help with my 2008 isx no start..fuel issue??

[shaneco1]

my isx 15 cm 871 i belive i started it the other day and it just slowly ran out of fuel now wont restart so i changed fuel filters filled new filters,,then changed out fuel stop selanoid,,, found lots of varnish still no start,,,took puck out of stop selanoid no start,,,,put new lift pump on it and replaced 10 amp fuse on the motor no start,,changed out pressure valve by the return line..no start..bought a complet icm i think you call it complete from truck yard with gear fuel pump used ,,installed ..still no start,,put a pressure guage on the fitting up by the gear pump only get 15 psi when pump runs ..then it drops to zero when pump stops,,,shouldnt it hold pressure??? i started it sort of on starting flued.. whith the guage installed on lower test port by the selanoids,,pressure got to 270-285psi when on either then it dyed of course uggg,,i am putting fresh fuel from a 5 gallon can to it for now since i think tank bad,,..maybe fuel passages plugged or??? it was running soo what the haa??need some help to figg it out...

[same101us]

Maybe your vgt turbo is stuck closed

[Rawze]

CM871's are notorious for that "mystery no start" no matter what the h$ell you try scenario. -= Seen a lot of people go crazy over this trying to solve it.


First, it should be known that while electric lift pump is running, pressing in the compu-check test port ... fuel should come blasting out of it. Letting it purge for about 10 seconds usually purges most of the air in the pickup lines etc. -= WASH all the the fuel off the truck and engine with water and soap so that it is not a fire hazard after, if someone does this.

Next.. something else to keep in mind ...

Worst case scenario is during first crank right after an inframe. This would be where everything is bone dry including the insides of the injectors, head, everything. -= After purging the air out of the fuel like mentioned above... It takes a full 30-seconds long cranking session (the ecm/starter will usually time-out) .. then a 10 minute rest to let the starter cool off, and then a second 30-second cranking session during which it will fire off.

Here is a fine example of this in these 2 videos when we did Waterloo's truck here at my house...
first crank attempt: https://youtu.be/PpsfujvFKcM
second crank attempt, and it fires off for the first time: https://youtu.be/1hdRaSD9mqk


-== keeping that info in mind...



Here is what needs to be done for that no-start scenario from he#ll on them ......

A)> while the electric fuel pump is running.. press on the compucheck port .. fuel should come blasting out of it at high force. It also should not be full of air.

B)> Smack the top left corner of the ECM.. almost hard enough to dent its casing... if the electric lift pump cuts out or acts up when you do this.. THE ECM IS BAD!. The CM871 ecm's in particular are notorious for going bad and getting intermittent like this. This especially if the ecm is more than 8+ years old.. OR (more common) if some moron has never changed the crank shaft damper when it was due (according to proper maintenance schedule) ... and the constant engine vibration finally took it out.

B)> Watch the OIL pressure gauge in the dash while cranking. If it does not move a few psi above zero.. even after about 20+ seconds of cranking.. then the ECM IS MOST LIKELY BAD! That or the oil pressure sensor.. or perhaps oil pump itself.. but the most common issue for this .. is a bad ecm actually.


- You say you measured the pressure manually.. but you need to actually do this with the software instead ...

C)> USE the cummins Insite software to monitor fuel pressure while cranking. Insite should report more then 50 psi minimum or the ecm will not even try to fire off the injectors. Just for reference, most trucks will show 100+ psi when they are healthy. This needs to be verified. So if insite is reporting a low fuel pressure during cranking then almost always.. it is the gear pump shaft that has snapped internally.

* It can also be that the fuel shut-off solenoid has gone bad and not allowing fuel ... so removing the guts inside of the fuel shut-off solenoid and doing this check again is necessary before assuming the gear pump has gone bad.

NOTE: Ironically, when the gear pump internal shaft is snapped .. it usually will catch and make full fuel pressure if someone uses starting fluids to start the truck, so it fools you into thinking it is ok once it is up and going .. but it will not make proper pressure while cranking. Hence, using insite to check this. -== this is in fact the most common scenario of all with regard to in not cranking no matter what you try or replace.

D)>. Also make sure there are no crank/cam position faults in the ecm while your at it.

E)>. THE TURBOCHARGER.. as it wears out is known to hang up at 100% position and mechanically get stuck there. -= If it does this then the exhaust manifold will be choked off so hard, that the engine cannot let exhaust gasses out. This causes it to only stumble momentarily sometimes and die.. or simply not start at all ... or to only seem to rev up a few rpm after cranking, and labor against itself really badly. NOTE: The engine will likely also not run (or only run momentarily and die, or have revving up issues) even if you use starting fluids.

-= If the turbo being locked-up at 100% is suspect ... then someone needs to remove the turbo actuator off the top of the turbo and check the VG arm movement to ensure it is free and has full travel range. If it is ok, then an actuator install and calibration procedure needs to be done to get it back on properly.

[RollinCoal]

1 way to tell if turbo is hung is to watch exhuast back pressure while cranking
if turbo is hung it will go way high (50+ psi)
If thats the case back off the turbo mounting nuts and let the turbo drop down to make a gap, it should crank (if the turbo is hung up)

ECM issue
the sweet spot Rawze is talking about is about an inch over from the top left (front of the engine) corner

[shaneco1]

thank you guys need all the help i can get/// friday teck comming up put his code reader on it,,,120 ph$ujgg... going up to it tommorow and try your advise,, will let you know

[shaneco1]

what should be the cranking presure of this isx when the lift pump runs 10 seconds.. it only hits 15 psi.. then drops off to zero ???...

[tree98]

(02-15-2023 )shaneco1 Wrote:  what should be the cranking presure of this isx when the lift pump runs 10 seconds.. it only hits 15 psi.. then drops off to zero ???...

Your posts are kinda hard to make sense of. Are you saying fuel doesn't spray out with any force when you bleed the compucheck fitting while the priming pump is running? If so then you likely have a problem with the priming pump or lines feeding it. Maybe you should go back and read what Rawze posted again.

[Rawze]

(02-16-2023 )tree98 Wrote:  

(02-15-2023 )shaneco1 Wrote:  what should be the cranking presure of this isx when the lift pump runs 10 seconds.. it only hits 15 psi.. then drops off to zero ???...

Your posts are kinda hard to make sense of. Are you saying fuel doesn't spray out with any force when you bleed the compu-check fitting while the priming pump is running? If so then you likely have a problem with the priming pump or lines feeding it. Maybe you should go back and read what Rawze posted again.

I guess you guys did not see the crazy posts that I had to delete from this user, bragging about 650+ HP, to which, as far as I have seen so far ... cummins did not make factory programs for the CM871 in that HP rating. This means that it likely has one of those typical engine destroying delete programs is in it. He also was posting about modified exhaust manifolds, and the fact that it is in an RV (even worse yet due to heat flow restrictions at higher HP ratings ) ... == to me this is all considered nothing but red-neck style engine abuse for a $40,000 commercial engine.

-= Sad part is that it is likely that the guy does not even know any better. They are probably a victim of brainwashing from that garbage can RV community of complete idiots out there who occasionally bleed onto my forum when they get tired of destroying their engine a few times, blaming it on everything but their own abuses.

I muted this person for a while just to keep the trash off the forum here. Maybe this thread will help them with their engine start issues in the mean time... of course, assuming for a moment that the engine's likely idiotic, abusive mods have not caused this grief in some obscure way.