(Cross Posted from Prom to see if I can get more input)

I converted from TBI to the Edelbrock MPFI. This included swapping from a 16164631 ECM to a 127747 truck ECM.

Ok, so the first issue we found was that the intake had a major vacuum leak contributing
to the idle problem. We reset the intake today hoping to clear this up once and for all but another odd bit keep coming back. The system keeps (seemingly) destroying IAC's.

The original one died, then I replaced it with the one from the Holley 670cfm TB, then it died, then I went and bought one and it worked for about 3 seconds then went static and died.

When I made the conversion, Troy at Howell had me switch D2 and A11. But when I cross
referenced those two from the FSM schematic, to the 7747 pinouts scanned in on diy-efi,
I switched them back. Heres what happens (problem occurs with the pins swapped or
not):

I turn the car on and it idles for about 25 seconds at 1100rpm. Then it starts surging
between 1300rpm and 1900rpm. If I crank up the manual idle screw to about 2000rpm it
idles steady, but obviously WAY too high. I replaced the IAC (it died, no movement at all), then I replaced the O2 sensor (minor improvement). So I'm kinda stumped.

I rechecked and the 4 wires from the IAC and they properly go to C3, C4, C5 and C6. So it isn't miswired. I'm not getting any codes or a check engine light. So I'm not sure now.

Anyone ever heard of an ECM eating IAC's? Could my 7747 have gone bad from me swapping D2 and A11 (both are sensor grounds, MAP and TPS)? And would that cause the ECM to wig and turn to the dark side?

Help Me Obi-Wan, Help Me Obi-Wan....

Any thoughts?

Kelly 'GhoSSt' Rosato

 

kelly it's good to see you on here, it's been a while. no idea about your problem, way over my head, but i'm sure vader would think it's childs play. might want to post on the prom board tim is way sharp on this sort of thing. good luck

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ICON Motorsports
1st & 3rd

 

I discovered, through my involvement with a friend's misguided and ultimately unsuccessful and self-destructive attempt to create a performance vehicle using a Holley TBI, that the Holley IAC motor is not wired either the same as a factory one, nor the way its manual says. Check it with a meter and a source of battery, and hook it up the way it works, not the way it says you're supposed to. He learned his lesson after the 4th or 5th IAC.

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"So many Mustangs, so little time..."

 

I would agree had I not lost 2 GM type IAC's as well. My Haynes doesn't really go into how to check and see if an IAC is any good. Anyone know where I can get that info?

Kelly 'GhoSSt' Rosato

 

GhoSSt,

Perhaps if you had a little more room in your garage, you could find the problem more easily (a.k.a., I still have space for a blue 'F' body in my garage...)

I have some connection data on the Rochester IACs in the home office. When I return there later today, I'll try to assemble some data and send it off to you.

P.S. - Good to see (hear - read) you're still with us!

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Later,
Vader
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"I cannot take this any more... Saying everything that I've said before..."
Adobe Acrobat Reader 4.0

 

Whats really sad is that the Firebird is sitting out in the one car garage with cat prints all in the dust, waiting for me to find time to rejet the carb.

BUT, with spring comes new hope "USE DA SCHWARTZ". I'll be dropping a 4 car garage, with heated floor and a 9,000 lift. Bathroom, parts washer, 80gal air, all the big boy toys. I literally have to schedule the demo and truck for the old garage and garden shed in the new 3 weeks. So after that I have to get cracking, Impala needs my attention (failed GMPP HOT cam) and the Firebird needs tuning and in there I need to fix the Caprice and get the garage built.

Thankee man. Just been busy and this swap has been a nightmare. The phyiscal part was ok, but dealing with finding these minor vacuum leaks and getting a good chip from Howell is just time consuming. At this point, the IAC's seem to be working again after resetting the A/B jumper, but the tables are just too rich for the IAC to compensate for so it goes static in the locked back position.

Kelly 'GhoSSt' Rosato