s loaded.

 

[prajeesh thomas]

the fuel pressure checked its steady 40psi both load and unload. ,during unload time engine working normal without any rpm fluctuation.

 

[hillbilly1]

Doesn’t sound like a fuel issue if that’s what it’s doing. How long is the cycle? A couple of seconds? A minute? Kinda sounds like it’s loosing the rpm sensor. Possibly rust on the magnet on the flywheel?

 

[prajeesh thomas]

Doesn’t sound like a fuel issue if that’s what it’s doing. How long is the cycle? A couple of seconds? A minute? Kinda sounds like it’s loosing the rpm sensor. Possibly rust on the magnet on the flywheel?

 

[prajeesh thomas]

we can say drops rpm a second and back to normal . we replaced the crank sensor , didn't check the flywheel condition.will do this also tomorrow

 

[synchro]

Are any faults stored in the engine control unit?

 

[prajeesh thomas]

Are any faults stored in the engine control unit?

 

[prajeesh thomas]

no fault showing. if run for long time some time hunting the load increased to 105 and throttle open100% rpm drops 1100 to 950.these all happening for a short time. some times its tripping due to overload , or exhaust temperature high

 

[synchro]

The engine was working well before the problem start, so engine controller all programmed ok.no electronic component left to replace ,all done, the hunting is not too long if engine is running 1100rpm suddenly drop 200rpm for a fraction of second and to normal this is contionsully happening.

Can you look at the throttle actuator when the engine is running and observe if if the actuator is moving significantly? If it is moving, check if it looks like the engine RPM drops before the actuator has a chance to move (which might, for example, be due to an ignition dropout). Or does the RPM change as as a result of actuator movement (changing at the same time or slightly after the movement)? That would indicate that the speed control loop is involved in some way with the speed variation.
Also, from an on-line search it appears that you should be able to read the intake manifold pressure on each of the two cylinder banks. It would be good to make sure that the readings are close to each other.

 

[prajeesh thomas]

throttle actuator slight movement during the unload condition, but in load condition the movement is more, first rpm drops ,after that to try to compensate the rpm the throttle opening wide. as you said it due to ignition cut, but there is no change in the spark reference ,if ignition cut for a second the spark reference should change.
the manifold pressure have no significant change ,both bank alsmost equal.

 

[synchro]

Possibly an ignition coil has an intermittent internal short. Typically such shorting occurs on the secondary winding because of the stress from the high voltage. The voltage gets higher when the engine is loaded because it takes more voltage to fire the plug at the resulting higher cylinder pressure, and so the coil is more likely to be breaking down under this condition..

 

[prajeesh thomas]

for this to confirm we already replaced 6 new coil in one bank and next to swap to other bank. same problem, all spark plug also replaced. ignition coil extension also checked.