slow_90firebird

Alright here is the deal.

When I first had the car for a few months, whenever I would unplug the IAT sensor (like running the car with no aircleaner), it would throw a SES light. I believe the code actually came back to an IAT problem, which would be normal.

Now, I can drive all over with out it plugged in, and still no SES light or code. I dont understand what that means. The actual SES light works fine - flashes on key-on, and stays on if anything else is unplugged like a MAP sensor or something. Just doesent come on with the IAT unplugged...

Would this mean a bad IAT sensor, or maybe a wire, or a bad ECM?

Thanks yall

slow_90firebird

Nobody?? Come on guys, the minute I get an intelligent question - no answers.

RBob

iTrader: (1)

Hard to say what the issue is. It can't be that the IAT sensor is bad, as it isn't even plugged in. Is there a resistor in place of the sensor? Was the ECM possibly swapped out for a '7747?

Best bet is to check the connector for the IAT. Then use a scan tool and see what it reports for the IAT value.

RBob.

slow_90firebird

Well, the connector is kinda OK on the IAT. A few days ago, the little retainer clip thing broke off the plug, however it stays plugged in perfectly fine. The weatherpack seal keeps it nice and tight.

Also, I havent had the light come on in over 3 months, however I just remembered that it used to come on when I unplegged the IAT. Like I said, it still does come on for the MAP unplugged, the ESC wire undone, and anything else.

The car has never been modified like that or anything. Factory ECM and factory wiring, and factory sensors.

I almost wonder what the ECM is seeing for a IAT temp. If it is getting a resistance value elsewhere, and it is totally wrong, I wonder if that could have been the cause of the Knock, and not the EGR valve? I mean, the new EGR valve helped some, but I still need to run 93 test, or else I get some knock.

I dont have any way at all to datalog. Not possible for me. Is there any other way I can test it?

S105.7

its a ways off, but im willing to help you datalog at the Colt State Park meet. maybe we can get to the bottom of things with TunerPro RT.-Jim

slow_90firebird

Oh, you have the thingy for the TBI cars? I thought everyone in the club besides me was TPI? That would be nice.

I am def. gonna try and make it, but its just a long drive, lotta gas, and unknown weather.

RBob

iTrader: (1)

I was thinking about this. Remove the IAT from the connector. Key-on, engine-off.

Then measure the voltage from the black wire IAT connector pin to the engine block. Should be 0 volts (this is the connector for the IAT, not the IAT itself).

Then measure the voltage from the other pin to the engine block. Should be 5.0 volts. If this one isn't 5 volts then there is a problem with either the wiring or the ECM.

The ECM provides a 5 volt pull up to the sensor. The sensor pulls this voltage down to provide a reading. If no SES without the IAT, then the ECM isn't seeing 5.0 volts. Only thing I can think of.

Of course, there can be 5 volts there and the ECM is still bad. That ADC channel may have taken a hit. That is what the scan tool will tell.

RBob.

slow_90firebird

Thanks! I will see if I can find my multimeter, and check tomorrow. Thats exactly the advise I needed.

Soooo... if lets say the 5v wire severed, or frayed and grounded out or something. Then, since the sensor doesent generate power, the ECM would see 0 volts. Are you saying that the ECM is that stupid, not to realize something is wrong?

Hopefully, its something simple that some wire connectors can fix or something. If the ECM is fried, I will just keep driving as is untill I can afford the EBL. However, do you know what the possible effects of having the ECM see the wrong voltage, or no voltage, be? Will that one sensor affect the way the motor runs alot?

slow_90firebird

Alright, just probed the wires. With key on - motor off, the black wire gets .04 volts. The Tan wire gets 4.98 volts.

Now my multimeter might be cheap, however it doesent pick up a random .04 volts from nowhere. I definately tried it about 4 times and each time it came back the same. However, would this be such a small amount, within tolerance for error?

RBob

iTrader: (1)

Those readings are OK (close enough). The ECM will detect if the wiring is open (input goes to 5 volts), or if the wiring is shorted to ground (input goes to 0 volts). These are at the extreme ends of the range which is how the ECM knows that there is a problem. The reading shows that the pull up is OK, and the input wire doesn't have a partial short to ground.

I wonder if there is something else involved in the malfunction routine that is holding off the error. The next step would be the scan tool to see what the ECM is seeing for the IAT value.

RBob.

slow_90firebird

Do any of the major chain stores sell an ALDL cable? I have a laptop, and could download the program. I just need the cable to go from the ALDL to a USB 2.0 port.

Also, when I was doing the multimeter check, I tried unplugging the CTS near the water neck. The motor wouldnt even start. Then I plugged it back in, and it cranked forever. Finally I smelled gas, and saw smoke from the TB. I cranked it again with WOT, and since that kills the inj. it started up, rough, with a black cloud of smoke out the pipes.

Then, I unplugged the vacuum line that goes to the MAP sensor. The car started rough, poured fuel for like 5-10 seconds at a very low idle. Then, leaned out and idled up, and the SES light came on at the same time. So, pretty sure the SES programming is intact.

RBob

iTrader: (1)

For WinALDL:

http://winaldl.joby.se/

For a cable try www.moates.net for the ALDU1 & CABL1 combination:

http://www.moates.net/product_info.p...roducts_id=127

To clarify the malfunction code routines, there are other parameters that need to be met before actual test is made. I looked through the ANLU hac to see how it was coded up. Note that the parameters I list may be different for your vehicle.

Before the IAT lo malfunction is tested the engine needs to be running for 5 minutes. The vehicle speed then needs to be below 35 MPH. So short drives won't set the light. And if driving over 35 MPH it won't set the light.

RBob.

S105.7

i've got one of those serial connectors, but my laptop didn't have serial, so i had to buy a usb-serial adapter. anyway, if you do end up at the meet, i'll have that and my USB link. we can figure out whats going on in this thing. if you want my homemade unit, its yours.

if your ECM is in fact NFG, look into the '427 PCM. there was a guy selling a bunch on e-bay. i got mine for $30 shipped. -Jim

MiScHiEf

Hey,

when i did the open-element mod to my 88 formula tbi, i had to unplug or should i say "unscrew" the IAT sensor, and move it somewhere away from hot metal etc, no codes for me? let me just say that mod is easy and amazing.