More Power In a M936A2 - Steel Soldiers::Military Vehicles Supersite

nate_o23 · 05-15-2007, 13:13

Hello all, I am a mechanic in the Army, currently stationed in Iraq. We have a M936A2 with the CTA that is a total dog! We also have an older M923 with the natually asperiated NC 250 and it has more power! The 923 even has the armored cab and turret and it still has more power. Anyone know any tricks or tips to turn up the power on a CTA?? Is there a way to turn up the IP?? Injectors out of a different vehicle?? (like on the HEMMT you can swap injectors out of a M109 for mor power) Anything to get some more power!

WillWagner · 05-15-2007, 13:24

By CTA, do you mean Cummins 6C?

steelsoldiers · 05-15-2007, 13:42

It's the 8.3 CTA Cummins. I know a company called TST performance sells injectors for the 8.3. There are some other performance companies out there since that engine is widely used in trucks, buses, RV's etc... There are adjustments that can be made to the injection pump, but with a truck that big and heavy I would go tinkering with the fuel without an EGT gauge. Is everything OK with the engine? Excessive smoke or oil consumption? Hard starting?

A stock 936A2 weighs in around 37k where a stock 923 weighs around 21.6k so even with the armored cab it may still be about 8k lbs lighter.

jeli · 05-15-2007, 13:48

I'm sure you are aware but 8.3's eat fuel filters in the dust. We were changing them daily in Guatamala. You're also probably running JP8 so depending on how long the truck's been in country any sludge from running #2 will be cleaned out by the JP8. I was about to say who cares about EGT's in your case but JP8 runs hotter anyway so you may want to make sure if you can turn up the pump you don't get too wild. Hate to go down in the middle of a convoy.

nate_o23 · 05-15-2007, 14:06

It just had an annual service and all the filters were changed with no improvement. It doesnt smoke and runs fine, just no nuts, especially off the line. Yeah the wrecker is pretty heavy but it should have more power then this.

The TST injectors sound interesting but I could never get the Army to pay for something like that. If it doesnt have a NSN I cant get it. Same thing goes for the EGT gage.

Not looking for anything crazy, maybe just turn the pump up a little?? Thanks for the ideas & advice, keep it coming!

steelsoldiers · 05-15-2007, 15:16

The 8.3L uses a torque plate like the 12v 5.9L Cummins. Typically you can gain some power by loosening the 2 bolts the hold the plate and sliding it forward. The governor arm rides on this profiled plate and the plate dictates how much fuel the pump will put out based on a given RPM range. Sliding the plate forward will increase fueling in all ranges. It is possible that the 8.3 in your wrecker may have the plate slid back too far from the factory or maybe it is a rebuilt pump and it was set back for a different application. It's hard to say. Either way, sliding the plate forward will give you a power boost and make the smoke roll a little more.

Here's a link to a PDF on ther TST site detailing how to install their Power Kit: http://www.tstproducts.com/INSRUCT98.pdf The pics show a 5.9L setup but it is similar to the 8.3L. The next step is custom grinding your torque plate.

WillWagner · 05-15-2007, 23:38

If you didn't mess with the pump, ie taking the AFC housing off, 3 things that are very common on the P7100 pumps in both the B and C series. The first and easiest thing to check is the FSOV link and capscrews that hold it to the AFC and governer housing. The bolts come loose and/or fall out and won't let the FSOV pull the lever that pulls the rack to full fuel, symptom, low power and sometimes hard to start, depending on how loose the bolts are. Check the link on the FSOV..fuel shut off valve...if it's the older small type, apx 1.5" dia and 2.5" tall, the link breaks in the middle, again, symptoms are low power and sometimes hard/no start. 2nd, the overflow valve at the fuel pump outlet, or return. This valve is a spring loaded check valve. It holds the low pressure that the lift pump makes in the gallery of the P7100. If you don't make the correct ammount of low pressure fuel, the high pressure won't be right. Symptoms, low power, slow acceleration, sometimes white smoke at higher RPM, hard starting. The gallery pressure should be apx 25 PSI at idle, 32+, high idle, no load for a good valve. If you have no way to check pressure, just change it. It's very easy to change. 3rd, the AFC line from the intake manifold connection to the top/rear of the fuel pump. The fittings work loose, wallow the steel fitting and bung in the housing and make it so the AFC can't respond to the manifold pressure, ...it vents manifold pressure to atmosphere instead of letting the pressure push on the AFC diaphragm. Symptoms, just plain low/no power and slow acceleration. I can probably scan some manuals to show you what to look at. PM me if you need pics. Good luck, try to keep us posted. Stay safe and THANK YOU!

emmado22 · 05-16-2007, 08:33

Do whats I did in the Army.... Order a new engine in the can..................

steelsoldiers · 05-16-2007, 11:46

Good tech info Will. You can also remove the plug in the top of the AFC housing and adjust the top of the star wheel inside the housing toward the engine. This will loosen the tension on the AFC spring and allow more fueling at lower boost pressures.

nate_o23 · 05-16-2007, 12:06

Thanks guys, those are some excellent ideas. Unfortunaltely I didnt have much time to work on the wrecker today, we had a M1114 gun truck come in and that took priority. I should have some time tomorrow to check the IP a little better. Ill keep you posted on what I find. Thanks again, this is a GREAT site!

Ill try to post a pic of "Le Beastia" hope it works