Using adj. MAP sensor for bolt on driveability

[brendan]

I am thinking about building an adjustable MAP sensor as per a link I found through diyefi, I think, and using this and my igniton timing to ensure that a stright GM TBI transplant system will function well enough to be driveable on the 258 in the J10.

A few questions:

If I use the ECU to control the spark, does the original distributor position matter? I believe that it does because the ECU is just pulling certain RETARD values out of a few charts and appling them to the timing. So by adjusting the baseline timing of the distributor, I can shift the entire ignition curve up or down, correct?

I have an Autometer A/F ratio gauge in the truck now. I am thinking that between playing with the timing and by adjusting the Map sensor, I can get a stock Chevy fuel/spark curve to fall within the acceptable limits of my engine.


I would like to get this system up and going without having to buy a laptop, build an interface cable, Eprom burner, etc. ahead of time. Eventually this will happen, but It costs money I'd rather spend in the Summer when I have more free dollars.

[Bill usn-1]

MAP

I think you are getting a little over my knowledge base to give a recommendation on that. I'm sure AFI has a base chip already for the motor you are using(258 right) correct me if I'm wrong.

If you download the sample copy of the Tunercat software I think you may be amazed at everywhere the map reading are used. so playing with an adjustable map...to me would be constantly turning the knob for every driving situation. If you have a chip that is close at the start then it will adjust for small errors in the fuel but not timing.
Tell me what kind of a conversion you are planning. what vehicle and what inj are you looking at using.
Right now there is so much to learn about these ECM's that I haven't started looking at add ons yet. (other than a switch for the O2 sensor to force open loop)

[brendan]

My issue is that I wouldn't really trust a stock 258 chip because I have swapped a head onto the 258 from 94 jeep 4.0 High output. My compression is at 9.0 to 9.5:1 and the breathing of the high intake port 4.0 HO head is vastly improved over the stock 258 head. My thinking is that the character of the engine as a whole is more like the chevy 4.3. the 4.3 revs faster and builds power higher in the powerband than the 258, and by putting the 4.0 head (and header) onto my 258 my engine now exhibits similar traits.

I am concerned that the 4.3 winds up faster than the much heavier 258. also, this engine is in a full size truck, and the 4.3 was never used in fullsize trucks in its TBI trim, right? I am figuring that the ignition curves advance faster than my engine can handle. If I can adjust all my fuel curves at once by adjusting the MAP sensor, I will tell the ECU that the engine is under a load,(which it will be-I6 in a fullsize) and this will, I hope, both increase fuel and decrease advance applied to the engine.

[Bill usn-1]

Map

They did use the 4.3 in a truck and the astro van. At least according to the info on GMECM. Engine code was LB4 for 87-91 and LU2 for 90-91 for the truck. Both should be close to the power to weight ratio. I think the biggest concern would be the length of the runners on 1 and 6. But that is an inherent problem on any inline motor. the middle cyl being a little richer than the outside.
I really think with the number of 4.0 J**Ps being converted there is a lot of chips avail for your combo.
Are you planning on starting with the 4.3 system???
It will cost you $5-7 to build a cable from radio shack then borrow a lap top log the data and send it to someone who does chips.
This is of course after you get it up and running with the stock 4.3 chip.
If you can't find the right chip in a junk yard you can go right to GM and buy a replacement for a truck.

[brendan]

Engine code LU2 was for the 4.3 in a full size truck? Not S10?

There are starting to be quite a few 258's (not 4.0 liters) converted, but the head swap is such a night and day difference in flow and compression I worry that the chips for a stock or near stock 258 will not be adequate.

I am planning on starting with the 4.3 system. The 258's air flow requirements are around 350-450 cfm, so a 305/350 system with probably be a little sluggish. A v-8 sized carb on a 258 is always a dog.

I actually don't know anyone who owns a laptop, believe it or not.



let's start from the start:

85 JEEP J10 long bed 4x4
258 I6 with 4.0 liter HO head and header
bored .060 over
crane 260H cam(mild RV grind)
Engine completely balanced (crank spun up to 8000 rpm)
motorcraft 2100 carb
T176/np208 (t176 is a 3.56:1 1st gear four-speed)
3.31 axle gearing
BIG CAP duraspark with TFI coil

[Bill usn-1]

map

The gmecm does not specify other than it's not for the sy/ty.
there is a new prog at tuner cat that list every prom used and it's build date. Just saw it so I'll load it up. the trial only gives 1990 model yr but it's a start.
What's the astro weight compared to the J10?

Keep in mind all sbc(and 4.3) TB's are the same housing, only the inj's are different sizes. so the CFM will be the same. It's all in how much fuel you program into it.

[brendan]

The tip on the cfm is good to know. I assumed the bores were different.

All the astros are auto's right? I thought this might be undesirable. Maybe not, though. I used to drive both an AWD astro and a 2wd astro, both 4.3's, and the AWD drivetrain sucked a ton of power out of the vehicle. Maybe that would be a good starting point. the weight might be comparable. I bet the j10 and scout II are pretty comparable in weight, if that helps.

[brendan]

Bill--

I was able to find alldata recall bulletins on 90 and 91 c1500/2500 2wd/4wd 4.3 v6 trucks. I'm going to make this my target ECU.

According to http://www.cruzers.com/~ludis/idxref.html,
this ECU is the same as basically all chevy trucks from 87-91? or am I missing something?

thanks, Brendan

[Bill usn-1]

ECM

If you are asking about the ecm itself, then yes the box(1227747) is the same. But as TORC soon found out, you can not interchange the chips from a 4-6-8. There are 2 of them under the cover on the ECM. you need both from the same type vehicle.
I would get the whole system from an astro van then just replace the main chip(mempak) with the one you want. provided it is a 7747 ECM in the astro.

[brendan]

Bill wrote "you need both from the same type vehicle."

Do you mean a vehicle with the same number of cylinders?

"I would get the whole system from an astro van then just replace the main chip(mempak) with the one you want"

Why astro, specifically? just because of the weight and 4.3?
By main chip do you mean the eprom or the ROM chip? I had figured that the model # on the ECM corresponded to the ROM chip inside.

[TORC]

The 1227747 has two removable chips. The bigger one is the eprom and the other little removable chip is the Calpak (NetRes). I know part numbers for a Calpak for a 6 or an 8 cylinder, but I don't know of any for a 4 cyl.

[Bill usn-1]

4.3

I would go with the astro just because in all my junk yards looking for systems there is always astro vans there. To find a 4.3 full size in the yard might take awhile. If you really wanted to go with the truck eprom(prom, mempak) then you can look for one or just buy the one you want.
Yes the ECM chips will need to be from a vehicle with the same number of cylinders. I don't think a 6 cyl will run very good on 4 or 8 cyl chips.
The code on the outside of the ECM should corespond with the prom code. ABUL is a 4.3 astro from 1987 in a 1227747 ECM plus, ADWD, AKDX, AKSN, APAB, ATKX...all on the GMECM site.
It doesn't give the exact aplication for each.

So as you scour the yards look for the astro van (or vehicle of choice) with a 1227747 ECM with the code you want or buy the code you want.

I bet TORC has a 4.3 eprom and calpac since he bought an ecm for a 6 cyl and swapped the chips for a V8.

[brendan]

Thanks a lot, Bill! you're really starting to fill in the holes in this mystery for me. I was wondering what all the names on those .bit files represented.

TiminMB(Tim in Manitoba) on the ORC BBS is just now running a Megasquirt system in his CJ using a 305 TBody. He says it runs great. He's using a modified chevy 350 VE table. I'm going to find out about his ignition curves. he's using the modified HEI distruibutor.(Chevy) I'll share what he finds out. Hopefully, some of the scout II Red-Headed step kids can use this info.

two repeat questions:

1. Anyone know what the EVRV solenoid is? I see it on the wiring diagram and haven't come across any online reference to it.

2. Bill, are you using the GM ECU to control spark with the modified Holley/Duraspark distributors? If so( I assume so, considering the 'wire shut the mech. adv. ' step), how does the wiring go? Again, I'd be happy to generate a diagram for your site if you don't have one.


Thanks, everyone. Hopefully your answers to my questions are helping all the lurkers on this board to get a hold on what's happening in the GM system.

[Bill usn-1]

wiring

Brendan:
Yes... I use the ford conversion on all of my TBI conversions.
Mark just completed his GM dist conversion so hopefully I will be able to try it and give everyone another viable option!!!

For the ford dist wiring you will have 3 wires coming out of the dist.(most of them) some only 2 depending on the ground wire.
All the ones I have are 3 and are:
1. Black with orange stripe
2. Black with purple stripe
3. Black

The orange goes to the "N" terminal of the EST
The purple goes to the "P" terminal
and the Black to Ground. That can be straight to gnd or tied to the wire harness ground which is black with white stripe.

I think AFI answered your other question in one of your other post.

HTH

[brendan]

Thanks. The other side I can figure from my wiring diagram and my friends Blazer. Do you mount this in the cab near the ECM? Does the EST need to be grounded?