Running on 7 cylinders, could PWM be the culprit??

Mr Gadgets · Post by **Mr Gadgets** » Tue Aug 22, 2006 7:58 pm

MSII, V2.35, V3 pcb, MT2.25, 565" BBC, Low Z injectors. Using PWM to fire the injectors. The motor seems to run fine. Datalog shows 12.2-12.6 AFR.. Problem is the motor wont rev past 5100rpm with a load on it.. This motor is in a boat.. I ran 700rpm faster last year than I am now. Made improvements to heads, cam and ignition. I should be able to see 6000rpm the way I am setup. It looks to me like I am running on 7 cylinders. I pulled the plugs and find #5 very white.. also #1 has a white streak across the porcelin. I did a compression check and all cylinders are equal at 135lbs.. Lift on cam looks good.

I am wondering if the PWM circuit is causing one injector or two to not completely open?? I check the operation of the injector, it is opening when 12v are applied and it is clean. I cant test for flow, but I suspect that no fuel is flowing to #5 cylinder.. I have attached a pic of the plugs..

Any input would be appreciated..

Thanks
Dick

MustangSix · Post by **MustangSix** » Wed Aug 23, 2006 11:07 am

Some injectors have a screen inside as a final effort fuel filter. If this is clogged, the injector could pulse, but nothing will get thru. However, I would also troubleshoot the injector harness to make sure that particular injector is getting a signal. A resistor and LED are all you need.

Mr Gadgets · Post by **Mr Gadgets** » Thu Aug 24, 2006 6:02 am

Thanks Mustang,
I pulled the injector and cleaned it.. no dirt or anything to plug it. I will try the LED..
I have since switched my outputs over to Peek & Hold drivers to eliminate the PWM circuit.. Hoping to fired the motor today and see what happens..

Thanks
Dick

Mr Gadgets · Post by **Mr Gadgets** » Thu Aug 24, 2006 5:56 pm

Well I fired the motor with the new injector drivers and ran it for a few mins.. pulled #5 and it started showing some color. Although I had to build a new harness to individually wire each injector, I checked the old injector wiring harness for opens and it seems fine!! I built an injector tester as you suggested, but didnt try it out yet. At the end of the test session, I had color on all plugs. I am led to believe that something about the Holley injectors didnt agree with the PWM circuit. I did have set to 35% and 1.3ms open time.

Then I noticed I had damaged a chip on the CPU board. I have another coming tomorrow..

I will investigate further. Thanks for you input.

Dick