grabbem88

Hey guys.... Been a while

Here is my issue when I have the IAT plugged in..

When you take off car bucks breaks (lean) wont accelerate

Unplugged car runs for the most part decent..

No codes replaced 4 times no breaks in wires that I saw..

I think all this started last winter and never got back to this site to ask why when plugged in it drives bad unplugged good

Thanks art

grabbem88

I just noticed my info isn't showing anymore..

1993 z28 m6 246k miles on it!

Hooker LT's y and flow master and cai

Injuneer

Did you post from a phone app? Some of them do not post the "signature".

At any point have you tested the sensors (4 replacements?)? Have you verified 5V to theharness connection (harness unplugged)?

4th Gen LT1 F-body Tech Articles

The IAT shares a ground with the MAP sensor and the A/C temp and pressure sensors. Possible there is a problem on one of those circuits that is screwing up the voltage on the IAT sensor, or vis-a-versa.

I would check the IAT sensor resistance, check the voltage at the harness connector with the harness off the sensor, then check the voltage with the harness on the sensor. Record the actual air temp at the same time you check the voltage with the harness on the sensor, and post them. I'll tell you if there is a voltage problem.

Alternatively, use Scan9495 to data log your ECM. It now works for 93's as well:

https://www.camaroz28.com/forums/com...95-lt1-874306/

Then we can review the MAP and IAT side-by-side.

grabbem88

Yeah I was using my phone didn't realize that possibility

No never tested for volts assumed it just crapped out the first time

My a/c stuff is all yanked out so gonna have to double check that

The ground that ties the map and IAT wouldn't by chance be down on the block would it... Not soon after header install this IAT issue started....

Thanks for replying and I also ran codes after hard wot run to see how bad this was affecting the car and ses light came on and then shut off when I let off gas..

Code 55 came up so I got other issues at hand as well unless this IAT/map is creating this??

Fuel filter was replaced with a wix yesterday with oil change. Somehow old filter got clobbered a smashed it...


Again thanks

Injuneer

The ground is actually a black wire that starts at pin B3 of the ECM, not on a chassis or engine ground.

DTC 55 is "fuel lean" and sets when you go heavy on the throttle, the ECM goes into power enrichment (PE) mode, and richens the A/F ratio to make power. If the O2 sensors don't show it's running rich, like it should, DTC 55 sets.

In a 93 with speed-density A/F ratio control, the inlet air temp and the manifold absolute pressure are critical to determine the mass air flow, so that the ECM can add the required fuel. The IAT problem and DTC 55 could be (and likely are) directly related.

grabbem88

Wow thanks been driving me crazy in what I did or didn't do..

I know my car has had several pig tail issues like my vss everything checked until I plugged it in and it shorted put

So I will check all what you said

grabbem88

All I got is a meter and the plug only has less than 3 volts key on

grabbem88

Scratch that lol been a while had it on batt load..

Unplugged 4.89. Plugged 4.00

GaryDoug

4.00 volts corresponds to 63-64 degrees F.

grabbem88

So any clue my car runs like crap when plugged in?? I can't even cross an intersection with it plugged in

Injuneer

Next check the MAP sensor at idle. 5V reference between the black and gray wires, sensor off or connected - doesn't matter. Check with the IAT sensor connected and unconnected. Next the signal wire, measure light green to black, connector on the sensor. Should be about 1.5V. Again, measure with IAT plugged and unplugged.

Injuneer

Looking at some of my old data logs that record both deg-F and voltage, an IAT of 60*F is about 1.5V ?????

grabbem88

Signal wire green with key on is -.002 with IAT plugged and unplugged

Gray to blk test was 5.0v plugged and unplugged with IAT

Unplugg map car shuts off and that should be what happens

grabbem88

Ok engine running the signal wire was reading 1.3-1.7

Everything plugged in right now the car is all over the place

"Hunting". Unplug IAT she idles out unplug she revs for 3 seconds and idles at 750

Plug in she almost died but caught idle tach drops real quick to 500 and back to 700 hasn't balanced out ... This is all cold start warming up. As I'm typing she clears up a little

I think everything is working and this is a fuel pump issue??

Injuneer

For some reason, my response to your post of 3:23pm did not show up - I think we both posted at the same instant.

When did you get the -.002V reading on the MAP sensor? Did you measure green wire to gray wire with engine off? Only way you could get that result. With engine off, MAP voltage should be 4.8-4.9V at sea level, since with the engine off, it's reading barometric pressure.

My last comment, which didn't show up is I think your IAT voltage may be wrong if it's really at 60degF. Factory manual shows same as the date logs I've received, 1.2 - 2.0 Volts. 4.0V is too high. But let Gary look at that.