Engine/Transmission (1998.5 - 2002) Miss only with edge on, FIXED!

[NoSeeUm]

Just stuck it in for now. I am waiting on a wiring extender harness. The engine sounds very nice with a 5. 6k (100F). There are cab noises I don't remember hearing before.



I was thinking to remove the IAT sensor altogether and just use 35k and a switchable 6. 5k in parallel, as ERuhl suggests. To fool to 40F or 100F. That way my grid heaters will work for cold starts. It might actually be easier to just hard wire the grid heaters with a switch vice the IAT. But then KISS starts to go bye bye and my truck gets harder to drive by anyone but me. Have not decided on my full plan yet.



I found out that with the IAT disconnected the ECM reads -40F and throws a 0113 code. No big surprize there.



Gary, what is your purpose for the 1200 - 500 ohm thermister?



Jim

 

[Gary - K7GLD]

Gary, what is your purpose for the 1200 - 500 ohm thermister?

At the time I ordered it, I was hoping for a far greater resistance swing with changing temperature - I'm not at all familiar with thermistors, so the various equations and formulas furnished by Mouser for determining their characteristics is pretty much Greek to me - so had to just make a "best guess" with what I could decipher from the descriptions.



As it turns out, the cold temp resistance is pretty much on-target, but the swing could undoubtedly be greater, and probably should swing the opposite direction for better implementation - a "Negative Temperature Coefficient" instead of the positive I have, not sure yet.



As it is, the Thermistor resistance by itself, with the added series 1 Meg pot at it's lowest resistance setting, will be pretty much the same as the 1K fixed setup others are using - and will to a limited degree, follow engine temp rise in it's swing - to a point - but I don't know what that point is, or how much more effective it is than a simple fixed resistor - if any.



Then, once the engine starts warming up, the 1 Meg pot can be adjusted for best engine operation as desired - and again, without trial and error, not sure if that adjustment capability is of value, or even needed - only time and test will tell.



It would probably be enough to get a cold engine started, to simply turn the pot to it's maximum 1 Meg position, then once the engine starts, down to it's lowest point for the Thermistor to take effect, But I will get one that includes an off/on switch so the whole added setup can be switched in/out of the circuit at will, and at least all that added setup will only require a single control knob for operation.



Obviously, the Thermistor alone could provide the lower 1K resistance itself - but I figured it would be easier to provide an external series resistance (Thermistor in this case) of a value already known to be adequate for the purpose, than have to precisely set a large resistance variable - seems more complicated in description, but really pretty simple and easy in use.



The Audio Taper ! Meg pot I plan to use will allow a greater spread of resistance at what I will use at the end nearest the external Thermistor, allowing easier and more gradual resistance change at that end of travel - dunno how critical that adjustment will be, or how effective - again. only testing will tell - the pair of switched fixed resistors you mention may well do all that's needed.



But, at this early point, I still feel that if base timing that is off so far as to need "fooling" for COLD temperature operation, surely, it could ALSO use some fine tuning after the engine warms up for added help - that's my purpose with the 1 Meg pot...



Wish me luck! :-laf:-laf

 

[Gary - K7GLD]

OPPS! - almost forgot to ask about this one:

Just stuck it in for now. I am waiting on a wiring extender harness. The engine sounds very nice with a 5. 6k (100F). There are cab noises I don't remember hearing before.

Are you saying you are using a single 5. 6K fixed resistor that is working to correct your cold temp running - but still permits what appears to be proper engine operation AFTER the engine warms up?



I this morning have ordered a 1 Meg audio taper pot, and also a pair of small disc thermostats - both with normally closed contacts - one opens at 80-90 degrees, the other at about 165. The thought here is that they might be useful in a fully automatic setup that will automatically remove any added resistance once the engine hits a predetermined temperature...

 

[DCreed]

WOW ! that link to clean the IAT was a 5 min job and worked great! thanks guys!

 

[NoSeeUm]

OPPS! - almost forgot to ask about this one:



Are you saying you are using a single 5. 6K fixed resistor that is working to correct your cold temp running - but still permits what appears to be proper engine operation AFTER the engine warms up?



I this morning have ordered a 1 Meg audio taper pot, and also a pair of small disc thermostats - both with normally closed contacts - one opens at 80-90 degrees, the other at about 165. The thought here is that they might be useful in a fully automatic setup that will automatically remove any added resistance once the engine hits a predetermined temperature...

Yeah... .



From watching my IAT I have noticed that at about 80-100F the engine really quiets down. Keep in mind, timing stutter is not an issue for me.



But so far, all I have done is disconnect the harness from the IAT sensor and stuck a 5. 6k resistor into the slots of the connector. I doubt it will start or start easily in cold weather, because my grid heaters will not come on. I must park the truck inside (heated) or plug in my block heater for a cold morning start until I complete this project.



So basically, cold engine or warm engine it runs fine. No issues yet, other than start problem as I mentioned above. In fact, so far I am really pleased about how quiet it runs.



Not enough time to check on mileage yet. My plan is to run a XZT+ in timing mode when I want to stretch out the MPG. Currently I am getting 16-17 around town.



Jim

 

[Gary - K7GLD]

I sorta suspect that the function of the IAT, and specific resistance vs temperature may well NOT be as critical as we suspect. Sure, undoubtedly needs to be REASONABLY close to a standard reference, but percentage wise, probably can vary a significant amount from one truck/IAT to another, and still deliver what appears reasonable all-round performance.



When all my ordered components arrive and are installed, it will be interesting to see how critical various settings of the potentiometer are, and their observable effect on engine operation in varying driving conditions.



It will also be interesting to see effects on adjusting - fine tuning - for best power, as well as for best economy. My overhead instant MPG readout should be helpful in that category - no, not precisely accurate, but usable for comparative readouts as resistance setting changes are made.



I remember some years back, there were devices sold that attached to the distributors of gas engines that had an adjustment knob that the driver could use to fine-tune ignition timing as the vehicle was in motion - not sure how effective those were, but this experiment on the diesels might function much the same way...

 

[paulb]

IMO the more highly modified the pickup, the more gains you will see by moding the IAT. Larger injectors, higher (cooler) boost, larger intercoolers, all cause the timing values to be farther off. This time of year, I can get my truck to do the timing surge on demand, so it won't be hard to see gains.



Paul

 

[Gary - K7GLD]

OK - not a lot of cold weather so far in most areas of the country - but don't want this to die out...



Here's what I've accomplished so far:



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The above is the IAT extender cable mentioned earlier in this thread - my IAT itself was very clean, and required no attention at all - a test of temperature vs resistance showed it to be right on the money according to available charts. The "lumps" visible in the harness are radio frequency filters, toroids, to filter out interference from my mobile Ham Radio setup - 20 meters was always a big problem, and another Ham TDR member told me a filter in the IAT lead had helped him, so I added one to my main harness, and another to the lead that goes into the cab of the truck.



I'm using the 1 Megohm potentiometer shown, with a 1K fixed resistor wired in at one end of rotation - that allows easy adjustment to the base resistance while in motion, then the pot can be adjusted as desired for fine tuning. The potentiometer also has an on/off switch that allows the whole added resistance package to be completely removed from the IAT circuit at will.



Here's the IAT control arrangement as installed in my ashtray:



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The small switch seen on the lower edge of the panel is the manual on/off switch for the blower I use to flow cooling air over my VP-44 injection pump.



Results so far are pretty worthless - temps are around the mid 60's, and there seems NO observable effect with the added resistance in or out of the circuit, or anywhere in between - the truck starts normally at all settings as well, so will have to wait for colder weather for conclusive testing - as I suggested earlier, it may well be that the function of the IAT is far broader and less critical than I thought, at least as far as any "fine-tuning" is concerned. If so, it might be simpler to delete the potentiometer completely, then use one or both of the pair of small button thermostats I also bought, then just automatically switch a couple of appropriate fixed resistance values in/out of the IAT circuit for selected temperatures as they occur.



This is still very much an experiment in progress - and no answers yet as far as adjusting IAT reistances are concerned - but the added RF filtering toroids DID wipe out the 20 meter Ham Radio interference I previously had, so all this was worth the effort, even if there isn't any IAT benefit so far...

 

[Gary - K7GLD]

Here's something that might be useful for other guys working on the IAT sensor - maybe not too many affected yet this season, but when colder temps hit in ernest, this thread WILL heat up! :-laf



When I swapped out my VP-44 a while back. I removed and left off the rear engine hoist gadget that is mounted to the intake manifold - made it lots easier to get at and work around those rear injectors. I found out a few days ago when working on another project, that the fearsome task of getting to the IAT for servicing was also lots easier - only a couple of minutes to remove the plug and harness, then a 13/16 sparkplug socket to remove the IAT itself - piece of cake!



Here's a shot showing how visible the IAT is once that engine lift device is out of the way:



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You can also see the short bolts I had threaded back into the manifold where the lifting attachment had been installed...

 

[NoSeeUm]

Can anyone recommend a good 12 volt holding relay with at least one NC and two NO auxilliary contacts?



I am thinking of doing a "live man" switchable set-up so that my grid heaters will always work by default. I realize this complicates the installation, but I have decided to go this way mostly to simplify things should my wife need to drive the truck.



She already gets freaked out by just climbing up into the drivers seat.



Jim

 

[Gary - K7GLD]

What current rating?



Mouser Electronics - Electronic Component Distributor



Has all kinds...

 

[Gary - K7GLD]

On a related "grid heaters" note - after the above described mod to my own IAT, and an early morning engine startup temperature of about 50 degrees and the added 1K resistor in the circuit, my grid heaters are still cycling just as they always have - no change!



Dunno if that will hold true as temps fall lower - but in the case of my '02, it appears that there are other conditions related to ECM programming and sensors that also contribute to and control the heaters than just the IAT...

 

[ERuhl]

On a related "grid heaters" note - after the above described mod to my own IAT, and an early morning engine startup temperature of about 50 degrees and the added 1K resistor in the circuit, my grid heaters are still cycling just as they always have - no change!



Dunno if that will hold true as temps fall lower - but in the case of my '02, it appears that there are other conditions related to ECM programming and sensors that also contribute to and control the heaters than just the IAT...

50 degrees is warm, the described issue is with cold starts. Think snow.

 

[Gary - K7GLD]

50 degrees is warm, the described issue is with cold starts. Think snow.

You missed my point?



IF the grid heaters are still operating at 50 degrees with the 1K resistor added, they DERN sure are also gonna work down at 30 degrees - resistor or not!



As I recall, the cutoff for the heaters to NOT work as setup in OEM, is 55 degrees. I would think that with the ECM *thinking* the IAT temp is up around 150 degrees with that added 1K, the grid heaters would not be operating...

130° - 4K ohms

167 - 600 to 675 ohms

212 - 600 to 675 ohms

The above temp vs resistance chart range is pretty close to what my 1K resistance mod produces in parallel with the IAT at 50 degrees ambient...



Wasn't it you who commented that the heaters would NOT work with the resistor added:

What heater grid? The ECM thinks it's 80°F, you don't get the heater grid. I tried cycling the grid repeatedly, and it's just not on long enough to make a difference. Now if the ECM thinks it's 32°F, like it actually is, then you get the nice long heater grid cycle.

As I stated - mine are still working and cycling just as they always have - and yes, I have double checked that the resistor IS in the circuit and functioning properly...



I'm wondering if perhaps the coolent temp sensor is a factor here, as well as the IAT...

 

[WTBurke]

I'm following along here as noted before. With Gary modifying this single input and finding the grids still cycle this leads me to the same conclusion that there is more that the ECM takes into consideration for cold temperature operation.



The only reason I'm chiming in here is to be honest with my hidden agenda and I'm certain I'm not alone with these thoughts. I am trying to find a way to electronically fool certain sensor parameters to cause high idle to ramp up earlier than what is set in programing within the ECM. ALSO... once these are found perhaps we could take it to the next step and have 3 cylinder idle too, at say 25 degrees F.



There are many reasons that several of us would care to have some of these features operational outside the normal parameters.



For those of you who have posted photos of the stick on the accelerator peddle please don't bother helping me with hay-seed antics. Also, doing the little trick with the APPS is not what I'm referring to as this upsets the ECM in it's purest form too.



So... anyway... I'm telling my little secret and perhaps I'm not alone along this train of thought.



I know this thread is about timing and miss under certain conditions but, it opens other lines of thought... .



So... be honest... who else is thinking what I'm thinking?



William

 

[Gary - K7GLD]

The only reason I'm chiming in here is to be honest with my hidden agenda and I'm certain I'm not alone with these thoughts. I am trying to find a way to electronically fool certain sensor parameters to cause high idle to ramp up earlier than what is set in programing within the ECM. ALSO... once these are found perhaps we could take it to the next step and have 3 cylinder idle too, at say 25 degrees F.

IF fooling the ECM by only juggling added IAT resistance to make the ECM think is WARMER than it is will work (and it apparently DOES NOT fool the ECM into shutting down grid heaters!), then adding more resistance in SERIES with the IAT *should* also make the ECM think it's COLDER than it really is, and kick in the features you are looking for...



(EDIT)



In your case, a simple 10K or so pot in SERIES with the IAT would probably do the job - and all you'd need do is crank in full resistance at startup to engage the fast idle and such, then once the engine is warm enough to suit you, crank all the resistance OUT, and normal IAT/ECM operation should be restored...

 

[paulb]

With a 1K ohm resister in series (ECM thinks it's about 100*), my grid heaters will still cycle once started, if it's cold enough. However, the grid heaters will not come on, until it is started. It seems that the ECM uses the IAT to turn on the grid heaters, before startup, and then other parameters once it has started.



Paul

 

[Gary - K7GLD]

With a 1K ohm resister in series (ECM thinks it's about 100*), my grid heaters will still cycle once started, if it's cold enough. However, the grid heaters will not come on, until it is started. It seems that the ECM uses the IAT to turn on the grid heaters, before startup, and then other parameters once it has started.



Paul

You DID mean in PARALLEL didn't you?

 

[paulb]

You DID mean in PARALLEL didn't you?

Nope. Unplugged the IAT and connect a 1K resistor in series (resistor across the two terminal of the wiring harness).

 

[Gary - K7GLD]

AH - gotcha - I forgot your "KISS" setup! :-laf