TPI Backwards Idle - Need Advice

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12-04-2013
66 C10 383

TPI Backwards Idle - Need Advice

I'm getting ready to drop a 383 in my 66 C10 truck and wanted to reinstall my 89 MAF based TPI on it. Last time I used this unit was over
6 years ago and wanted to address a problem I couldn't get sorted out last time it was in use.

It idled exactly backwards. First start up it idled at about 700 - 750 rpm. Instead of idling down after a few minutes, the idle would
raise to about 1100 rpm and stay there until the eng temp went back down. Otherwise it seemed to run good.

After much advice, I switched the 4 wires going to the IAC and nothing changed. I think I even changed out the IAC for a new one with
no change. Never could get it figured out as the engine broke a ring and needed pulled out.

My setup consisted of a Howell TPI for a g-body that was in my 84 Cutlass and was running an Ed Wright chip for an 89 MAF.

The engine has been rebuilt with more compression and cam so I had PCMforLess burn me a chip for initial start up. I also plan on
buying a new harness for the C10 since I'm not sure if the Howell harness is/was the problem.

The whole system is basically stock TPI with the following upgrades. Accel SuperRam plenum, Accel base, Holley 58mm tb., started out
as an 87 TPI setup but switched to 89 for 9th injector elimination. I'm also running a Holley afpr.

Engine specs at the time were 383 with AFR 190 heads, Comp hyd roller 118* 224* on 112* lsa, 1 5/8" headers, 9.5 comp ratio. T56 trans.
Same basic engine with the following mods. Compression raised to 10-1 and cam is now a Comp hyd roller with 230* 236* 113* lsa
(XFI 280 cam).

One other question, is a knock sensor module differant for a 305 & 350? I know the sensor itself is differant. What would happen
if I used a 350 sensor with a 305 module?

Thanks for any help you can give.
Doug
12-04-2013
EagleMark

PCMforless should really help you with tech support since you are their customer? What do they charge for a starter chip nowadays?

5.0L and 5.7L knock module and knock sensors are different. If they don't match they don't work right.

No reason to buy another harness, there's only four wires to trace pin to pin to see if they are wired properly. Switching all four wires puts you right back to where you were. I've seen this before with TBI and the SB to BB are wired differently. Just switch 2 wires and the IAC should start commanding the proper direction.

This is if there is not a mechanical issue like vacuum leak created by warmed up engine causing it? You should really have a data logging cable by now to see things like watching IAC count to verify what is happening. You'll also need a cable to do data logs and get your chip fine tuned!
12-04-2013
66 C10 383

Thanks for the reply Mark, I was hoping you would chime in ... LoL

PCMforLess now has 2 branches, the branch that does the tuning is in NC. www.pcmofnc.com/ They charge $139 for a stock engine with an added $45 for heads/cam or $65 for a stroker engine which is the one they did for me.

In reference to my question, I have their chip but it presently has not been used yet as it was tuned for the new engine combo that has not been fired yet.

This is all from memory and over 6 years ago. I have no way of checking anything as the engine is not in the truck yet. I was asking these questions to try and sort out any problems I may have when I get this up and running again.

I did try switching the 4 IAC wires while I had it running but the idle still did the same for some reason. I switched the 2 low idle and 2 high idle wires in the connector and nothing changed which I also thought was odd (no change).

I was considering buying a new harness for 2 reasons. First and foremost is the possibility that the problem is in the harness. It might be elsewhere I know. This same harness also had a problem throwing a code 42 which was eventually traced to a bad connection on the KS module wire. The second reason is the harness has the ip connector that plugs directly into the g-body whereas the truck dash does not have. I contacted Howell about how to add this harness to my truck and they basically said when I got ready to put it in my truck they'd help me then ... I'd like to get the harness ready before I install it in the truck. I may also need different wire lengths etc.

To help cut down on problems ahead of time and cut down on possible problems, I plan on replacing most sensors so I'll make sure to get all 89 sensors and replace the KS module to the correct 350.

Thanks!

Doug
12-04-2013
EagleMark

I could see starting with a new harness then for a new project. :rockon:

I forget which two wires but when I ran into this issue with a aftermarket harness... :rolleye: I did this little write up. I would not do it running though as the IAC resets when key is off. So it would have to reset, then start to do it's thing. Did you try another IAC? Seems like I found a couple in last couple years that checked out just fine but had issues. Curiosity mad me tear them apart and I found they were stripped in one spot and just spun...
http://www.gearhead-efi.com/Fuel-Inj...nd-Small-Block

Quote:

Originally Posted by 66 C10 383

PCMforLess now has 2 branches, the branch that does the tuning is in NC. www.pcmofnc.com/ They charge $139 for a stock engine with an added $45 for heads/cam or $65 for a stroker engine which is the one they did for me.

Ahhh! I see... I need to raise my price by $75 to get more work? :laugh:

I have to say though you picked a good mail order company. Of all the companies that I have retuned they are the only ones who actually have a good tune to start with. :thumbsup:

And howell has always made good stuff.
12-04-2013
dave w

1 Attachment(s)

An ohm meter and wiring schematic are the tools of choice to confirm or deny a wiring problem.:thumbsup:

I'm not a huge fan of the MAF TPI system. Years ago the MAF system was favored because it was thought to be the more forgiving TPI system to tune for a modified engine. Years ago the tuning software available for the MAP system was not as developed as it is today. A new MAF or MAP harness would be about the same in price? The downside to the MAP TPI system today is finding a V8 MAP Memcal!

I would like to have seen a data log of the reverse idle. See Monitors pic below.

dave w
12-06-2013
Hog

Quote:

Originally Posted by EagleMark

I could see starting with a new harness then for a new project. :rockon:

I forget which two wires but when I ran into this issue with a aftermarket harness... :rolleye: I did this little write up. I would not do it running though as the IAC resets when key is off. So it would have to reset, then start to do it's thing. Did you try another IAC? Seems like I found a couple in last couple years that checked out just fine but had issues. Curiosity mad me tear them apart and I found they were stripped in one spot and just spun...
http://www.gearhead-efi.com/Fuel-Inj...nd-Small-Block

Ahhh! I see... I need to raise my price by $75 to get more work? :laugh:

I have to say though you picked a good mail order company. Of all the companies that I have retuned they are the only ones who actually have a good tune to start with. :thumbsup:

And howell has always made good stuff.

At one time, the PCMforless guys had an option for a chip and they would retune the chip for 6 months til the chip was right. IIRC it came with soem sort of logging equipement, but I'm not 100% sure on that.

peace
Hog