ImpalaGuy

Hi guys. This is my first post. I've been searching this forum a LOT over the last week -- man you guys have been busy over the years. All this ECM info tucked away in a third gen forum. Anyway...

I've running the '7427 ECM in my '95 truck ($0d mask). I'd like to put MPFI on it, somwhat because I'm going to a better cam/heads/headers and the TBI is a bottleneck, but also just because it's a cool little project.

I've done my homework on the edelbrock TBI-to-MPFI kit -- using 4 sat injectors on each '7727 driver, and think the general idea may work but I'm unhappy with the restrictive intake they ship with the kit. So I'm looking to do my own. I'm running vortec heads and have come up with two intake combinations:

1. Holley vortec intake 9901-107. This is a single plane with EFI provisions. I would gut my stock TBI and put it on an adapter, similar to what edelbrock did. Shouldn't be too terrible to tune; perhaps some concerns about low-end torque with the single plane though.

2. Holley stealth ram vortec. This is where my question is headed -- I would have to run either a TPI or LT1 throttle body. Now I realize the general concepts between the TBI and LT1 TB's are the same (IAC and TPS), but has anybody actually tuned one with a TBI ecm?

I intend to do my own tuning. I've done a few cars, so I can stumble around in that area, but I'd like to know if anybody knows of any immediate pitfalls before I spend $$$ on any intakes. I saw a few posts about people running two ecms -- one for tranny and one for tuned port, but I'd like to stick with one -- the '7427 can do both, is well documented and is 8192 baud.

All comments are welcome -- your thoughts?

Ron

JPrevost

Well if you're set on converting over then I'm sure that pcm will run the engine but I don't know how much tuning would be involved.
If it doesn't pan out then you could always use the pcm for the transmission and a 7730 for the fuel.
I haven't heard of anybody using that pcm on PFI but from the hack bit 0 of byte at location 400B has this as an option. I bet you just set that and go with option 2. No real reason why it shouldn't fire up .
Option 1 would work nearly identical only cost less, not sure if you care much about the apperance or not so it's kind of up to you. Personally for a truck I'd go with option 1 seeing as it's the least expensive but I don't know your cam/heads package so it's hard to say.

ImpalaGuy

Thanks JP. My biggest concern with using a TPI/LT1 throttle body is the IAC. A single step may let in different amounts of air compared to the TBI, the result of which could be an oscillating idle, or worse no idle at all. Or even worse it won't even drive that stepper motor. Also I don't know the difference between LT1 and TPI bodies. If anybody has any experience or insight on those issues I'd much appreciate your comments.
Yes I saw that in the source hack on Moates site. I'm sure I'll try setting it whichever intake I choose, but I would feel better trying it on a test bench setup, which I don't have.

Also I'm a bit apprehensive of that hack. Somebody certainly put a lot of time into it, but poking through it I see that location $0062 is labeled as the fuel pump. But from the rest of the code it's kind of obvious that location is rpm/25. Anybody else notice this?
Actually #1 would cost a bit more. The vortec stealth ram is a steal IMO at $320, but the other one robs me of $450. Why it's that much for a simple single plane intake with 8 extra holes is beyond me.

I suppose I should have given you guys more info on the heads/cam. Heads are stock vortecs with a moderate port job. Hopefully enough to flow better but not enough to kill my low end. I'll be running a cam from a ZZ4 crate engine: 208/221@0.050 on 112. I tuned that cam in an LT1 so I think it will be okay. Also 1 5/8" long tube headers (cheap ones, like flowtech) will be in the mix.

Also if anybody knows any other MPFI intakes for the vortecs I'd be glad to hear from you.

Ron

Z69

RamJet

ImpalaGuy

Yes you're right. I forgot to mention that one, but at $1500 it may be worth forgetting.

ben73

I am currently running a '8625 PCM which is nearly identical to your '7427. I have it running TBI at the moment, but am looking into using it to run PFI mode also.

I did once change the TBI/PFI flag while the engine was running (ostrich), and nothing change, the inj. PW stayed the same, as did everything else as far as I could tell, so I suspected there was more to it...

Just 2-3 days ago I stumbled across this post on another forum, read the posts by "Half Ton Rat". He says he has done it before with a '6395 (the other member of this group of near "identical" PCM's). He mentions a mod using a soldering iron.... I emailed him to get more info, but have not yet had a reply..

Here is the post, they are mostly refering to the edelbrock tbi-pfi conversion kit, which as far as i understand uses a PCM from this family..
http://www.fullsizechevy.com/forums/...9&page=2&pp=20

SATURN5

Differences between TPI and LT1's vary by years. At least two different cabling styles on TPI's and I believe at that same goes for LT1's.

I have got both TBI's and a TPI TB here. The IAC valves themselves look to be identical. If I get a chance later tonight I'll measure them up.. But first.. oil change on the van.

va454ss

iTrader: (1)

Try contacting Ken at HPTuners.

ImpalaGuy

If there's any change with that switch, it *could* be to move the injector pulses from once per spark to once per crank rotation. The pulse width per cylinder wouldn't change. Just a guess on my part. An ecm bench and scope would clear up that pretty quick. I've got a scope, but no bench. Wish they would make another run of boards.

I just read through that post, but as you mentioned there's not much meat on the TBI/PFI switch. Let me know if you get a response from him (BTW "HalfTonRat" on that board is Ken from HP Tuners). I tried contacting him as well.

ImpalaGuy

I called Holley this afternoon. The tech guy said that the stealth ram requires and LT1 throttle body. The TPI IAC motor will interfer with the water outlet. So now I'm on a quest for an LT1 throttle body. Know anybody?

Did you have a chance to measure out the IAC on the TPI? I'm still curious as there's a good chance it's identical to LT1.

Just the sheer challange of it is making me want to get the stealth ram. Plus the wow-factor of raising the hood of yet-another-TBI-truck and seeing that thing.

Man I can talk myself into anything...

JPrevost

This is just a guess but GM has a trend of using async on wetflow TBI for the AE, maybe switching that bit turns off the async and just adds the AE to the sync pulse width. If I had an electronic trans I'd be more into this pcm but for right now I've only fiddled with it on a stock 95 suburban... not much you can play with when the engine is so slow to respond.

ben73

I just received an email back from Ken. He says he will send me the info in a few days.

HaulnA$$

I got the info from Ken a while back after about 4 months or more of waiting. Interesting stuff. I have been researching this project on and off for about 8 months now and will hopefully testing out some injector timing stuff on my nearly complete PCM test bench soon. I had to put the project on hold for a while due to my recent marriage but I am back at it hard and heavy. As pointed out before, the $0D mask has PFI routines in it and has been used on 4 cyl. PFI S-10's. I will post my results and would love some company in the project. I would be willing to share the tidbit of info that I got from Ken. Contact me off line. HTH

ImpalaGuy

I'm interested in what he had... PM or email me. I'm also in the process of making my own ecm bench so test these things out. It may take me awhile though.

Oh and per my original post, I've decided to go with Holley Stealth Ram. It's a bit cheaper and has a lower power band than the single plane, plus it gives me a chance to see how the '7427 and the LT1 throttle body play together.

HaulnA$$

ImpalaGuy, I'll contact you. The stuff from Ken is actually for the $0E mask, but the $0E, $0D, and $31 masks are so closely related that it can be made to work for any of them. I actually have 2 projects in the works that relate here. The first is a mild (approx. 350 HP) 350 with a Ramjet that will have a 4L60E controlled by a '7427 and go in a '71 C10. After I work out all the bugs, I have a full fire breathing stroker that should hit 500 NA HP with a Holley StealthRam that will mate to a 4L80E and go in my '94 C1500. Again, the '7427 in control. I already have fan control and/or nitrous control patches worked out on paper. I just need to finish my PCM bench so I can test it. I cannot tell you how happy I am that others are now showing interest in this. I need the help as it is a big project for one person with a family and little time but lots of ambition. Also, I designed my own PCM bench and have the schematic. Once I get that finished and debugged, I would be happy to share that so as to keep the project moving forward quickly. No sense in re-inventing the wheel. HTH

SATURN5

Holley isn't entirely correct. My TPI TB fit just fine, however I had also had prior to using the stealth ram, cut down the IAC/TB heater housing, removing all material not related to the IAC. Frankly I say it would fit outright, and Holley is just C.T.A. (covering their a..).

Nope, sorry, we've had the wonderful pleasure of strep throat this week, thankfully I've so far come thru unscathed, however I've been busy with house stuff, I'll try and do that tomorrow. lol.

ImpalaGuy

No sweat. It's a stepper motor so I'm not sure what you'll be able to measure anyway. I'm more concerned that that the steps counts will be different causing crazy idles or serious code work.

Ron

RBob

iTrader: (1)

I gotta' come up to speed on these new(er) fangled ECM/PCM's. . . Looking at the $0D stuff the CPI/PFI vs. TBI option bit is used to setup the hardware differently. Also looks to be used for when the code switches in and out of sync/async fueling modes. Interesting stuff. There also seems to be the ability for the ECM and code to delay injector relative to the DRP pulse (now where have I seen that before ).

RBob.

ImpalaGuy

Yes I saw those-type-things in the hack from moate's site, but can't say I understand what's going on yet. This could end up being very interesting. This pcm has a lot of potential: 8192 baud, tranny control, source hack with a lot of work done, and port injection (possibly).

Hauln forwarded me an email from Ken at HPtuners. It looks like he got port injection running on a 502 engine and sent us the bin along with a modified tunercat tdf. Haven't had a chance to look deeply at it yet.

I'm definately going to have to have an ecm test bench for this work. I started mapping all the inputs/outputs and how to similulate them, but I know I'm doing work that's already been done. Can somebody send me the schematics and parts list for the ecm board that was group purchased around here? Even better would be if somebody had a board they wanted to sell -- I know I could get it to work with this pcm.

Ron

RBob

iTrader: (1)

The programming of the hardware for TBI vs PFI makes sense. A TBI setup will alternate injector firing on each DRP. IOW every DRP fires an injector, alternately between the two. On a port setup in the typical double fire mode all injectors fire at the same time once every engine revolution.

Not sure what they are doing with the sync/async stuff, didn't look at it closely enough yet.

RBob.

SATURN5

I'm sorry but the schematics are not public domain. Also, I'm currently not looking to do a run. Just too many other projects going on to oversee it. However I'll happily send you a parts list.

However there is public domain info on building a ecm bench.
diy-efi had info available.

HaulnA$$

Come on in, the water's fine. There is a lot more cool stuff in the $0D, $0E, and $31 code besides CPI/PFI like several spare inputs and outputs to play with and more. The PFI code also requires a mode change via the Netres to set up the hardware. So do tell RBob, where have you seen injector delay relative to DRP before?