Engine/Transmission (1994 - 1998) 94 Engine Problem(s) - Looking for Feedback

[ihegdal]

I have a 1994 160 hp auto with a little over 81 K miles. transmission is a 2002 ATS and the pump was tuned up in 2004 at PDR. The vehicle is a Scotty motorhome so it doesn't get driven regularly. I started it up for the first time in a couple of months Thursday evening without any problem, idled it at 1000 rpm until up to temp and shut it down. Started it again Friday morning without problem hooked up trailer drove around the yard a little, left it idling at 1000 rpm while loading stuff. I heard the fan clutch kick in a couple of times and still had a bunch of things to do before leaving town so I shut the engine off. When I attempted to start it up about 30 minutes later it would not fire. I ended up loosening the air charge tube at the feedhorn and squirting WD-40 in, engine fired. Had to do this a couple of times before it would stay running. This is problem #1.



Problem #2 and maybe #3 is an intermittent "miss" and unresponsive throttle, I am thinking these two symptoms may be related. I may drive 60 miles with the engine running perfectly and then there is what I would call a 2 - 20 second interval when I think the engine is only firing on 5 cylinders. This will repeat every 10 - 20 seconds. While the engine is in one of these "miss" intervals the throttle is much harder to push and when pushed may not result in any change in power, and if I let off the throttle the engine continues at about the same power level until the miss stops, at which time the engine immediately idles down. This may go on for 10 - 50 miles and then clear up for 10 - 50 miles. The problem does seem to start most often when getting into the power on a hill. The miss sounds a little like a engine with a bad exhaust gasket. The boost will drop 6 - 10 psi depending on power level, say from 19 down to 12 or along those lines.



My guess on problem #1 is a weak/dying lift pump, does anybody have a strong opinion otherwise?



My guess on problem 2 (and maybe #3) is either a problem with a delivery valve not delivering or an injector not injecting. Has anybody had similar sounding symptoms? Could/Can a malfunctioning delivery valve or injector cause the rack in a P pump to stick?



Is there another P pump failure mode that can cause these symptoms?

 

[hsmith]

Seeing you are in the cold country you need to look at fuel gelling and or filter restriction. These lift pumps and the P7100 are very reliable for a long time.

 

[BigPapa]

When's the last time you changed the fuel filter?



Scott

 

[ihegdal]

The temps this weekend were in the +20's and I am using same fuel as my daily driver that ran fine at -50 this winter. Fuel filter is changed each summer. Fuel gelling / fuel starvation has a different feel than what I am currently seeing.

 

[Missouri Mule]

Seems your injector pump/governor springs are acting up.



You can do a fuel pressure test to see if the lift pump is working ( squeeze the return line (rubber) if pressure goes up its the overflow valve if pressure stays the same or goes up slow it's the lift pump.



If it feels like it running on 5 cylinders you could have a injector plugged/not working but the pedal being hard points to the p7100.

 

[ihegdal]

Missouri, Thanks for the fuel pressure check tip. Its easy to do and easy to understand once somebody explains it.

 

[Missouri Mule]

Your welcome!

 

[Gene Heck]

If your motorhome has a fuel shutdown solenoid like the 94-98 pickups do, check to see that it is pulling up all the way when you are trying to start it. If you have a sticking solenoid or the fuel shutdown relay is going bad and not letting the solenoid pull the engine stop to the run position all the way you can get some of the symptoms you described. The next time it gets to running rough after a few miles, don't shut it off and get out and see if the solenoid is open all the way. It could be something as simple as a loose plug or wire going to the solenoid. You can put your finger under the solenoid and pull up on it if it isn't fully open. The solenoid is really two coils in one, the first draws high amps to open it and the second smaller coil is just a holding coil. If the relay is going bad it won't open at all or just enough to give it a small amount of fuel to start and run on but not enough fuel will get into the pump to make much power.



Another thought, while your getting dirty check for leaks in your fuel lines. Usually this causes a hard start problem after setting overnight. It lets air into the fuel lines permitting the fuel lines to empty their fuel back into the tank. Doesn't necessarily show as a wet leak on the outside of the fuel line. Yours is getting the age on it now to start showing these kinds of nuisance problems.



Be careful about shooting WD40 or other flammable things down your intake onto the grid heaters. You might get a little surprise.



Gene

 

[MMcCallie]

You said you don't drive the vehicle very often. How old is that fuel? Diesel can't sit as long as gasoline. My first thought was the fuel filter as others have already mentioned. When you change it, look at the fuel that comes out. Look to see how dark it is, and for debris or sludge of any sort. Try some Diesel 911, Redline additive, or something made to kill bacteria like for a marine application. I would use a lot of Power Service. It may take a few tanks to be running on clean fuel so carry some extra fuel filters in case you have to change on the road.

There are starting fluids that are supposed to be compatible with diesels. I'd use one of those instead of WD-40. And I'd make that a last resort to get it started. Try pumping the diaphragm on the lift pump next time it won't start. Pump until you hear a faint, high pitch whistle coming from the top front of the P7100. Also as previously mentioned, if the fuel shutoff solenoid is not giving you full fuel, your symptoms could be a match.

The clutch normally cycles so the fan engages during startup. It should only cycle after that if the engine temperature has risen. A stiff throttle pedal can also be the result of moisture in the throttle cable that freezes while driving down the road, very scary, but not likely from what you've described. If you are in an extremely cold environment, I recommend a fuel filter heater, especially if the fuel gels in the filter. It doesn't sound like you have any internal problems, probably just a fueling issue.

 

[ihegdal]

I am now thinking there may be some fuel waxing issues. One puzzle I still have is the starting when hot. I drove it Sunday for about 170 miles, ran almost perfectly, one instance of a mild miss at about 115 miles for about 10 seconds. Shut engine off and tried to restart about 30 minutes later, no joy. Tried it a couple of times, cranked fast but no fire. Came back about 2 hrs later and it fire the instant the key turned. I have made arrangements to put it in a shop to warm up later this week.

 

[Gene Heck]

Not to beat the solenoid thing to death but if your out again and it doesn't start like you just described after a run and setting 30 minutes etc. check this,



If you have someone to crank the engine for you get out and watch the shutdown solenoid in action. When they turn the key from off to start the plunger in the shutdown solenoid should pull up (in). This opens the fuel valve in the pump. If you don't see the solenoid plunger pull up you should be able to do it manually with your hand with the key in the start or run position and the secondary holding coil should hold it up. If you have to you can wire it up open with a piece of wire or coathanger or whatever is handy to get you going. Of course, to stop the engine you will have to remove your handywork. As I said in a previous post about the relay you could also have the plunger "gummy" and sticking especially if you have a bad boot on the solenoid. You can disassemble the solenoid and clean this if this is the case and be good as new. A new solenoid is about 175. 00 or so.



At least this will pretty much rule out this as a possibility.



I hope this helps.



Gene

 

[ihegdal]

Thanks Gene, I'll take a close look at the solenoid it this happens again.

 

[ramdriver15]

not to be a smarty pants but the shut off solenoid only pulls up when the key activates the starter.



there is two controlling relays, a pull and a hold relay.....

 

[Gene Heck]

Ramdriver,



I'm not sure how his is wired up since it is a motorhome by another manufacturer and not a Dodge pickup but if you check your service manual you will see that the holding part (low current run winding) of the shutdown solenoid is powered from the same circuit that supplys power to the fuel heater. It is always energized when the key is in the run or start position. No relay for this is required.



The start part (high current start winding) of the shutdown solenoid is powered by the fuel shutdown relay mounted next to the master cylinder. This fuel shutdown relay is triggered (closed) by the starter solenoid when you turn the key to start and the high amp side of the shutdown solenoid gets enough current to pull the fuel stop lever on the injection pump on (up). As soon as the ignition switch is released from start to run this shutdown relay becomes de-energized. This part off the shutdown solenoid (high current start winding) is not powered during normal running. The hold part (low current run winding) of the shutdown solenoid is energized as long as the engine is running and the solenoid plunger is held up. When you want to stop the engine turning off the ignition turns off this circuit de-energizing the shutdown solenoid causing the fuel lever in the injection pump to go to the closed position (down) shutting off fuel to the injection pump.



Calling the fuel shutdown relay a "shutdown" relay is a misnomer. It doesn't shut down anything. It is called that I guess because it directly feeds the shutdown solenoid which always extends when de-energized shutting off the fuel to the injection pump. It is actually a start relay used to help pull the shutdown solenoid plunger in enabling the engine to start only when the key is in the start position. It is not used for any reason other than that.

 

[ihegdal]

Thanks Gene for the explanation.

 

[ramdriver15]

not arguning with you, but from my knowledge and actusl experience that is what i found.



there is a relay that pulls the solenoid up with the starter engagement, and then a hold relay to keep from the truck shuting down. there are two relays. Now on a 96 and up i know this is true, anything prior may be different but i do believe that it takes the engagement of the starter to allow the relay to be energized to pull up.....

 

[Gene Heck]

Ramdriver,



I'm not trying to argue with you either.



If you have a 96 service manual look at pages 8-30-12 and 8-30-47.



If you have a 97 service manual look at pages 8-10-10 and 8-30-24.



They clearly show how the circuit works for the shutdown solenoid. The start and the run circuits. Sorry but there just isn't any holding relay for the "stay" running side of the shut down solenoid. It is wired direct from the ignition switch (start and run positions) through fuse number 9 and feeds both the fuel heater coil and run side coil (winding) of the shutdown solenoid.



Gene