How much fuel pressure......

[bmoeller]

... ... on a 430hp, C-12 Cat?



I suspect we may have fuel injector problem on one cylinder, but want to rule all of the other possibilities first. Truck has 2 fuel filters. First one is a water/fuel separator filter that is on the frame rail. Other, is the one on the engine itself. Both were replaced recently. It did help the engine run a bit smoother, and the boost came back up a little (as did some of the power), but still doesn't feel up to snuff. More in the 1000-1400 rpm range. Not noticeable so much empty or bobtail, but feel it going through town loaded and while upshifting.



What, if any, is the recommendation to replace the vibration dampener? Have ~413k on the truck. IIRC, Cummins suggests a new damper on the N-14/855 @ 380k, and John Deere recommends 5yr/5000hrs on most of their engines.



At first, it was bad enough to make whichever hand was on the steering wheel feel a bit numb before the new fuel filters. Not that bad anymore.



We do have an OEM fuel restriction gauge, but it has always been below 5" restriction, at least for the filter on the engine. No gauge for the water/separator filter. No pyro, either.



Any help would be appreciated.

 

[tgee]

Pretty sure the vibration damper, if its a fluid type, is usually replaced if it's damaged, dented,et'c. If the crank ever broke, it's recommended you replace it. Some mfrs recommend replacing it with an out of frame major overhaul. I think Cats spec for fuel restriction is 6" hg max. Iv'e seen 90 psi fuel pressure at no load speed, which is good. Is it running rough? Low power? All of a sudden, or gradually?

 

[MMiller]

I don't know so much about truck engines, but a c12 in a challenger tractor will throw a check engine light if the fuel pressure is lower then spec. Usually before the tractor has any low power complaint. On the late model engine like yours Brian, fuel pressure should probably be at least 70 psi, and regulated to 100 psi max. I think somewhere under 70 is where the check engine light comes on in a tractor. I know in truck applications the ECM does not always monitor fuel pressure. Go figure.



Sounds like you need to maybe hook it up to Cat ET and do a cylinder cutout test. When was the last time the valve covers were off for a valve adjust? I believe the injectors in that engine are helped with rocker arms too, and need adjustment. When are you bringing it out?



Can't help with the dampner.



Michael

 

[bmoeller]

I know in truck applications the ECM does not always monitor fuel pressure. Go figure.

That I don't know. Unless I've overlooked it, I have noticed a seperate sensor to pickup fuel pressure. If it was low enough to where it should've set off a light or buzzer, it didn't. Seems like it should, particularly with these expensive injectors. I may add a gauge for it, and a pyro, if the boss will let me.

Sounds like you need to maybe hook it up to Cat ET and do a cylinder cutout test. When was the last time the valve covers were off for a valve adjust? I believe the injectors in that engine are helped with rocker arms too, and need adjustment. When are you bringing it out?



Michael

The cutout test came to mind as well. A friend of my boss runs a big truck repair shop, and had worked on the truck when it was being rebuilt. Was told the overhead had been run. Hopefully he has a laptop to do the cyl. cutout test, too.

I think Cats spec for fuel restriction is 6" hg max. Is it running rough? Low power? All of a sudden, or gradually?

I've seen up to 5" on the guage in the winter when the fuel is cold (under 15* ambient temp), but comes down once the fuel warms up. Normally in the 1-3 range. Would the gauge read higher if the water/fuel sep. filter was plugged, since it is before the secondary filter, where the sensor is? I suspect not, since the truck ran much better after the filter change. Before I changed out the filters it felt a bit low on power (and this showed up gradually over 2 weeks), but feels fine now. Was on I-44 in MO Monday night, which is plastered with hills, and it pulled the like nothing was behind me.





Thanks guys. I have something to go by now. I have a 100# gauge in my box. I'll check it out. Don't know if I'll have time this week to check it, or not. Busy week.

 

[MMiller]

Do you have a long hose, and a STOR boss fitting(a fitting with an oring around it)? You should be able to check fuel pressure on the engine, after its filtered, on the filter base. I hope you have a hose long enough to run it in the cab, and start up looking at it. It may well max out your 100 psi gauge on startup, before the valve regulates. I know my boss gets a little cranky when one of my gauges goes all the way around and sticks. :-laf You will probably want to watch the gauge and be ready to shut it off if pressure gets over 100 to try and save you gauge.



Michael

 

[tgee]

Yes, the restriction gauge would read higher if the filter is plugged. It's the reason it's there',to tell you your filter needs changing. Most gauges I've seen have a redline, above 6"hg. I believe on road Cats dont read fuel pressure, but do read fuel temp. That is probably the sensor you see.

 

[bmoeller]

I'm surprised the guage didn't read higher then. There is a redline on the guage, but it is at 10". I thought that was a bit high, that's why I asked. I do know there was some water in the clear plastic bowl on the bottom of the w/f sep. filter, that had to be drained.



Michael, the truck does have the fitting on it, but I don't have a coupler to fit it. I can get a bigger gauge, if need be. No problem there. Do have plenty of line on the guage.

 

[MMiller]

The test port is pretty generic, many companies use them, I wonder if your John Deere dealer would have the female quick coupler for you. I have several of the females on my truck, and Cat sells them. To be safe I'd hook up a 150 psi gauge, just so the needle does not get stuck on the wrong side of zero.



Michael

 

[bmoeller]

That is a thought. I know Deere uses the same type of fittings. I can check. A 150# gauge would be a good idea.