TBI to 96-99 CSFI

**Daveo91** · 03-16-2022

I've posted this question before, but back then I was thinking of using everything from the donor rig: harness and computer included. Several of the good folks here talked me out of that plan which is a good thing: I don't want to mess with the black box (it's a '97 so not tunable with HP Tuners anyway) and I'm not really wanting to do the swap to 0411. So if I do this I'll stick with OBD I and either use a 7427 with the port mod (I'm running 7427 now) OR (more likely) make the switch to a EBL Flash II. I really like what I've read about the EBL with things like self learning VE tables and hi-way mode. But I do have a 4L80e so I know I'll have to run the 7427 in tandem with the EBL.

But what I'm really posting about here is the nuts and bolts of the swap. Is anyone aware of any write-ups about this switch? This is a 383 with vortec heads in a '91 suburban. I'm currently running the GMPP q-jet manifold for vortecs, with a TBI adapter plate. My specific questions are along these lines:

1. throttle cable looks like it has to be a lot longer, since it wraps around the front of the TB and attaches on PS side, pulling toward front. Just steal a cable from a junkyard '96-'99?
2. Connectors such as TPS, MAP, IAC, etc. I'm assuming I'd have to replace all connectors to get these to hook up? I do have the complete harness from the '97.
3. wiring for the 8 injectors themselves. Probably a dumb question here, but does the wiring for one TBI injector power one whole bank? Or is there a different connection method? Or maybe it doesn't matter since it's going to be batch fire? How do you physically make those connections from one to four?
4. Fuel lines. I'm guessing I'd probably have to have a section of braided steel to get them to connect to the tubes that mount to the CSFI manifold?
5. Fuel pump. Will my Walbro 155 fuel pump be sufficient?

Probably tons of other questions that I'm not even thinking of but answers to some of these will probably help make the decision whether or not I want to go down this path. Thanks!

**1project2many** · 03-17-2022

You will want to have the wiring diagrams for the '91 and the '97 handy. Use the connectors from the 97 harness where needed. It's amazing how many subtle things can be different so plan to take some time during the swap. The fuel needs are dependent on the peak horsepower produced by the engine. 155 lph pump is good for roughly 400 hp. If your engine is close to that number play it safe and plan on a larger pump. The 8 injectors are connected to a very large square connector in the manifold. You will need the matching connector from the '97. Tie the LH bank power wires together and connect to TBI injector power wire #1. Tie the RH bank power wires together and connect to TBI injector power wire #2. Do the same with the ground side wires, tying them to the TBI ground side wires. Think of eight PFI injectors as one TBI injector for this operation. I would use steel line and bend it appropriately so the new lines fit the engine. If you can clamp braided line so it will securely hold up to 100 psi fuel pressure than yes, braided will work. Otherwise you may want to get a set of fuel lines from a 97 and try to connect them to the frame mounted lines under the truck.

**dave w** · 03-17-2022

There is the option to convert the 16197427 to MPFI, please see attached.

dave w

**Daveo91** · 03-17-2022

Originally Posted by 1project2many

You will want to have the wiring diagrams for the '91 and the '97 handy. Use the connectors from the 97 harness where needed. It's amazing how many subtle things can be different so plan to take some time during the swap. The fuel needs are dependent on the peak horsepower produced by the engine. 155 lph pump is good for roughly 400 hp. If your engine is close to that number play it safe and plan on a larger pump. The 8 injectors are connected to a very large square connector in the manifold. You will need the matching connector from the '97. Tie the LH bank power wires together and connect to TBI injector power wire #1. Tie the RH bank power wires together and connect to TBI injector power wire #2. Do the same with the ground side wires, tying them to the TBI ground side wires. Think of eight PFI injectors as one TBI injector for this operation. I would use steel line and bend it appropriately so the new lines fit the engine. If you can clamp braided line so it will securely hold up to 100 psi fuel pressure than yes, braided will work. Otherwise you may want to get a set of fuel lines from a 97 and try to connect them to the frame mounted lines under the truck.

Awesome, thanks! This is great info. I took a closer look at the wiring tonight, both existing TBI and the harness from the '97. Looks like TPS might be the same connector, but everything else is different. Challenging for sure, but doable with time. My engine is HP is probably low 300s so I should be good with 155 fuel pump. Understood on the injector wiring. I can't remember if I saved the fuel lines from the donor rig - I don't think so. I'll come up with something. Maybe I'll grab some at Pick-n-pull and connect down below on the frame as you suggest. Need to get a throttle cable there anyway.

Originally Posted by dave w

There is the option to convert the 16197427 to MPFI, please see attached.

dave w

Thanks, Dave. I have the Word doc and have read that over, but I don't think I've seen the excel file with the calibration mods. That will definitely be helpful if I go that route. I'd like to go with the EBL, but also trying to save some $$ so modifying my spare 7427 may be the way to go, at least initially. I've heard a few concerns about overloading the drivers in the 7427 by trying to run 8 injectors - do you have any experience with that problem?

**dave w** · 03-17-2022

Originally Posted by Daveo91

Thanks, Dave. I have the Word doc and have read that over, but I don't think I've seen the excel file with the calibration mods. That will definitely be helpful if I go that route. I'd like to go with the EBL, but also trying to save some $$ so modifying my spare 7427 may be the way to go, at least initially. I've heard a few concerns about overloading the drivers in the 7427 by trying to run 8 injectors - do you have any experience with that problem?

I've helped with several '7427 MPFI conversions, none have experienced overloading of the injector drivers.

dave w

**1project2many** · 03-18-2022

I've heard a few concerns about overloading the drivers in the 7427 by trying to run 8 injector

Current draw = Volts / Resistance
Resistance for 1 TBI injector = 1.8 Ohms so current = 14V / 1.8 Ohms = 7.8 Amps
Resistance for (4) L31 PFI injectors in parallel = 3.75 Ohms so current = 14V/ 3.75 Ohms = 3.7 Amps

So (4) Vortec injectors should not cause a problem when use in place of (1) TBI injector.

**Daveo91** · 03-20-2022

Awesome thanks! I'll feel more comfortable using the 7427 with the MFPI mod now.

**Daveo91** · 05-02-2022

It took me a couple trips to pick-n-pull , and looking at 3-4 trucks both times, but I finally found the upgraded spider for a 96-99 vortec truck. $37. I think it’s the Delphi conversion the dealerships did. It was pretty greasy from PCV and EGR fumes, but it seems to be cleaning up nice. Of course looks ain’t everything..... Should I:

1. Install it in my conversion project as is and hope for the best?
2. Would it be useful to test resistance across each injector? Is there a range I’d be looking for, or just consistency?
3. send it to Mr. Injector for rebuild/cleaning?
4. Are the individual injectors replaceable? 3C2A9A56-C6AD-47B2-84CD-65433CC55C63.jpg

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D4CA0C37-FCDF-4C0C-A2F8-3A1A7A90471F.jpg

**dave w** · 05-02-2022

Test the resistance yourself.

Perhaps test each injector with about 35 PSI of compressed air and check for leaks by "dipping" the injector in water. This test only determines if the injector is stuck open. Possibly trigger (momentarily with 12 volts DC) each injector open / closed with 35 PSI of compressed air and repeat the water dipping test.

Risk vs. Cost . . . for an "all-in" budget test . . . install the injectors as is.

I think injector cleaning is typically $18 per injector, which is a bargain for two TBI injectors. Maybe $18 per injector for eight injectors is a bargain?

**1project2many** · 05-02-2022

"1. Install it in my conversion project as is and hope for the best?
2. Would it be useful to test resistance across each injector? Is there a range I’d be looking for, or just consistency?
3. send it to Mr. Injector for rebuild/cleaning?"

The injector is designed as a "plug and play" replacement. Fuel delivery and electrical characteristics are the same as the original part, at least as far as the pcm is concerned. You could measure resistance across a few terminals of the old injector then across the new one for comparison. You could install the injector and connect the fuel lines then key on/engine off and let the pcm test the injectors. You would need a scantool to view the trouble codes. Or you could simply install the injector. We've had very few problems with that style injector here so if that were going into my vehicle I'd probably clean the exterior and install it as-is.

**tayto** · 05-02-2022

just so you are aware the 7427 will not fire the injectors sequentially. it only will run batch fire and you will have to wire the injectors accordingly. as far as cleaning injectors, i do it all the time now. recently went to the junk yard to get a set of injectors for a civic and then dropped them off to get cleaned. had to go back and get another set (8 injectors total) just to get a good set of 4 FWIW...

EBL is a cool product, but i don't really consider it an upgrade running it in parallel with the 7427. unless you are running forced induction or some other power adder.

**Daveo91** · 05-03-2022

Originally Posted by dave w

Test the resistance yourself.

Perhaps test each injector with about 35 PSI of compressed air and check for leaks by "dipping" the injector in water. This test only determines if the injector is stuck open. Possibly trigger (momentarily with 12 volts DC) each injector open / closed with 35 PSI of compressed air and repeat the water dipping test.

Risk vs. Cost . . . for an "all-in" budget test . . . install the injectors as is.

I think injector cleaning is typically $18 per injector, which is a bargain for two TBI injectors. Maybe $18 per injector for eight injectors is a bargain?

Thanks, Dave. I'll definitely do some resistance testing!

Originally Posted by 1project2many

"1. Install it in my conversion project as is and hope for the best?
2. Would it be useful to test resistance across each injector? Is there a range I’d be looking for, or just consistency?
3. send it to Mr. Injector for rebuild/cleaning?"

The injector is designed as a "plug and play" replacement. Fuel delivery and electrical characteristics are the same as the original part, at least as far as the pcm is concerned. You could measure resistance across a few terminals of the old injector then across the new one for comparison. You could install the injector and connect the fuel lines then key on/engine off and let the pcm test the injectors. You would need a scantool to view the trouble codes. Or you could simply install the injector. We've had very few problems with that style injector here so if that were going into my vehicle I'd probably clean the exterior and install it as-is.

Thanks for the info and the personal experience. I probably will do as you say: some resistance testing and exterior cleaning.

Originally Posted by tayto

just so you are aware the 7427 will not fire the injectors sequentially. it only will run batch fire and you will have to wire the injectors accordingly. as far as cleaning injectors, i do it all the time now. recently went to the junk yard to get a set of injectors for a civic and then dropped them off to get cleaned. had to go back and get another set (8 injectors total) just to get a good set of 4 FWIW...

EBL is a cool product, but i don't really consider it an upgrade running it in parallel with the 7427. unless you are running forced induction or some other power adder.

Thanks. Yes, I understand that 7427 (and EBL) will only fire the injectors in batch mode. From what I've read, I'm not too concerned about that. As for EBL, agree that having to run a parallel 7427 is a hassle and lowers the value. The benefits as I see it are ability to flash, hi-way mode, higher resolution tables, not having to modify a 7427 for 8 injectors, increased reliability (i.e. less worrying about 30 year old electronics) etc. Still trying to decide if those things are worth the $450.

**tayto** · 05-03-2022

a datalog cable, chip burner and emulator can be had for less than EBL. especially if you are not in a hurry and don't mind picking up a used one. the 7427 can run a semi-open loop mode to run a leaner mixture. there is also some info floating around out there about deleteing the EGR and hijacking it's parameters so you can change the advance in this pseudo hiway mode. it was done 10-15 years ago. As far as "30 year old electronics" EBL only replaces ONE board in the original ECM. The mainboard is still "30+ years old". EBL is modded in a similar fashion to run PFI, so that is a moot point. the only difference is dynamicefi does it for an additional fee. as far as resolution, don't get me wrong EBL is amazing especially when you go and look at the original 747, but the 7427 is still superior. like i said before if you are going forced induction or power adders EBL is the way to go.

https://www.thirdgen.org/forums/diy-...ml#post3651186

LEAN CRUISE:
a. The $0D mask does not have the ability for spark advance during lean cruise.
however, there is a work around if you don't run an EGR valve. I'm going to reveal
another one of my secrets here. This actually works very well. If you don't run an
EGR valve, which I don't, you can leave the qualifiers set to enable EGR, disable
error 32, and set the Desired EGR table and the Fuel Reduction % w/EGR on table to
all zero's. By doing this you will have zero % EGR commanded as well as zero fuel
reduction (remember you are doing this with lean cruise) but the EGR Spark
Correction table will still apply. You can then set this table to add spark where
you are removing fuel with lean cruise.
As for what you should do to tune open loop fuel safely. That is simple, remove
your cat. Here's what I did, I took my old tired original cat and gutted it. I
then bought a cheap universal Catco converter from Summit and fabbed up the pipes
to be able to replace it when it is time to pass the sniff test, then I remove it
after testing. Cost me like $60 total. This accomplishes two things. I am running
a gutted cat for 51 weeks out of the year and when I do install a cat for testing,
it is like new and a new cat can be very forgiving when getting sniffed. HTH

b. enable open loop and the AFR vs VAC vs TEMP table can be used for lean cruise

**Daveo91** · 05-04-2022

Originally Posted by tayto

a datalog cable, chip burner and emulator can be had for less than EBL. especially if you are not in a hurry and don't mind picking up a used one. the 7427 can run a semi-open loop mode to run a leaner mixture. there is also some info floating around out there about deleteing the EGR and hijacking it's parameters so you can change the advance in this pseudo hiway mode. it was done 10-15 years ago. As far as "30 year old electronics" EBL only replaces ONE board in the original ECM. The mainboard is still "30+ years old". EBL is modded in a similar fashion to run PFI, so that is a moot point. the only difference is dynamicefi does it for an additional fee. as far as resolution, don't get me wrong EBL is amazing especially when you go and look at the original 747, but the 7427 is still superior. like i said before if you are going forced induction or power adders EBL is the way to go.

https://www.thirdgen.org/forums/diy-...ml#post3651186

You might be talking me out EBL. I still think there's some benefit, but not sure if it's enough to justify the cost. If it had trans control I think I could much more easily justify. (of course it would cost more then, too). I have cables and chip burners already, been burning chips for years, so that's not a factor, other than the fact that it would be nice to not have to burn chips all the time. Thanks for the TGO link on hiway cruise. I'll check it out in detail. I've read some of the other posts on the subject, but this one is not looking familiar yet.

**Daveo91** · 05-15-2022

I believe I've hit a show stopper with the stock Vortec MPFI conversion project. The thermostat/water inlet housing on the manifold has an interference with the serpentine accessory bracket system. I'm not seeing a way around it - interference is too great to be solved with just grinding off some metal. I think I'm going to abandon the project unless another solution presents itself.

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I'm going to stick with TBI for now. Although disappointing, the disassembly I did today is not a waste - I'm putting in new roller lifters. (When I rebuilt my engine, I used the lifters from the core vortec engine where I got all the rest of the valve train parts to do the roller conversion. I always regretted that decision and I've since taken apart another SBC that had one of those fail - it pretty much made the block useless)

I'm going to consider some aftermarket MPFI conversion systems eventually. For now going back in with my TBI system - it's been running really good after my tune so I'm not super disappointed. I'm going to see if I can get cruise control working this time, too.