Higher RPM Miss when underhood temp warm - Diesel Forum

danobee · 05-28-2006, 07:09 PM

Can anyone relate to these symptoms. 93 F-350 120K miles, changed fuel tanks and fuel lines last fall due to northeast salt rust problems, external leaks. After this, truck would develop a skip at rpm above 2000 depending on apparrent underhood temp. After cold start, starts fine, runs strong, no skips. If regular driving in winter cold temps no skips, no problems. Start plowing snow, engine coolant temp gauge stays normal, underhood temp hotter because of low speeds, engine starts skipping when asked for power, blue smoke. Take it down the highway, underhood temp goes down, coolant temp gauge stays in same range, but skips and blue smoke go away. When temps are below zero in winter issue never occurs except when plowing. The warmer the weather, the quicker it shows up after a cold start. Have changed fuel filter 2 times, no difference observed. Clear line at filter return shows no air intrusion. Is it possible the injection pump is getting tired and when hot it can't make the pressure to pop the injectors, thus causing skip when underhood temp (corresponding to IP temp?) is hot. Any suggestions for confirming tests before a pump changeout.

cdnsarguy · 05-29-2006, 04:26 AM

Check the lift pump...

Do a pressure and flow test of the fuel pump at the Schrader valve on the filter header (FSS- fuel shutoff solenoid disconnected on IP). Remove the tire valve core and hook a hose and pressure guage on it should see 4-6 psi when cranking. Then do a fuel quantity test same place, should see 1/3 pint in 10 seconds of engine cranking, route fuel to a suitable container with a hose.

If there is a problem with the lift pump and you are changing it, ensure the new pump comes with instructions as to correct installation procedure if it is the newer model pump with the almost straight arm.

Is this problem relative to both tanks when either is selected...

FraserScott · 05-29-2006, 04:41 PM

The advance piston in the injection pump is shot. The piston and the bore which your piston rides develops scores over many miles and fuel just bypasses it. Therefore not working as it should. If you look at your injection pump, and look on the drivers side of it, you will see a lever running in a vertical position. At the bottom of this lever you will see a little plunger which the lever pushes on. With the engine idling, take a long screwdriver and depress the lever so that it pushes the plunger in. Once it is pushed in, idling engine sound should change because you are changing the timing. If the idling engine sound doesn't change this means that that timing advance is worn out and the pump needs to be exchanged. I had the same trouble 2500kms ago, engine would miss above 2000 rpms with large amounts of blue smoke. A reman pump $487 canadian, 8 reman injectors $28 each canadian, and a new lift pump $32 canadian fixed my problem. All parts came from the International dealer because their parts were comparitive in price to others and held a one year warranty. In my opinion, I would avoid e-bay pumps. I had to take my first pump back on warranty within 800 kms because the truck would have trouble starting when hot. They exchanged it no questions asked, try doing that with e-bay ! My truck now runs like dream, no smoke at all and it smells clean with tons of power.

danobee · 05-29-2006, 09:08 PM

This occurs when either tank is selected.

Thanks to cdnsarguy and caterpillar 112 for responding

I will try both recommended tests later this week.

Are the lift pumps marginal in these trucks? What is the benefit to retrofitting a Holley or Mallory electric pump? More flow or instant pressure when the key is turned on rather than cranking to build pressure?

cdnsarguy · 05-30-2006, 12:39 AM

The manual lift pumps put the required amount of fuel to the IP.....

Carter pump #M60278
Pressure Rating: 4 lb - 6 lb
Gallons Per Hour: 23

A Holley will pump 70GPH at 5-7PSI, that's ok if you like to filter your fuel all day for no reason........

danobee · 06-03-2006, 10:29 PM

Saturday night, working on the truck. Performed lift pump tests. Removed the valve core from the schrader valve and installed a 0-15 psi test gauge. Disconneted FSS terminal on top of injection pump so engine wouldn't start. Cranking engine pressure on gauge stays between 4.5 and 5.5 psi at all times. Reconnected FSS ternimal, started engine, 4.5 psi steady with truck at idle, doesn't seem to change much with engine rpm when rpm raised. Removed gauge, clear line into wife's glass measuring cup from the kitchen, and exactly one pint in 22 seconds. Lift pump seems to be doing its job OK.

With engine running just after a cold start I diconnected the cold timing advance solenoid and can clearly hear a change in engine tone when the terminal is connected and disconnected.

As far as Caterpillar 112's suggestion to actuate the lever and piston on the lower drivers side of the IP, I'm not sure exactly what this should do but I tried it. With engine at idle, actuated piston behind lever by hand with a screwdriver. As soon as piston is moved engine tone changes, any move more than 1/8" seems like it will stall engine from idle.

I guess I'm going to change the IP as it seems to be the likely culprit, it just goes against my style to change out parts without proving them weak or bad first. Any other last minute tips or checks?

cdnsarguy · 06-03-2006, 11:55 PM

Have the IP or injectors been changed before........ what code are the injectors, they should be E code for a non turbo and the IP should be a 5013. Have you tried a healthy dose of fuel additives ie Stanadyne or Power service.

danobee · 06-04-2006, 01:08 AM

I have owned the truck for almost 2 years. Bought it at 108K. The previous owner mentioned he thought the pump was changed several years before, it has a Stanadyne Rebuilt sticker on it. I believe the injectors are original. The info on the pump tag is DB2 5028 1845351 F2TZ9A543C . Is the injector code stamped on the outside of the injector body? They are quite dirty and rusty, I can't find any numbers or letters yet. I gave it a real healthy dose of Power Service last fall, I use it at the normal dose rate through the winter. It didn't seem to change the characteristics any of the skipping once the truck gets hot. The temp gauge never goes above half way and usually runs at about 1/3 scale in the normal range.

FraserScott · 06-04-2006, 09:53 AM

Pushing in the little piston and listening for a change in engine sound is just to tell weather the timing advance is working. If the sound of the engine changes, the timing advance is still working. If the engine sound doesn't change, the advance is worn out. Its only a piston that rotates a cam ring inside the pump to achieve different timing depending on engine rpm. It sounds like yours is working though.

danobee · 06-08-2006, 11:02 AM

Borrowed a loaner IP from a friends truck that was in a minor accident and has been sitting waiting for him to get around to repairs. Installed replacement pump and been running the truck the past few days with no skipping or blue smoke issues. The truck idle and throttle response is much crisper. It appears that the IP was the major source of the running problems. Now I'll have to decide what to get for a replacement IP and probably do injectors at the same time. Thanks all for the help.