Stupid Question about a Cummins ISB

Before boosting the fuel system I'd go over all the basics to be sure everything is working properly. Check the charge air cooler & hoses for leaks. Check the waste gate capsule for leakage. Some engines had the waste gate line coupled to the air fuel valve on top of the governor. When the waste gate capsule leaks the air fuel valve doesn't see any boost. Check throttle travel & be sure the stop is going into full run.

 

Have you had the overhead done? I have a 12 valve in my daily driver and I was amazed at how much get-up-and-go was restored after I had the overhead done.

Has your 24 valve been p-pumped or is it still running a VP44? If it has a p-pump you can tune the star wheel and the smoke screw to get more power out of it without it being a heavy smoker.

You may want to advance the pump timing a little bit. And if you go for the bigger governor springs talk with an engine builder to make sure your engine can handle the increased RPMs on stock valve springs.

 

We had a ‘95 F800 24’ box truck with a mechanical 215 hp 5.9 6-speed Spicer 4.33 rears and 11r22.5’s. We ran South Texas valley and coastal bend with it. The winds we get down here killed it. Back when Texas speed limit was 55-60 it would get 62mph if pushed hard with palm of hand pushing knee cap into leg harder down on to the peddle. Lol! Hauling 26,000 gross at 220,000 miles and she was wore out. Without those 4:33’s I’m sure she would not move.

Much to small of an engine for a medium duty truck that does mostly highway miles. Great for vocational and local short hauls.

Can’t remember any major problems with it other then we had a few fuel pump issues and they were known for cracking the timing case cover in the Fords back then. So check that for sure. We had ours replaced twice over a 6 year period.
Never replaced clutch,driveline,or brakes in that time and were still good at trade-in.

 

Killer dowel pin. The gear case has to be aligned to the block perfectly, because engine timing depends on it. One of the dowels would squirt out of the block after so many heat cycles, and fall on the gear train. The gear would drag it against the gear case and crack it. You can fix it without pulling the cam, but back when it was a hot issue, most people didn't know that, so it was a pretty big job. That dowel has to be tabbed to prevent it from happening.

P7100 is super easy to wake up. After that, just add air as needed. A good stop gap was to create a hybrid turbo from an HX35 and an HX40. You get the benefits of quick spool and stronger shaft from the 35, and the increased air from the 40's impeller. Keep you running until you got hot enough to need an actual turbo upgrade. Super fun engine to mess with.

 

Just to add to what you mentioned in the operating range. It would not pull any kind of weight below 1800 and 2700 rpm is what it needs to maintain hwy speed. Ours ran that everyday all day and I believe that is what wore it out. Anything higher then that will probably hurt it worse. Like I said not enough engine for what we were asking it to do. It was very stressful running mashed into the governor 99% of the time while screaming at it. Lmao!

 

Thanks for that explaination.
The first one that was replaced was when still under warranty. Grande Ford did it and at the time San Antionio/Bexar co. CPS had a fleet of them and we had to wait a month for the parts to get in for the fix because they had a couple dozen others in line.
On the second one Grande had Cummins Southern Plains do it for them.

 

I put a '97 in my '93 Chevy. It had 227k on the engine when I bought it. I tabbed the KDP first thing. It was already sticking a quarter inch out of the gear cover. For reference, it's supposed to be about an eighth inch RECESSED. So it had already moved 3/8". That issue was certainly a "when not if" situation.

Those pumps generally defuel around 2,200 RPM. A 4k governor spring kit wakes them up like no other. Literally has the throttle response of a hopped up small block. And you can take a 12-valve to 4,800 RPM safely as long as you have valve springs and push rods to back it up. The crank could take it. Harmonic destruction was around 5,400 RPM without balancing.

I love them because of the platform to tinker. You've got a bottom end that can handle 1,000 horsepower stock, and a fuel injection pump from a 14-liter engine. Couple tweaks, and you could make gobs of power. After I got mine up and running, I did what we called the "free mods", which was just grinding the AFC foot for full travel, sliding the plate, stuff like that. Made 359/831 on the dyno my first try. You could make it outgrow the stock turbo without even throwing injectors at it. When it was said and done, I was running an HE351cw from a 5.9 Commonrail, over an HT4c from an N14 Cummins. 2,400 CFM and 80 pounds boost, and I'm not joking, in the circles I ran, I had the "mildest" truck.