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RE: CM870 tuning - Rawze - 06-27-2026
Referring to this post...
(01-13-2024 )DCtruckin Wrote: ...The truck never gets above 850-860 on the pyro, boost is 30psi. CEL is always on
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... and this post ...
(06-26-2026 )Magnat1976 Wrote:(01-15-2024 )tree98 Wrote: Your boost and pyro are both too low. While low boost isn't really harmful, it's just a waste of fuel. The low EGT's could point to trapped heat and higher than normal coolant/oil temp. You need to get this straightened out properly and then you can brag about fuel mileage lol.Hi Tree,I am going to do Running rough tune tomorrow ,you are saying that EGT has to be higher?
I am getting 450,500,600..Pyro probe laid on the exhaust manifold, oil temp 100-102 Celsius
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Here are the numbers to look at for an ISX when the engine is at full max power (100% throttle) output up a long sustained hill climb (several minutes of sustained pulling at max throttle) and heavily loaded down ...
== The EGT's on an ISX, under max load sustained, should be in the range of 1050+F - 1150+F or so post turbo with the probe inside the exhaust pipe, right past the turbo. OR if probe is inside the manifold pre-turbo, It should be about 100F deg or so hotter or so.
== The OIL temps should build more slowly, but should crest at about 230-F, maybe 235-F on the high end.
== The max BOOST (after a de-mandate is done) is different on different year/make model ISX's as they have different compression ratios. Here are the numbers in a sustained pull after a minute or more ...
- ISX CM870 = a sustained 36-38 psi max in a hard pull. Above 38.5 psi is harmful.
- ISX CM871 = a sustained 36-38 psi max in a hard pull. Above 38.5 psi is harmful.
- ISX CM2250 = a sustained 34-36 psi max in a hard pull. Above 37+ psi is harmful.
- ISX CM2350 = a sustained 32-34 psi max in a hard pull. Above 36+ psi is harmful.
- ISX X15 (2350 and 2450) = a sustained 31-33 psi max in a hard pull. Above 34+ psi is harmful.
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That being said.. here are some red flags to look out for... especially if someone has custom (or delete) programming that is not quite right / typically harmful to the engine...
Again, this is at is at full max power (100% throttle) output up a long sustained hill climb (several minutes of sustained pulling at max throttle) and heavily loaded down ...
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== OIL TEMPS climbing too rapidly, or are able to get above 240+F. The most common reason for this is a bad de-mandate program where the engines internal friction is excessive due to wrong operating mode and/or bad injection timing settings, etc.. and the engine is eating its own guts out over time.
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== BOOST is excessive vs. the numbers that I posted above. If its not a de-mandated engine, and EGR is active, then boost levels will be naturally higher (by up to 3-4 psi) due to the added EGR gas going into the intake. If engine is de-mandated, then either the delete program is bad in some way, causing excessive boost, or the turbo settings are too high for the make-model vehicle ... Something is wrong.
== (CM870's in particular) - BOOST spiking to normal levels and then falling off to only 30-32 psi in a long pull. Assuming for a moment that the turbo controller is not acting up ... The most common reason for this is a bad de-mandate program where someone did not shut off the Aux. emissions settings inside the ecm itself properly. This is very common these days, as there are fewer and fewer people who know how to correctly de-mandate a CM870 with all their various programming/ecu quirks.
Excessive boost, especially at high power levels will kill an ISX in a hurry, so it is a very bad thing to see!. More air does NOT mean more power... but only "too lean", and this is extremely harmful to the engine internally.
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== LOW BOOST, especially at high power levels will not hurt the engine but are an indication of something wrong either in the programming, or a mechanical issue that is causing lower than normal boost. It can also be from the ecm limiting fuel (or a mechanical fuel issue). If it is in the ecm, this can be seen by monitoring 'CBL_Fuel_state' along with other settings in the C*Term software when its acting up.
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== LOW EGT"s vs. the numbers and conditions that I posted above (after a de-mandate). - EGT's coming out of the engine are are a tricky one to explain. It is not so straight forward as people think. The issue is that when an engine makes max power output, it makes a lot of combustion heat. All the combustion heat being produced under max load IS GOING SOMEWHERE. WHERE IT IS GONG is the real issue.
Assuming that your EGT gauge is fairly accurate, If EGT's are measurably LOWER than what I posted above for an ISX in max-load conditions ... I.E.> your making 500+HP and climbing a hill at 100% throttle.. and you have decent boost.. and the EGT's are only 800-F or maybe 900-F post turbo, ... This could be a VERY BAD SIGN!.
THIS IS A HIGH INDICATOR that your engine is absorbing a lot of this heat internally, and the combustion heat is NOT coming out of the exhaust system like it should.
The engine is going to make the heat when making the power. What matters is where it ends up!. This is why low EGT's can be a very bad thing. It is NOT some garbage bullarky idea of "the cylinders are running cooler" bulls#$it.. but a REAL PROBLEM!. Cooler than normal exhaust for high power output is a real issue, and most of the time, is a sign of the engine being harmed/tortured internally.
Lower than normal EGT's is also often coupled with oil temps being able to climb faster, or are always running higher than normal. This is a secondary sign that the a lot of heat from combustion is being absorbed internally and not coming out of the exhaust like it should. - Its a very bad place to be, and is a common sign of bad delete programming where some yahoo has jacked with things like injection timing or other settings in harmful ways.
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== == HIGH EGT"s vs. the numbers and conditions that I posted above. Proper exhaust temps output from the engine is a good sign that the heat from combustion is NOT being absorbed. High EGT's are not a sign that "the cylinders are running too hot" .. thisis a kinf of kind of bullarky statement from people who know nothing about engines.
Excessive EGT's (+1200-F and above) is an indication that the engine is not absorbing as much heat as it normally would before it comes out of the exhaust. - This is usually only coupled with boost levels being lower than normal vs the numbers mentioned above. Holset stated to me once a long time ago that their turbos can handle (post turbo), 1250F sustained EGT's'.. and handle 1350F for up to 3 minutes ... but someone needs to look this up if they want more accurate info.
RE: CM870 tuning - Magnat1976 - 06-27-2026
Thanks Rawze, for great response,ill be doing delete programming with Running rough today.
I am driving this truck for couple months, but not happy.
Drove with with everything plugged in ,it running with surging boost,but reaching up to 36 psi,and I dont feel 500 hp and poor on fuel
I tried as you mentioned, unplugged 2 connectors from egr valve and egr temperature sensor, that boost surging seems disappearing, but it derates the boost,up maybe to 25psi,and runs lazy..and engine light is on.but better on fuel.
Yesterday I tried the trick, I hooked the an extra egr valve to the harness to cheat,it drives,but I am getting delta p sensor -value too high error..is it clogging?
All sensors-delta p,back pressure,boost pressure and temperature sensors are new,egr valve,cooler factory red..its old truck but 660k miles
About Egt I put pro on exhaust manifold, not inside..and dont have hills
RE: CM870 tuning - Rawze - 06-28-2026
(06-27-2026 )Magnat1976 Wrote: ...
Yesterday I tried the trick, I hooked the an extra egr valve to the harness to cheat,it drives,but I am getting delta p sensor -value too high error..is it clogging?...
About Egt I put pro on exhaust manifold, not inside..and dont have hills
There is no need to "trick" it ... that is a bunch of horse-malarly. The CM870 ecm programming already has an EGR-off mode built into the factory programming. - All anyone has to do to put a CM870 into its proper no-egr operating mode (assuming this is for troubleshooting purposes... ehemm), is to unplug the EGR temperature sensor (and leave everything else plugged in properly),.. located in the egr piping somewhere near the fuel filter area. The ecm will shut off the egr system and close the valve for you if you simply do that. The CEL will be on for the unplugged sensor, but it hurts nothing whatsoever. I have seen people run them that way for a million+ miles, engine is not going to shut down over this. - It will have a boost derate, but not a power derate when in this condition. Boost will spike to about 36, then fall off to about 32 psi and hold there. POWER will NOT be lost due to this. - This is normal when egr is off on factory programming and no one has adjusted ecm it to stop the slight boost derate.
RE: CM870 tuning - pwhittle - 06-28-2026
Is there programming that can remove the CEL?
RE: CM870 tuning - Rawze - 06-29-2026
(06-28-2026 )pwhittle Wrote: Is there programming that can remove the CEL?
forum member 'running rough' does this for the older CM870's.