Question for you 1st gen gurus

[Kirwin]

I working on a friends stock 93 4 X 4, Ram 2500 automatic with 175,000 miles on it. Occasionally, for no apparent reason, while idleing the speed of the idle drops so low that the oil pressure light comes on and it nearly stalls. It will continue to idle this way until you step on the gas pedal and then sometimes it will be OK other times it will go right back to the low idle condition. It can sit there and idle for an hour though and the condition doesn't occur. I have replaced the lift pump which was leaking out of the weep hole, replaced the fuel filter, verified that all the high pressure lines are not leaking and that the low pressure supply line is not kinked or otherwise restricted. It appears, as best as I can tell, that it has the original injection pump. As an aside, I checked the grid heater solenoids and one has been very warm in the past. The truck does not seem to me to have much power. You can floor it in gear and it doesn't seem to strain much. I don't drive many stock trucks though so maybe its normal. Any ideas?

 

[cerberusiam]

Possibly a fuel delivery problem, you did the obvious but there are things on these older trucks that you really have to dig for. One really good one is a rubber line deteriorated inside and when higher flow is demand a flap of rubber choking off the flow. Tank module could be a problem also if the line is broke and sucking air or a piece of something plugging the pickup. Fuel shutoff solenoid could be a problem also.



Could just be time for an injection pump rebuild. That would be my first guess with the other symptoms. Do you notice any white smoke out the tail pipe when warm, like accelerating hard? Any white smoke at startup cold? Some is normal but it should clear after about 5 seconds.

 

[Kirwin]

low idle

I haven't started it cold yet so I can't say when cold but no white smoke when warm. Is the shut down solenoid in the VE pump an issue? I hadn't heard of that being an issue on the VE pumps. I thought of the hole in the line somewhere in the suction side of the lift pump but it doesn't act like a dropped cylinder when it occurs which is my experience when the fuel becomes airated. Its almost like you suddenly put a large load on the engine at idle that the injection pump doesn't respond to correct the idle speed. We set the basic idle at 750 RPM A/C on, in drive and it idles there most of the time than all of the sudden it will drop to like 350 RPM out of the blue. Any other ideas on what to check before buying an injection pump? Thanks Ken Irwin

 

[Tippin Spotted Cow]

Does the idle drop when idling with your foot on the brake and the truck in gear only, or does it also happen in neutral and park? I've been battling an issue for a while where the truck idle is always very low when in gear with my foot on the brake (ie a stoplight). If I pop the truck in neutral it evens out, and idles just fine. Or if I leave it running in park... it would idle just fine like that all night. When I take off the thing has no power for a few seconds... which is a new issue that came along with the same problem.



It started out intermittent, like if I was abusing it a little bit... if I did a brake stand or something stupid like that, it would drop the idle and if I tapped the accelerator it would even out. If your symptoms sound any bit similar to this, I believe its a transmission issue. I've been back and forth with the place that rebuilt my transmission because they claim its a lockup torque converter issue... which as you know, the 93 and ealier trucks didn't have lock up. Personally, I believe one of the clutches for a certain gear is getting stuck... like say the truck is shifted into first, but the clutch for second is stuck engaged also. It's a theory and I know about this much --><-- about auto trannies, but just a hunch anyway. Let me know what you find out.

 

[csnider]

Air?. . I'd see about replacing the seal in the quick connect fitting on the lift pump suction side. . also at the tank. that is , if the line itself is still good. do the one at the lift pump first . small square O ring in the female Quick connect fitting, Napa might have something . These early trucks don't like air in the system and it is a good thing to look over the fuel system once in a while. .

I always take the drivers front wheel and shock tower out(4X4) to give a bit of free space to work there. .

The air would be a contributor to the bad performnce and rough idle. . at higher RPMs the return lines are probably purging the air out better than at idle. .

In stock form the 93 auto is not a very powerful feeling truck anyhow. . turning up the pump pressure in the transmission and doing a few very simple things with the injector pump make them much more "snappy"



Of course I would leave the mods out till you're sure you've whipped the problem at hand... .....

Also @ 175000 , there could be injector issues... ... .....

 

[cerberusiam]

I haven't started it cold yet so I can't say when cold but no white smoke when warm. Is the shut down solenoid in the VE pump an issue? I hadn't heard of that being an issue on the VE pumps. I thought of the hole in the line somewhere in the suction side of the lift pump but it doesn't act like a dropped cylinder when it occurs which is my experience when the fuel becomes airated. Its almost like you suddenly put a large load on the engine at idle that the injection pump doesn't respond to correct the idle speed. We set the basic idle at 750 RPM A/C on, in drive and it idles there most of the time than all of the sudden it will drop to like 350 RPM out of the blue. Any other ideas on what to check before buying an injection pump? Thanks Ken Irwin

You could try routing a line from the suction side of the LP to a container of good diesel to rule out the lines and the tank.



The shutoff solenoid has a rubber tip on it that could rip and flap over partially plugging the fuel inlet. Just one of the many weird things that could happen.



Dropping out of idle that far really sounds like the governor is just pulling the fuel back too far. Could try turning the pump up and see what happens. Kick th etiming up and drive the snot out of it. If you have a pump problem at some point it is going to show up as white smoke when warm and a major surge or just cut off when accelerating.

 

[Kirwin]

Still working on it

We have decided to first check the fuel inlet system from the tank to the lift pump. Unfortunately we had just filled it up so I told him to drive it until its empty again and then we'll drop the tank. I'll keep you posted. I told him to also look for white smoke when this occurs to see if its showing white smoke during the low idle conditions. Ken Irwin