Hi guys. I need some help from those 'in the know' for my 91 Caprice wagon. Heres the situation:

replaced anemic, worn out, stock 305 with a 350 4 bolt for a truck, and put on the Edelbrock 3501 TBI to MPFI manifold kit(also designed for a truck). When I called Edelbrock, they said I'd need to swap out my ECM to a 1227747 with a broadcast code ARJU. I went to NAPA and asked for one, but being a reman part running through thier system, the only #'s that match are the 7747 part. Got the vehicle running, but it never really had the power I'd expected, but I figured the new engine was just really tight. Wrong, because it didn't get better. About a week ago, as I pulled onto my road, I could not give the car any gas or it would fall on its face. I idled the last 1/4 mile to my shop, and began to investigate. Went to pull codes, but I had no SES light. As I thought more about it, I couldn't remember EVER have a SES light, even on start up. I pulled the dash face plate to change the bulb and there wasn't one there! Previous owner probably couldn't get it to go off, so apparently I've been driving the car for a couple years with come kind of SES light, but didn't know. Shame on me, I guess.

Anway- I'm wondering if anyone here has had any experience with putting a system like this on thier car. The Edelbrock tech said I may not be able to make it work since its on a car, but unless I'm miising a big piece of this puzzle, I can't see how it would not. He said I may have to have a custom chip burned for it, but again, why?

Thanks in advance for any help/referrals. I need to get this car back on the road and running correctly. Its for the Warden, and the kids all want to "take the purple car", whenever we go somewhere. I've done a ton of work on it, and this is the last piece to make it a done project.

Darryl

 

I guess I should have performed a search before all that typing. Tons of info that starts to be chinese to me after a few responses from the informed. A 7730? Re-pinning it? I have no way to or knowledge of how to burn chips, so that is out. I just need a nice resonably powered wagon that can get out of its own way and get decent mileage. This is a mom's car. Looks cool, not a racecar.

Thanks.

 

I have a 92 Love them long roofs! Anyways, if i were you. I would get a hold of a ADLD cable if you have a lap top. You'll be able to read what the wagons doing. The codes aren't all there is to this. You have a host of sensors that could be acting up as well. So I would start with a ADLD cable to help you see what's going on. The comp program is WinADLD and that is also free

Second, contact Brian at tbichips.com or email him from there. He has a WEALTH of information about set ups and chips such as ours. You cannot believe what a chip will do!!Any setup IMHO needs a fine tuning. No matter how good we think we are. This is also where the cable will come in handy. Brian can "read" whats going on EXACTLY and fine tune it even better for your application.

I am running the same ECM as you as my car came with a 350TBI. I've done headers, FULL 2.5" dual exhaust, pulleys,etc. so if you ever need any help there I can help as well I just bought a GM crate motor and am beginning the process of making my wagon haul the mail Good to see you here. There is a HUGE amount of info on TBI's,etc. here, and some people that are truly blessed in helping us all. Best of luck.

DJ

 

Thanks, I'll email Brian right away. I do not have a laptop, but I did pull the codes via the code reader, and got a low voltage signal from the MAP, and also one from the ESC. The worst one was the dreaded 51 (bad ECM/PROM), which is what caused me to end up here. Looks like I found the right place.

Darryl

 

You may want to do some searching on the merits, and downfalls of mail order chips. The information on how to burn your own chips is right here on thirdgen. Read the stickies at the top of the DIY prom page before you decide you can't do it. I look at mail order chips like sending your carb off to be rejetted based on...well it doesn't run right.

When you made the switch from a '746 to a '747 ecm, did you repin the harness? Some wires go to the same place, but some don't. Look up a wiring schematic for both ecm's. I also thought that edelbrock included a chip with that kit. If they do, you most deffinately need to get ahold of that chip. Running a multi port setup off of a TBI ecm isn't the best idea for a number of reasons, but if your not willing to get into chip tuning it's your only option.

Good luck! and keep asking questions you'll get it figured out.

 

I agree with you. I am not afraid to do the burning, just no real knowedge/equipment yet. I think my Mom just got a new computer, and I'd bet I could have the old one. Got to get into this anyway, since whatever I put my kids in will need proper tuning and maintenance.

I appreciate the support. I am just scrathing the surface of this, and I am aware that I have ALOT to learn!

 

I have figured out the pinout differences between the 746 and 747, but now I'm considering the 730 swap for all its benefits. Is there anyone here who can tell me how to go about putting all this together? I need someone who's already spent the time, made the mistakes, and figured this out. Time is my enemy, and I always seem to lose.

Please help!

Thanks,

Darryl

 

No mention of changing the fuel pump. You need a higher pressure pump, if you still have the original pump in the tank.

 

8746 and 7747 are one and the same hardware wise. Just the code is different. What are the specs on the injectors that edel uses? Not real familiar with them but if their low resistance then its no dice with teh 7730. The later P6 tbi/cpi ecms can easily drive them, though, and they also can support MPFI, but Im not sure what happens on the hardware side when using the interrupt driven injector firings. Worse comes to worse you can just use the standard tbi mode. The big bonus is that theyre true speed density and not garbage density like the TBI ecms and they have more functionality. Theres also the new expantion boards coming out for the stock tbi ecms if you want to use those.

Either way, its likely that no stock cal will work with your motor, regardless of what edelbrock says. Youll have to tune it if you want it to work properly.

 

High impedance, wired in series.

4 injectors are fired instead of 1 TBI injector.

 

IIRC, their all driven off of one driver and hooked in parallel (i think) with the 7730, so if the impedence matches that of standard saturated injectors then theyd work with that ecm.

 

I have replaced the pump with the one called out by Edelbrock. Injectors are 19lb/hr.

According to the schematics I have pulled off of this site, the 'hardware' between the 746 and 747 may be the same, but the pinouts are in different locations on the plug. I can easily swap the wires on the harness, and try the 747 and its chip(the one from Edel) and report back. I'll try that this weekend.

From what I can interpret from reading all the posts that I have, it would be to my advantage to start with the 7730, and try to work it from that starting point. If I was to go that route, what parts/pieces do I need to collect for the car? I understand the laptop, ALDL cable, software, ECM, re-writeable chips, burner, eraser and time. I need the pinout chart for the 7730, to adapt my cars harness. Am I correct to think I'll need plugs for both the 747 and the 7730 to make an adapter? I thought I saw that the plugs are configured differently and won't plug into each other.

Thanks for the responses guys!

Darryl

 

OK, I've got all the hardware to do the 746 to 730 swap, except to keep the re-pinning as easy as possible, I'd like to have an empty set of harness plugs to swap the wires into. What are the part #'s for the 32 and 24 pin plugs? Anyone have 2 32's and 1 24 laying around? PM me if you do. I don't have alot of spare time to search wrecking yards. Wish I did.

Thanks guys.

 

Your stock ECM should be the 6965, not the 8746.

 

Not according to everyone here, as well as all the schematics I've seen.

Thanks, though.

 

kevm14 is correct. And he knows because he owns a 93 Caprice and has programmed his on EPROMs for it. I know because I own a 93 RMW and a 93 Caprice sedan.

The 91-93 cars used the 6965. The earlier Bcar (1990 and earlier) used the 8746 at least with the TBI. Search using 6965 and you'll find confirmation. Here's one post with more details:

https://www.thirdgen.org/techbb2/sho...highlight=6965

 

Yep, I'll verify that too, 8746 was in 89-90 cars, I've searched many cars in junkyards to only be disappointed in finding a 6965 hah. Not sure what the pinout differences are between the two, but I would pretty much guarantee they aren't exactly the same.

 

My original engine was the 305 w/TBI. What tells me which one I had originally? I'll need to have all that info PRIOR to re-pinning! Crap. I thought I had all this ironed out.

 

I bet this confusion stems (and has stemmed) from this information source:

http://www.tunercat.com/tnr_desc/ecm_sup.html#chevycars

Look at the 8746. It shows 89-92 F and Bcars. This is incorrect. I bet someone ASSumed that because the 3rd gen used that ECM in that time frame that an L03 in a Bcar must, as well.

For further proof, look here:

AC Delco

The ECMs are basically identical on a hardware level. They're in the 7747 family, and as such they are ALSO compatible with EBL. I am still unsure if any wiring changes are necessary when installing the EBL in a compatible ECM. I suppose if GM changed the I/O port usage around (ADC input ports, like interchanging IAT with CTS, for example) that some re-pinning would be necessary.

 

So now I need a schematic for my stock ECM, so I can adapt the re-pin to the 7730. Any help? I searched and found nothing.

 

Somebody would have to scan a picture from a factory service manual. I have one but it is in another state.