Engine/Transmission (1998.5 - 2002) IAT sensor readings - how hot does it get, how does it affect timing?

[GOT-Torque]

I know there are many variables to affect this, but what would the range be? Does it start to defuel at a certain temp?



Also, if anyone knows how this reading affects engine timing, please chime in.



Thanks for any input.

 

[johncameron]

I'd like to follow this one!

 

[ERuhl]

There's some IAT info here including the expected resistance values:

DodgeRam.org

 

[GOT-Torque]

I'm trying to solve an issue that I have when I turn my edge box on when it is cooler than 50 degrees out. I believe it is adding too much timing as any time I try to accelerate, it is a violent miss/shake/hesitation until I get out of the throttle.



I just pulled my IAT out, cleaned it, and checked the values at varies temps. It seems ok, very close to the specs it should be. So I reinstalled it, and added some jumpers to the IAT wires and ran them into the cab. I will be adding a switch with a resistor in parallel to the IAT resistance that will effectively cause the ECM to see a lower resistance (which equates to a higher intake temperature) and pull timing back out. This is an attempt to verify it is a timing related problem.



I'll report back my findings...



I'm also adding a seperate switch with a different value resistor in an attempt to start the 3 cyl mode when currently in high idle (without needing insanely cold temps).

 

[timbo]

You will need around 1k I just solved this exact problem! I have a radio shack 50k linear taper potentiometer. I turn it to about 40k when its real cold so the grid heater works properly, then turn it to 1k(thats what i needed) i also have a 200 ohm resis inline so the value can never go to 0 ohms. I KNOW THE VIOLENT/ MISS/ SHAKE THING VERY WELL It could not run any better NOW! Also just installed a HTT 62/12 and TAPPED, as my reward! Oo.

 

[johncameron]

I'm also adding a seperate switch with a different value resistor in an attempt to start the 3 cyl mode when currently in high idle (without needing insanely cold temps).

If this works... ..... please tell us Emagine a 3cyl idle in the summer :-laf :-laf

 

[GOT-Torque]

I'm planning on using a 1k in parallel with the sensor to drop the overall resistance to just less than 1k (assuming regular sensor reading is around 10k while driving right now).



On another note, the 3 cyl idle mode would only work when coolant temp is still below 140 (unless you alter that signal as well). I was just hoping to enable the 3 cyl mode when just below 32 degrees.

 

[timbo]

I'm pretty sure it will not go in 3 cyl unless the CTS is also fooled but i'm pretty sure it can be done!

 

[ERuhl]

I'm trying to solve an issue that I have when I turn my edge box on when it is cooler than 50 degrees out. I believe it is adding too much timing as any time I try to accelerate, it is a violent miss/shake/hesitation until I get out of the throttle.

I had the exact same issue, you can search my previous posts to read about it. Timbo also had the same issue, but he was able to fix it by bypassing the IAT sensor. I followed his suggestion and tonight I unplugged the IAT sensor and bypassed it with a 1k ohm resistor. Fired it up and went for a drive, NO MISS!! Timbo is da man Oo. Oo.



I'll run the resistor for now, but I picked up a potentiometer as well for future in-cab adjustability. I also just started looking into substituting coolant temperature for air temperature. I'd like it to be automated so the intake heater grid will work when the engine is cold and the extra timing will be pulled out when it's warmed up, but if I have to flip a switch so be it. For now it's just soooo nice not to have the miss anymore :-laf



Does anyone know how to change the base timing?? Ideally I'd prefer not to have to fool the ECU and just fix the root problem.

 

[GOT-Torque]

I really wonder why some of us have this problem and others don't? It's like some trucks started with more base timing than others???



Along the same lines, is the compression ratio of a diesel engine directly related to timing? In other words, the higher the compression, the sooner the ignition of the fuel will start? Is this why most big HP trucks run lower compression? They can add way more fuel and air than a stock motor and run at higher revs without the problem of too much timing or too early of ignition. I guess my question is could I either run a larger headgasket to lower my compression ratio or pull timing out (for example fooling the IAT sensor readings)? Same overall effect? or am I off base here?



Timbo, what is the CTS? Thanks!

 

[ERuhl]

I really wonder why some of us have this problem and others don't? It's like some trucks started with more base timing than others???

That's my guess as well.

what is the CTS?

Coolant Temperature Sensor.

 

[timbo]

In a diesel engine ignition occurs at the exact time the injector starts to spray. Years ago, i was taught lowering the comp ratio enables you to increase BOOST levels without EGTand cyl pressure getting out off control. Naturally the more air that is forced in directly increases Comp ratio. The one thing we seem to all have in common is bigger injectors! Heres my theory! The ECM starts to inject a very small volume of fuel before TDC the rest AFTER TDC thus starting IGNITION. For an example,lets say the INJECTION squirt starts@ 6deg BEFORE TDC and continues to spray til 20deg AFTER TDC. with stock inj. the volume of fuel injected BEFORE TDC is not enough to make an adverse reaction on the piston. But with larger injectors(and the EDGE) the volume of fuel injected BEFORE TDC is greater. I think its enough of a bang in the cylinder to want to drive the piston back down,before it gets to TDC! Like a high compression gasser on 87 octane,(preignition) Good thing this engine is so durable,cause this has got to be HARD on it! On the other hand most guys do not have this problem. i think the cam sensor location,or machining of the crank gear,cam gear or the teeth on the back of the cam gear is, OFF a little bit. There is definitely a reason why we have to much static timing. This is just my opionion, and the actual # of degrees in the example is just a guess. I wish i Knew exact duration of the squirt and how many deg before TDC and after TDC it occurs. What we have all been desribing is NOT a miss at all. Its to much of a bang in the cyl to EARLY! Does anybody know a procedure to mechanically check base timing?

 

[RCenters]

One thing I have heard of is swaping the keys around on yr pump , sence some r advanced and some not . .



I know a guy who is working on a timing only control so a person could advance or retard timing , it goes in between the cam sensor and ECM

 

[ddunk]

Thanks Guys, very Interesting

 

[ERuhl]

I know a guy who is working on a timing only control so a person could advance or retard timing , it goes in between the cam sensor and ECM

Excellent, an adjustable cam sensor or something that alters the signal is exactly what we need.

 

[GOT-Torque]

Got the switch installed. First of all, holy crap :--)



Bottom line, I was able to run my comp drag box for the first time since last summer and I've installed the twins and a smarty since then On 5x4 with the smarty on SW6, boost was somewhere between 50 and 60 and I was really movin' No problems with too much timing anymore! Smooth acceleration Oo.

 

[AHire]

Where do i get a switch? If i got a 1k rsister do i just plug it in the pigtail instead of the sensor?



Pix please Oo.

 

[GOT-Torque]

Just use a cheap switch from radio shack. I used T-taps on the IAT wires. Tapped into one wire, ran to the cab, thru the 1k resistor to one side of the switch. From the other side of the switch back out of the cab to the other IAT wire. When the switch is open, it has no effect on the IAT sensor resistance, when the switch is closed it puts the 1K resistor in parallel with the IAT sensor resistance. For example, if the IAT sensor is around 10K and you close the switch, you would end up with just under 1K of total resistance (which fools the ECM into thinking the IAT temperature is close to 200 degrees.

 

[SKargo]

I'm doing some interesting beta testing with a module and part of it is fooling the IAT, WOW!

 

[NoSeeUm]

.....

The ECM starts to inject a very small volume of fuel before TDC the rest AFTER TDC thus starting IGNITION. For an example,lets say the INJECTION squirt starts@ 6deg BEFORE TDC and continues to spray til 20deg AFTER TDC. with stock inj. the volume of fuel injected BEFORE TDC is not enough to make an adverse reaction on the piston. But with larger injectors(and the EDGE) the volume of fuel injected BEFORE TDC is greater.

... .

Good post Timbo. That is the nice thing about the 3rd Gen CR and the adjustability of the injection event(s). On 24v 2nd Gen the injector simply pops open once sufficient pressure is produced by the IP.



As you said the idea with timing has allot do with the moment arm geometry of the piston rod / crankshaft position. The idea is so that the greatest amount of force is exerted on top of the piston with the crank at the optimum rotational position.



Of course the force needs to be exerted after the piston goes past TDC. But too soon and the rod is standing on top of the crank. Too late and the force is not released efficiently due to much more piston movement. This greater movement allow more expansion of the combustion gases vice the gases just exerting maximum downward force and not expanding much. The number I was told was that the fires go out around 16 degress (+/-) PTDC and that is where peak cylinder pressure is attained.



The burning of fuel takes a fixed amount of time. The faster the engine is rotating the sooner the fuel must be injected for it to complete the burn at the proper crank position. So advancing the timing is a necessity.



OK, enough over information.



It seems 50F is some sort of a magic number with IAT and how the ECM SW changes on the timing curve. With my dying VP44 I would get a romp-romp-romp wierd idle pretty much below 50F. I have also noticed that my engine has a noticeable increase in timing ping below that temperature.



I am guessing the purpose for the point on the curve is for emissions control above 50F. Where below 50F it must be not as much of an issue. Above 50F timing must be retarded to reduce the combustion temperature and the formation of NOx.



Jim