Engine/Transmission (1994 - 1998) Need Help with 96 12V with Major Fuel Problems

[dieselfab618]

Got a 96 12V, just stock besides some 40hp injectors. Its been low on power, slow reving, white smoke, and its back fired a couple of times out the exhaust. Finally put a fuel gauge on the filter housing and inlet of p7100 and its reading 3 psi at idle and once I finally get it up to 2500 its 15 or so.



I have replaced the overflow valve, supply pump, cleaned the strainer filter, replaced fuel filter and nothing is helping the pressure at all. I can clamp off the return line some and it will go to 50-60 psi but still seems to run horrible with tons of white smoke at 2000 rpm or more and smells like raw fuel or i guess lack of fuel???



I have also dropped the tank to check the intank filter and just to see if there is a restriction there. I also took off the small rubber elbow from the strainer to the supply pump and hooked a hose directly to the supply pump and then to a bucket of diesel and not a difference.



I am out of ideas and have research and research and don't know what else to do and check?



I need help to get this truck up and running.



Thanks

 

[CCiatteo]

Is it tough to start, or starts ok, just runs like pooh? Does it idle? Smoke at idle? How did these problems come about? Was it good one day and horrible the next? Did the truck sit for some time? What about the two rubber fuel lines from the chassis to the motor, located up on top of the bellhousing/transmission at the driver side rear of the motor?

I just worked on my fuel system this weekend and you seem to have hit on all the common trouble spots, but I am not an expert. Could pump timing be out of whack?

 

[dieselfab618]

Starts easy and it will drive just low power and white smoke. Idles fine and it smokes just a little at idle. Truck has 200k on it and has been driven everyday and just started getting worse and worse. If I did the pickup from a bucket of diesel straight to the supply pump that would eliminate the rubber lines right? I am going to do timing and check it but want to figure our my fuel issue first... can the timing mess with fuel pressure? Don't see how but never know. Anybody have problems with the camshaft lobe wearing off causing low pressure since the pump doesn't travel far enough???

 

[snappy]

Welcome to the TDR. The cam lobe can be worn, but it is usually caused by improper lift pump installation, such as leaving out a spacer. I have seen this on 5. 9 Cummins that were in medium duty trucks. Never seen it in a Dodge/Cummins combination.

If the lift pump is new and the filter is new and you were taking fuel from a pail, then the lift pump is suspect. There are 2 lines, a supply and return. Timing is a separate issue from fuel pressure. The fuel issue must be solved before doing timing.

 

[CCiatteo]

How about the Fuel shut off solenoid, is it seeing full travel. Is the linkage to the P7100 free and moving freely? Maybe the solenoid/linkage is opening, but sticking and not seeing full travel, so the P7100 isn't seeing full fuel? Might explain the fuel pressure at the P7100 being low? (Not my original thought, just something I read on here at one point or another)

I would agree that if you are pulling fuel from a bucket, then the two rubber lines from the chassis to the engine would be eliminated from the equation. And if the truck is starting ok, then it sounds like it isn't losing prime.

I don't think the timing would directly effect the fuel pressure either.

If the lobe on the camshaft was tore up, I am pretty sure you'd see the debris in the oil. And once the hardened surface was gone, you'd chew through the softer core pretty quick leaving you with no fuel pressure at all probably, just like a lifter chews through a cam lobe pretty quick and you loose valve lift. You could pull the pump again and have a look.

If you suspect the transfer pump, there is a volume test you can run. I think you disconnect the line to the filter head and crank the engine for 30 seconds, then based on the volume transfered, you can determine if the transfer pump is within spec.

 

[fest3er]

If you are getting little fuel pressure normally and lots of pressure when you pinch the return line, the p-pump's overflow valve is bad, misadjusted, or assembled wrong.

White smoke is, of course, unburned fuel. There are three general causes: very early injection (25+ degrees advanced), very late injection, or very cold fuel/air/cylinders. It's probably not cold enough yet. Your p-pump probably is not advanced that much (usually such advances are for drag racing and sled pulling). That leaves late injection, which I might attribute to the p-pump not getting fuel into the barrels fast enough, except the problem should go away when you pinch the return line.

Hmm. Possibly bad pop-off pressure in one or more injectors; too low and you won't get good atomization of the fuel. If you have the old injectors, give 'em a try. Possibly leaky injectors?

Perhaps the injection timing slipped? The shaft and gear must be thoroughly cleaned before assembly.

Is there a charge air restriction? Take the hose off the intake manifold and see if that helps any. Sure, you won't have boost, but unloaded, the engine should run better if there's an instake restriction.

Remember, you need four things for diesel combustion: atomized fuel, air and compression, and fuel injection at nearly the optimum time. If any of those is off, the engine won't run well.

 

[dieselfab618]

If the cam lobe was worn would I see wear on the plunger of the old lift pump also?

 

[snappy]

It will look like normal wear.

 

[dieselfab618]

The plunger on the pump looks fine? Heres a pic of it.....



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This is the old supply pump we took off. . looks normal to me?

 

[gathomas]

Just my two cents - I would make sure I didn't have a Turbo supply air leak, there are several connectors that should be checked, not to mention the air filter, (squirrel nest, rodents. . etc) Do you have a boost guage ??

 

[surfbeetle]

On mine, I had the blue line that attaches to the wastegate elbow on the turbo rub/burn through and leak. When this happens, there is no boost going over to the injection pump to the AFC. Might want to check that.

 

[dieselfab618]

But I am having fuel pressure issues?? nothing to do with boost or the turbo.

 

[surfbeetle]

When you dropped the tank, I am assuming that you inspected the hard lines from the front to the rear, correct? I had a leak on the hard line at the transmission, had to cut it down and put a flare on it before clamping a new line on it. Is the raw fuel smell coming from the exhaust or do you smell it up front? As for the white smoke, often times that is engine oil being burned, diesel smoke tends to be darker. You mentioned backfiring, that could be valves or timing. I have not had that happen on a diesel, but I would think that low fuel would not cause a backfire since it's the increase in amount of fuel that increases engine rpm. When were the valves last adjusted? What's the timing set to on the injection pump? Lastly, was the KDP checked? It can fall out and mess up the cam gear in the front gear case. Also, if you PM JoeG, he can send you the 12 valve fuel system write up that he's been diligently maintaining all of these years.

 

[dieselfab618]

The smoke is like a whitish blue i guess but more white and smells of raw fuel from the exhaust. Usually when the dowel pin falls you can get can't you? Truck runs and idles fine. Just did valves on it about 2 months ago. I got that fuel system run down that JoeG did. There are no fuel leaks anywhere.



I has me puzzled big time... ... .

 

[surfbeetle]

You wrote earlier about the injectors not being stock, have they been tested? Also you can use of those laser thermometers to check cylinder temps to see if one cylinder is not combusting properly. That could indicate a problem in the pump. Just thinking as I write this, but when you pinch off the return line and get higher pressure, that is after the injection pump. I wonder if there's something wrong with the injection pump that is causing most of the fuel to return rather than go to the injectors. Do you have the stock plate in there? Has the AFC Wheel been adjusted or messed with?

 

[dieselfab618]

You wrote earlier about the injectors not being stock, have they been tested? Also you can use of those laser thermometers to check cylinder temps to see if one cylinder is not combusting properly. That could indicate a problem in the pump. Just thinking as I write this, but when you pinch off the return line and get higher pressure, that is after the injection pump. I wonder if there's something wrong with the injection pump that is causing most of the fuel to return rather than go to the injectors. Do you have the stock plate in there? Has the AFC Wheel been adjusted or messed with?

The pump is all stock, I have a fuel pressure gauge at the inlet line on the Injection pump by drilling and tapping the banjo bolt and it says 3 at idle and 15 at 2500RPM.

 

[surfbeetle]

Well, I'm all out of ideas. Sorry I can't be of any further assistance.

 

[dieselfab618]

Thats what I'm afraid of... .

 

[snappy]

It is doubtful that the camshaft lobe is worn down that much to effect fuel pressure. It does happen, but only when a spacer (medium duty applications) is left out during lift pump installation. When this happens there will be other engine damage. The pictures look fine.

The symptoms point to either a bad lift pump or overflow valve.

 

[dieselfab618]

I am going to pump on another new lift pump and overflow valve just to see this morning.