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Old 08-18-2012, 09:10 AM   #1
Larry
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TBI prom tuner needed

Does anybody know of a good tuner for older TBI PROMS? This past winter I swapped in a TBI 7.4L in my FIL’s 1993 C1500 Sportside. I modified the stock 4.3L harness to work with the 7.4L components and used Howell for the PROM tune. Now, I’ve had nothing but good luck with Howell on past projects but after 3 different PROM tunes I still don’t think they have this thing calibrated correctly and looking for alternatives.

The truck runs great! We’ve put about 2,000 miles on it and it has tons of smooth power through all ranges, it will smoke the tires like mad but the problem is it likes to die when coming to a stop. It does not drop a SES light nor leave codes. I’ve swapped in known good IAC motors and just about everything else. Fuel pressure is spot on at 12 psi. I am convinced they have it programmed as an automatic rather than a manual transmission. I am confident there is not a sensor issue, air leak or anything else with this engine. It has to be an outright calibration issue. They did add a “hot tune” that I would like to get rid of as my FIL is complaining about the rich smell at idle as well.

I am running a 1227747 ECM. I have an extra PROM but need a stock tune for a 1993 7.4L with a manual trans and 3:08 gears. Looking for a good alternative to Howell. Anybody got any suggestions? This truck is just a city cruiser driven by a 70 year old man, not a hot rod.



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Old 08-19-2012, 09:32 AM
Posted in reply to Larry's post "TBI prom tuner needed"
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I always suggest a hands on tuner in your area. If that is not possible then data logs are a must for proper tune or it's just a starter tune.

Smelling rich at idle is normal if Cat was removed, your nose is a horrible AFR meter. If starting up in garage again normal without cat and worse during warm up.

Auto to manual bin if that is the case won't help idle. The other way would if it were auto

What's done to motor?

Totally warmed up what is idle RPM? Vacuum reading?

Can you record data? Without data it is impossible to tune out issues like this. Can you get IAC counts at idle?

4.3L to 7.4L? Did you swap two wires on IAC? C5 Green(or Blue) w White stripe goes to B on IAC, C6 Green (or Blue) w Black Stripe goes to A on IAC for all small blocks, they are reversed on BB...
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Old 08-20-2012, 01:24 PM
Posted in reply to eagle mark's post starting "I always suggest a hands on tuner in..."
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Thanks for the info Mark!

There are no hands on live tuners in this area that I know of. I don’t see why a stock 1993 7.4L wouldn't work. Maybe part of the problem is Howell has this thing running rich as cob with their so called “hot tune”. Probably why it runs like a rapped ape at WOT and lugging at low RPM’s in high gears…like going 30 MPH in 5th gear is no problem for this truck. It still pulls hard in 5th gear from barely crawling up to 60 MPH.

My ’89 Suburban with a TBI 5.7L sans a cat does not smell rich or burn your eyes although my 8.1L in the K10 does smell pretty fruity, but it is running a “HP tune” and about 5 lbs higher fuel pressure over stock.

The 7.4L in this Sportside is bone stock other than an Edelbrock intake. The truck doesn’t live here but from memory from a few months ago when I did this work, the idle is around 850 (maybe even less…I can’t remember…none the less the idle felt good) once it goes in to closed loop. In open loop it idles stupid fast like around 1,500 RPM, which I don’t like. This too feels like a calibration issue.

I don’t recall what the vacuum reading was but at the time when I installed the engine and working out other bugs the vacuum reading was on par with what was outlined in the 1993 GM C/K service manual. I do have an OTC Tech 2 but can only take snap shots rather than full on recordings when monitoring an old OBDI vehicle. The IAC counts were on par with the service manual and I confirmed it was working properly as I ran though the strategy based diagnostics in the manual. Even the MAP readings are right on the money.

But you bring up an interesting comment on the IAC wiring. I am actually using Howell’s adapter to convert the IAC from the square plug on the screw in type IAC (4.3L harness end) to flat 4 pin connector on the big block TBI units flange mounted IAC. I did not repin anything as Howell checked the pinouts and said all matched up although I did have to step up from a 16144288 ECM (original 4.3L ECM) to the 1227747 ECM. As I mentioned, IAC counts on the Tech 2 are on par with what the service manual calls out and its operation works as the strategy based diagnostics in the manual state. It just seems like it the IAC is too slow to catch it from dying when coming to a quick stop. I’ve tried two other known good IAC motors I had laying around with no change. Maybe that is one thing I need to go back and double/triple check again are the pinouts but still odd that IAC counts are spot on.

I have a hard time believing there is something pined wrong or a parts compatibility issue. It just feels like an outright calibration problem. This is far from my first fuel injection engine swap project but been the most challenging getting the bugs worked out. I am about ready to toss this TBI in the garbage and find a L29 MPFI intake and convert it over to a P59 ECM running OBDII and MAF. Damn thing is pissing me off and I am getting tired of hearing my FIL complain about it.

I have Tuner Pro for programming Delphi MEFI4 ECM’s. I ran my 8.1L on a MEFI4 for the first year and could never quite figure out how to program it correctly by myself. The tool is great but much better if the user knows that they are doing. I do not know what I am doing when it comes to actually tuning your own ECM. I ditched the MEFI and went to a P59 ECM/ MAF, etc and never looked back.

Thank for your input! If we were closer I would bring it to you.
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Old 08-20-2012, 05:04 PM
Posted in reply to Larry's post starting "Thanks for the info Mark! There are..."
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If the motor is that stock and has BB injectors turn the pressure down to 13, disconnect power to ECM and retry.

Also check IAC counts at idle and when reved up, they should go up when reved. If motor is starting to stall they should go up.

Hot tune is just a name so people buy it. I can set up one chip to run better then a stock truck with more power and MPG. More power available from WOT and still throw in Lean Cruise. MPG increase only works if you keep foot out of WOT!

If you can datalog with TunerPro and burn chips I could help? Or at least look at the log for you...
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Old 08-20-2012, 06:26 PM
Posted in reply to eagle mark's post starting "If the motor is that stock and has BB..."
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It does have new injectors for a ’93 spec 7.4L from Napa (12 PSI…not the 23 PSI injectors like used in ’94 & ‘95). The fuel pressure is at 12 psi now when measuring pressure at the fuel filter so there is no need to turn it down to 13??? Not sure if you saw the fuel pressure in my first post or mis-typed.

When the truck comes back to my house I’ll check the other stuff. I’ll see if I can get any data on the Tuner Pro software. If I remember correctly, the cable I have to connect to the MEFI-4 ECM is the OBDII shape where it won’t plug into an OBDI type plug (don't forget, my TunerPro is for MEFI-4 RamJet and Marine ECMs) but I’ll check to see if it will work on this old dog.

As I mentioned, the IAC operates correctly by following the diagnostic aids in the GM factory service manual.

Thanks!
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Old 08-20-2012, 07:41 PM
Posted in reply to Larry's post starting "It does have new injectors for a ’93..."
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Ah, that was your truck the pressure was turned up.

Yes you'll need an OBDI cable. If you do this let me know, I have written a XDF and ADX file for TunerPro with all the bells and whistles.
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Old 08-20-2012, 08:27 PM
Posted in reply to eagle mark's post starting "Ah, that was your truck the pressure..."
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Larry, there is a guy in Denver who does GM chip.burning.

I need to dig through some old records and find his contact info. He is always at the local swap meets handing out business cards
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Old 08-20-2012, 09:07 PM
Posted in reply to 63chevyll's post starting "Larry, there is a guy in Denver who..."
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Mark,

Yeah, it is the 8.1L in the other truck running high pressure. Sorry, throwing a lot of info out there that gets confusing.

Brad,

Let me know if you find that guys in name. The in-laws are leaving for their place in FL shortly for the winter so I’ll be babysitting the truck from October until they get back in April.
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Old 02-06-2013, 09:59 PM
Posted in reply to Larry's post starting "Mark, Yeah, it is the 8.1L in the..."
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Update on this little 2wd project. As I mentioned this truck is my father-in-laws and the in-laws spend half their time in CO and FL. I’ve been babysitting the Sportside since they left in October and with only 30 days until they get back I figured I better get back on this thing to address the dying issue when rolling to a stop before they get home. I suspected all along the issue lied with the calibrations as I was never confident of Howell’s PROM programming while I did feel confident with the wiring and sensors I when doing the engine swap last winter.

Well, a friend turned me on to Harris Performance (tbichips.com) and I called them week before last and explained what the truck was, which ECM I am using and what is it in the truck now (including the L29 Vortec cylinder heads). The PROM showed up in the mail last Friday which I toss in on Saturday. I could tell the minute I fired it up after installing the new PROM it was running much better. Even the cold open loop idle was smoother with a lower RPM idle speed (before it would idle at 1500 RPM when cold). I’ve got about 200 miles on it now since installing the new Harris Performance chip last Saturday and the dying problem is gone! In fact, it just all around runs better. The acceleration is smoother, the up and down of the RPM range is smoother when shifting, no more bucking when shifting, etc. The excessive "rich" smell is gone too! The truck finally runs like a healthy big block with a little truck body bolted around it now.

I am not by any means slamming Howell Engine Development, as I have had nothing but good luck with them on previous EFI swap projects and will be using them again on the 8.1L swap into the Suburban. Not sure why they couldn’t seem to get a properly tuned PROM for this truck done right in 3 attempts though so I had no choice but to try someone else. Maybe their 7.4L edit tables are corrupt or something

End of story….the powertrain in the little 2wd Sportside 454SS clone is done! I wouldn’t go as far to say this truck is FAST in the new world of fine running sequential port injected LS engines, but by 1993 standards this little truck hauls ass. It would probably give an 80's TPI Camaro a run for its money though

My only regret with this project is using the Energy Suspension engine mount inserts. Those mounts are a bit too stiff for a truck like this where you can really feel the engine. I used those same mounts on my K10 with the 8.1L where it feels smooth as silk at idle and throughout the RPM range. Not sure if the firing order between the 7.4L and 8.1L are that noticeable with harmonics or what the heck. GM did change the firing order on the 8.1L for the sake of smoother operation. Maybe that little bit of difference makes a big difference when it comes to using polyurethane mounts
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Old 02-06-2013, 10:11 PM
Posted in reply to Larry's post starting "Update on this little 2wd project. As..."
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Oh, here is the truck. It is kind of a sleeper




And it sounds soo sweet with this exhaust


Engine mount regret
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