My darn SES light turns on immediately with engine startup. I cannot check for codes because my Auto Xray will not scan. I've tried grounding the ALDL diagnostic terminal also and the SES light will not flash any codes.

I have checked the new 749 ECM and it is functioning properly. I have triple-checked the 730-to-749 repinning and it checks out also. The engine runs fairly well. Has anyone who's performed this conversion experienced a similar problem?

 

you should be able to ck sensor values and I think you might have a dead or disconnected one. If your SES light doesn't blink once really fast then stay on(key forward/engine off), your prom chip is faulty.

 

Sounds like a checksum problem in the prom. I have had the exact same problem before but on the '730 ecm.

 

I made my conversion harness so that I could go back and forth between the 730 and 749 pinning easily, simply by plugging a male 15-pin D-sub connector to the appropriate female 730 or 749 connector. In 730 "mode", the engine runs perfectly, including the ability to scan. Therefore, I doubt it's a bad sensor. I have not ruled out the possibility that the PROM (hardware) is bad.

On the other hand, I've heard about this checksum. Okay, I performed a search on "checksum". According to Traxion, "Everytime you modify a BIN in TunerCat and save it - TunerCat recalculates and updates the Checksum stored with the BIN." Well, I'm using TunerCat, so can my problem still be due to checksum?

Willie

 

The "blinking" ses light routine will tell you. FYI, there could be other reasons than the checksum. The chip could just be bad....

 

The problem is the SES light does not blink. It turns on and stays on steady. I cannot link with my scanner, nor does grounding the diagnostic terminal show codes (blinks).

It may be a bad chip. I might burn another and try it just to see.

Willie

 

Try using the 749 as a 730, using the 730 memcal/chip. It's missing a quad output driver so some of the emmisions stuff won't work, but it should run chipped as a 730. This should at least verify the ECM is okay.

It's also quite possible that you may be out of range sensor wise using $58. It could be in spec as a 730, but the code spec limits may be different. (My guess its IAC related). Bob

 

Bob,

I did exactly as you suggest. I ran the 749 ECM with a 730 chip, pinned as a 730, and 1-bar MAP. It ran perfectly fine. I was able to scan also.

I've read a few posts on this board about the IAC repinning and that sometimes repinning isn't necessary or that it's different??? Is this what you're referring to when you say the sensor might be out of range? If so, how can you test/verify?

I had one more thought. Could it be the 2-bar MAP? This is the only sensor I swap.....

Willie

 

Cool, the ECM is fine.

The IAC seems to be the biggest bugga boo about the whole swap. What worked for me, may not work for you. This is because the IAC motors differ from year/type. They all work the same, but the pinouts differ. Mine is wired as a 165 MAF, and works fine. You can try and swap the IAC leads and see if the SES light goes away. Whats happening is if the IAC leads are incorrect, the IAC is running all backwards from what the ECM is telling it too.. finally setting a flag. If you had a cable handy the IAC counts would be the tip off. At idle counts shold be fairly low.
Without a scanner, its all just a guess.

Are you using the 2 BAR with the $58? Or are you using the 1 BAR? You can use either depending on how you set up the bin. Bob

 

Yes, I am running the $58 with the 2-bar. This is when the problem occurs, regardless of whether I'm using the 730 or 749.

When I use the $8D with the 1-bar, I have no problems with either the 730 or 749.

I'm thinking about reburning the $58 code with the VE tables from the $8D and retaining the 1-bar for both PROMs. Hopefully by eliminating one unknown from the equation (possibly a bad 2-bar MAP), it will help solve this problem.


IAC stuff:
I'm using the stock 1987 IAC for the 165. With my MAF-to-SD conversion box set for 730 pinning, all the IAC connector pin designators (A thru D) correspond to the 165:

A = E3 (730) = A Hi = C5 (165) = A
B = E4 (730) = A Lo = C6 (165) = B
C = E5 (730) = B Hi = C4 (165) = C
D = E6 (730) = B Lo = C3 (165) = D

According to Clint's IAC repinning for the 749:

D = E4 (749) = A Hi = C5 (165) = A
C = E3 (749) = A Lo = C6 (165) = B
A = E6 (749) = B Hi = C4 (165) = C
B = E5 (749) = B Lo = C3 (165) = D

The IAC connector pin designators here are from the Sy/Ty schematics and, as shown, are different from the 165 and 730 (which are both the same). My conversion box when set for 749 pinning takes this difference into account. So in essence, am I not pinned as a 165 MAF?

Willie

 

Try and run the 1 BAR with the $58. Just flip the flag in the bin.

Try a different IAC pinout and see what happens.. it won't hurt anything. Bob

 

Thanks Bob. I'll flip the flag and I'll experiment with the four IAC wires. Let's see, four wires / four connectors = 24 combinations!! This may take a while.... Wait! I've tried one>> 23 combinations to go!

Willie

 

Just try unplugging the IAC. I don't think it's the IAC. Wired as a 730, it will just not work, it shouldn't cause a short or anything that would keep the ECM from working, other than not idling correctly.

Here's the pinout I have, from GM documentation:

730
pin ckt Desc. ECM pin Color
A 441 IAC coil "A" Hi E3 Lt Blu/Wht
B 442 IAC coil "A" Lo E4 Lt Blu/Blk
C 443 IAC coil "B" Hi E5 Lt Grn/Wht
D 444 IAC coil "B" lo E6 Lt Grn/Blk

749
pin ckt Desc. ECM pin Color
A 441 IAC coil "A" Hi E6 Lt Blu/Wht
B 442 IAC coil "A" Lo E5 Lt Blu/Blk
C 444 IAC coil "B" Lo E3 Lt Grn/Blk
D 443 IAC coil "B" Hi E4 Lt Grn/Wht

So, they Switch coil A with coil B and reverse the polarity of B. Make sense that it would work that way if you've ever worked with stepper motors, but I have no idea why they changed it so much. I thought these were the only 2 combinations they used, but I see a couple others, but I think they just switched ABCD for DCBA. Strange if ya ask me! Must've been to keep people from doing such swaps so easily, without issues?????