intermittent miss on 3 different trucks

[lcmartin]

Ok here goes, i have my truck (in the sig) that has a noticable miss when the air temperature is below 40 deg or so. The colder it gets, the worse it is. But it only happens when the engine is under a slight load, not at idle, not at wot. The higher the chip is turned up the more noticable it is also. When the outside temp get above 50 or so I can turn the chip up as far as I want and I'll never feel it.Now my dad's truck is an '02, 6 spd, has a 70 hp bully dog chip on it also does the same thing. Not as noticable but its definitely there when it gets cold or when you throw a trailer behind it. My dad's spent a lot of time at different shops trying to figure this out. My neighbor's '01, 6 spd, edge ez, same miss. No codes on any of them.After doing a lot of reading and research a lot of ppl suggested a high pressure leak inside the head whether due to bad o-rings, crushed injector tubes, or maybe even bad injectors. Today I put new rv275 injectors in my dads truck with new tubes and o-rings as well. Felt pretty good when i test drove it this afternoon even with the trailer behind it. But i was skeptical and sure enough another terst drive this evening with a slightly colder temp confirmed it was still there. So its back to the drawing board, I'd like to get this fixed or else there's no reason to sink any more money into my truck looking for performance if its gonna keep missing. Just read on another forum to test the alternator, it might be sending a voltage spike. Luckily I'm a diesel tech in training so I have a test bench to use but I'm open to any suggestions. I figured if our 3 trucks have the same problem somebody else out there has to as well and know how to fix it. Thanks in advance for any help

[Mopar1973Man]

Well I would double check all electrical connection like battery cables and such... I would pull the alternator and have it bench tested just to put your mind at ease. Make sure the do a diode test too.As for the miss I would look at fuel pressure and error codes first thing... As for the fuel pressure what is the fuel pressure at idle and what is during road load (trailer) with your foot in the throttle?

[lcmartin]

i've pulled the battery cables and cleaned them up before. fp is 16 on idle, drops to 12 with a load and foot on the throttle. no codes on either of them. forgot to mention the old man has a fass 100 lift pump on his truck.

[dripley]

Have you tried disconnecting the edge/bully dog and see if the miss is still there?

[Mopar1973Man]

Ok... I'm going to push now... what is your IAT temp like during the cold periods? You going to need a live data tool like ScanGauge II or simular to answer this question.If you want to gamble a bit you could try fooling ECM with a 2.2K ohm resistor in the IAT plug and see if it resolves the issue. What this will do is fix the IAT temp to 143*F. This will rule out if the IAT sensor is goofy.But the live data tool would be handy because then you could look at all sensors...

[lcmartin]

Have you tried disconnecting the edge/bully dog and see if the miss is still there?

yeah its still there just not nearly as noticable

Ok... I'm going to push now... what is your IAT temp like during the cold periods? You going to need a live data tool like ScanGauge II or simular to answer this question. If you want to gamble a bit you could try fooling ECM with a 2.2K ohm resistor in the IAT plug and see if it resolves the issue. What this will do is fix the IAT temp to 143*F. This will rule out if the IAT sensor is goofy. But the live data tool would be handy because then you could look at all sensors...

i'll have to check the next time i drive it, the attitude should pick that up i believe right?

[Mopar1973Man]

i'll have to check the next time i drive it, the attitude should pick that up i believe right?

Yes... Juice should do it... I would compare both engine coolant temp and intake air temp they should be exactly the same at cold start if not one of them has failed. Yes its possible for a sensor to fail within specs and not trip error code or light. Hence why I get away with a 2.2K ohm jammed in my IAT plug...

[lcmartin]

checked this afternoon and the iat and coolant temp matched up with ambient temp on startup. thanks for your writeups btw moparman. i did the injectors start to finish with your article.

[Mopar1973Man]

Ok so how about the miss problem?

thanks for your writeups btw moparman.

Thanks for the comments...

[lcmartin]

the miss is definitely still there. i have a trailer i'm towing tomorrow, i think i'm going to unplug the chip again and see what happens. if i remember right last time i did you could still feel it sputter just a little bit. nowhere near as noticable with the chip on though. also just had a thought, could this be a fuel temperature problem? neither me or dad has a fuel heater since we both have aftermarket lift pumps with the half in line going into the injection pump. but if it was that shouldn't it fix itself after a while of returning warm fuel to the tank?

[Mopar1973Man]

Like myself I've got a stock fuel heater with my AirDog 150 as well hooked up and even then it takes several miles like 50-60 miles to warm up that full tank of fuel from near 0*F temps. You got to remember the fuel leaving the engine and VP44 might be warm but by the time it flows back to the fuel tank through the steel return line it will be much cooler.But fuel temperature problem would be visable on the fuel pressure gauge with a serious drop lower than typical like me I lose about 3 PSI from typical with temps as low as 0*F. I don't use any fuel anti-gel either.I'm thinking its a fuel system related problem for sure but what I'm not exactly sure yet...

[2500ctd]

Is that resistor green, blue orange? 56Kshould be red, red, red iirc.

[Mopar1973Man]

56K ohm is for 3 cylinder high idle.

39K ohm is for 6 cylinder high idle.

[lcmartin]

well i pulled the alternator but couldnt make it work on the test bench so i put it back on and left it disconnected. ran the truck a few miles and still got the same miss.

[lcmartin]

New question. I was cruising cummins quickserve online to resolve this problem, after checking multiple fuel related issues, most of which i should have ruled out already, it said to recalibrate the ecm. What does that mean, reflash it or get a new ecm? I do wanna check the turbo first just bc I havent seen it in awhile. Also is there a chance the electronic governor is too aggressive and is there any way to change that? Bc it seems like it happens mostly when i let off the clutch and lug it just slightly but it will still miss with my foot in it on its way up the powerband. Also I can see my APPS percentage drops a few points when it misses, I reset it with no results. I should do some more testing with that too to see if its the sensor or the ecm. Anyway theres several questions in there, what do you guys think?

[mr.mindless]

A miss/ hesitation under heavy load sounds just like what my buddy's '01 went through. We fought and fought with it, ended up taking it to a dealership, and it got two ECUs put in it after replacing the APPS three times didn't fix it. It got 99% better with the second ECU but he says he still feels it every once in great a while which has him wishing the VP44 would crap out and have good reason to replace the last likely culprit and know​ it's fixed.

[lcmartin]

so heres the latest on this thread. i pulled the iat sensor and drove it around a little bit. the miss is still there but not nearly as often and not as noticeable when it does happen. with the sensor unplugged the intake air reads 114 deg. then i tried the same thing with my old mans and it made no difference to his. now my question is if the ecm reads a colder temp does it advance the timing too far in my case? then someone told me the vp44 pump is keyed and if you get a new key you can advance or retard the pump up to a degree or two without having to mess with the ecm and not messing stuff up. has anyone heard of this? what does it entail? and is it worth it or is there an easier way to retard the timing besides putting a resistor in the iat?

[bristoy]

have you checked your map sensor.i had simular sounding symptoms with my 01.it didn't show any codes tripped but i replaced it and the issue cleared up.hope this helps.

[Timbo]

I would fool the iat circuit, I have fixed a few trucks with that very problem with a 1K resistor in the iat circuit. I actually had that problem with my truck and beat my head against the wall trying everything and that fixed it. Some trucks with big injectors and timing boxes it happens. With my edge on, below 55 deg out it would do it. It would also be a good idea to put in a 190 thermostat. Timing seems to be the issue because my smarty with no timing. there was no miss. The ecm thinking its hotter pulls timing out. Its worth a try, about $2 at radioshack.

[lcmartin]

just tried what you said timbo and it took out the miss completely. Now just to wire a switch in the dash so the grid heaters are functional when i need them to be and im set. Then i just gotta fix the old mans problems. He might have a different issue bc when i unplug his iat sensor there's no difference to his miss. Unless the 02s ecm is programmed slightly different. He doesnt have guages so its a little harder to tell what his ecm is reading.