My '95 K1500 is a MAP system with no AIT sensor. Are there F-bodies with this same set up? Does any one know how to tune this system? I've already changed my injector constant to solve a lean condition and bumped up the timing table a couple of degrees across the table, but I'm stuck here. I need to get this thing tuned so I can get it inspected(went out in June!!).

Thanks for any help

Tedd

 

Fbodys have the IAT.

Trucks rely on the thermac control in the air cleaner to keep the intake air at a *relative* steady temp. Thus *eliminating* the need for IAT compensation in the ECM. I'm guessing it was a fudge because of the lesser emmission standards applied to trucks........

Stuck where?

Tuning is measuring engine performance.

At part throttle you tune for INT and BLM close to or slightly less than 128.

Timing at part throttle is tuned looking for the least amount of timing required to run the least amount of TPS for load X.

In other words: You want the least amount of TPS required to go 70mph on a given stretch of road. Too much timing and you'll need more throttle OR the engine will detonate and you'll get knock counts.

 

Thanks for the response! There is no sensor on my aircleaner or in the intake fresh air duct work. Even on DataMaster for $OD there is a IAT data cell, but it is not used. A IAT is also a thermac sensor isn't it? I have even found the plug in the wiring harness for an IAT sensor, but it is unused on my '95 Suburban. It seems like I read somewhere that this system gets around using an IAT by comparing the MAP reading with outside barometric pressure. Am I even close on this one?

the motor in the truck was purchased as a Summit Racing tow motor, a 350 bottom end with a Crane RV cam and Trick Flow heads. I originally had the motor in an '87 3/4 ton and with the help of a Jet Aftermarket Chip it ran like a big block, I mean the power really was outstanding! Well I put the same motor in my '95 Suburban and it's never had the same power much less smoothness that was present in the '87. Are the bin files at all similar between the '87 and the '95? I other words can I use the VE tables and Timing tables from the '87 Jet chip in a '95 PCM?. The '95 defiition file is a $OD and when I read the Jet file Tunercat told me I needed $FF def file. I have got my blm's very close (by changing the injector constant) but every time I change my timing tables the blm's change slightley. While I have'nt done a timing analysis at different TPS or MAP readings, it seems there should be other things to pursue after those are close if not right on, such as PE settings and such.

Another question I have is the differrence between tuning of a 1/4 mile car vs. a tow rig or truck. The settings for a lightweight high horsepower car the fuel table and timing tables must have different shapes and characteristics than a heavy (5800 lbs) higher torque rating than horsepower rating motor. Does that make any sense?

any other truck tuners out there?

Tedd

 

IAT is not the Thermac system. Perhaps Thermac is the wrong term. Anyhow, what I was refering to is the heat stove on the exhaust manifold that is connected to the air cleaner. The flap in the air cleaner is thermostatically controlled and draws heated air from around the exhaust manifold.

The ECM does calc barometric pressure on startup and some do it when you go to WOT. I don't know if this relates to not having IAT.

Don't give IAT another thought, its not a worry since your 'burb doesn't use it.

I wouldn't bother trying to insert the 87 tables onto the 95 tables. Trouble is, you don't know what else JET did in the chip to other timing tables that may or may not be listed in Tunercat. Testing and analysis will get you max performance. There really isn't any quick way to get there otherwise.

Tuning any truck or car is the same. You read what the engine wants and make the appropriate change. The fuel and spark curves will have different shapes than a HP car engine.

 

Thanks Brent, I appreciate your input. I have gotten quite a bit of improvement from my new settings vs. the OEM settings, it just seems to be not quite there yet. I'll keep after my fuel and timing tables and see if that offers any improvement. As I modify my VE tables to run 128 blm's, is it normal (I expect it is) for the VE tables to need to be readjusted after some timing changes are made? In other words, after I get one table correct and move on to the other. So I'll have to go back and forth untill the change is so small that it's not noticable?

Looks like I'm in for some more data runs today


Tedd

 

Yes, it is normal for changes to the timing table to affect the INT/ BLM. You'll probably have to go back to the fuel table a couple times to clean it up. Not nesessarily everytime you change the timing tables.