Natural Gas Engine

[Danandersen]

Hi guys,

I have a Natural gas engine made by Waukesh that keeps detonating.

I have tried cleaning and regapping the sparks this didn't help. I then replaced the sparks and the engine ran good for about 500 hrs. then it started detonating again - I found
a sticky valve on cylinder #2 so I replaced the head, now, about 1000 hrs down the road the engine is detonating again. I have checked my valve gaps, check O2 checked my carbs,
checked the intake temps and jacket temps all looks fine. with the one exception that when this is happening, the intake manifold pressure increases by 2 lbs.

Any thoughts?

Thanks guys.

 

[Lou Scannon]

Your best bet is to get and follow the operator's manual from Waukesha. If that doesn't get you to the bottom of your issue, you should hook up with your nearest dealer.
Intake manifold pressure could be your issue though. I suggest checking that everything playing a role in this... throttle, wastegate, air bypass (if present).
Is there an electronic control? If so, is it trying to tell you anything... e.g. check engine light?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[Danandersen]

Hemi,

Yeah, my book just says to clean and regap the plugs - it didnt change anything, but changing out the plugs cleared the fault.
Throttle and wastegate are all operating as they should - throttle is electronically controlled while the wastegate is mechanically.
I get no check engine lights or anything. This is a big 18 liter generator, all I see is that it jumps around on its skid and the Hz fluctuates a bit, but not much.

It seems that changing the plugs usually helps - this is the third time I had to do it and it cleared the fault, but the plugs only get about 500hrs on them while rated to 1400 hrs.

My dealer doesn't really understand why that is and neither do I.

 

[MikeHalloran]

Can you do a compression and/or leakdown check?

The occasional severe misfire suggests perhaps you have more sticky or leaky valves.



Mike Halloran
Pembroke Pines, FL, USA

 

[EdStainless]

Are you really sure that they are the correct plugs? You may need a slightly 'colder' plug in the same family.
You need to check the detail part number.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Lou Scannon]

On a stoichiometric (lambda = 1) engine, intake manifold pressure increasing by 2psi accompanied by knock is an indication that the control of the charge pressure is being driven upward (either within or outside of the control system's authority) for some reason, while AFR is being held constant at lambda = 1 (as it should be at all times). Stoich, or "rich burn" engines, (lambda = 1), as they are known colloquially in the industry, are always on the ragged edge of knock when at high load, so a 2psi increase in manifold pressure above normal is bound to be accompanied by knock, whatever the reason for the manifold pressure increase. This is what you need to investigate and resolve. For instance, whatever the reason, an increase in compressor inlet temperature, with the control system trying to maintain constant engine power hence constant charge mass flow, will typically result in a collateral increase in intake manifold pressure, within the control system's authority to orchestrate such an increase. All things being equal, the resulting abnormal operating point will most likely push combustion closer to or into knock, for reasons that we can get into if necessary.
Another possibility, for instance, is that one cylinder is dying off at high load (i.e. ignition issue), and the control is increasing charge pressure in order to maintain the same output distributed among the remaining cylinders that are still functioning properly. As above, this will push the combustion closer to/into knock.
Just some ideas. The reality is probably something else. 

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[gruntguru]

If new plugs fixes the problem it is worth checking the ignition reserve. Not sure what the recommended procedure is - if you can't find one try cranking with a modified spark plug (about 20mm gap) on the end of each HT lead. You are looking for adequate a) coil output voltage and b) insulation all the way to each plug.

je suis charlie

 

[TheBlacksmith]

One of my rules of thumb, for what it's worth; if the thing (engine, cable box, etc.) changes its behavior, for the better or worse, right after you touch something, that something is a likely suspect. In this case, since NEW plugs fix it for 500 hours. Then either the wrong heat range or a weak ignition soon causes a problem again.

 

[Danandersen]

For the first time in my 5 years dealing with Waukesha Engines I actually found a legit Tech support team with WPI -

I described my problem and I was told to check for "weak Ignition" as Theblacksmith says. They were pretty certain it had nothing to do with the plugs that I use at all.

I am supposed to check the resistance in each coil and I am supposed to check for 140-160 VDC on the G-lead coming off the ignition module - this should tell me if my ignition module is bad or if
I have a bad coil.

 

[utkuselamoglu]

weak ignition causes that problem.