carb to tbi conversion

[dyeager535]

Astro vans USED to be a good source for DRACS. They at least used to be way easier to find than trucks. On those, believe the DRACs were located at the top of the dash, center, maybe behind the AC vent? I recall accessing them from up top, and rather easily.

To me since you have the aftermarket speedometer, going with the DRAC setup as suggested by Anwat is likely the easiest. The only other easy/common way to do it is to use the 1983-1989 speedometer cluster setup, but I'm guessing you'd rather keep the speedometer you already have. So yes, GM C/K (R/V) trucks were setup the same as the Astro you had, up to 1989.

 

[Dan Brown]

Okay, thx for the info.

 

[Dan Brown]

Will I need an ESC, or will the ECM take care of advancing and retarding the timing?

 

[anwat]

It will help a lot, especially with the pinouts for the ECM.
As for the ESC, yes, you're going to need it, but that's more the name for the system that controls the spark. What you'll need is the distributor that goes with the ECM. There are several that will work, depending on your budget, I would suggest going with a new one. Nothing is more frustrating than trying to figure out what's wrong when your gear on the distributor is worn or misaligned and nothing seems to work right. Rock Auto is great for part numbers, they will become your friend. You will also need an ignition module to go in the distributor, that's what actually controls the spark. There are several inputs to the ECM that also add into the system, the knock sensor being the most obvious. The narrow band 02 sensor is also important, it tells the ecm how efficiently the engine is burning all the fuel it gets.
If you're trying to set this up like intended, you're going to need the whole gamut of sensors that come on the TBI trucks, they all work together to keep it running. Without one, it's not going to be right. It'll run, but not well. If you're buying an o2 sensor, I'd recommend getting a three wire, heated sensor, otherwise, just get one when yours quits. Make sure you put a disconnect into the wiring on the ESC so that you can set the timing without too much trouble. You need to disable the ESC to set the timing.
For reference, here's a good distributor that will work if you have a roller cam: ACDELCO 19179575, if you have a flat tappet, I'd go with Davis Unified 12620BK.

 

[Dan Brown]

Why and how does the distributor have to go with the ECM. Does it really know what EMC it's getting its signal from? Too, I was told by Larry's Electric that by using the 1227747 ECM that I needed to use a Delco 213-92 Knock Sensor. I thought a Knock Sensor was a Knock Sensor. Whose Knock Sensor did you use? I'm using a TBI distributor that, I think, I got off the same truck I got the TBI unit off of. No roller cam, Competition Cams hydraulic lifter cam. Will find an ESC at the junk yard. Is there a procedure for checking the ESC to determine if it's good? Maybe Youtube has a video on checking it. Found a new one on Amazon but it seemed a bit pricy.

I, too, use Rock Auto and will check their prices for some of these items.

Thx, Anwat.

 

[dyeager535]

Knock sensor is particular to the displacement of the engine. That ECM was used with multiple displacements, so at best you could say the PROM is matched to the knock sensor, but that overly complicates the matter.

Acdelco.com 's part number cross and search is pretty decent for this sort of thing, as is rockauto. You can also download the parts manual from the previously given website and start from the gm part number. I usually start in the parts manual if there is any question, as the proper vintage parts manual is IMO more likely to be correct than other, newer sources.

 

[anwat]

I'm assuming you know what year the donor truck was for the Throttle Body and ECM. My suggestion would be to just pretend you engine is now that year. When you look for part numbers, look for that year k5 with a 350, and buy all your parts to match that. As far as the distributor goes, yes, if it came from the same truck/car that you got the other stuff off of, it should be good. The ignition module is actually under the cap so you should be good to go. no need to buy another, check the contact points to make sure they are clean and not worn, make sure there's plenty of heat sink grease between the module and the distributor, and I'd say it's ready to put in. There is a way to bench test your ignition module, I've read a thread here about it. If you search for it, I'm sure it will will pop up. Issue is, some don't fail until they start to heat up, so the bench test isn't proof of anything, really, unless it's bad from the beginning. I say throw that distributor in, hook it up and check for a spark, then go from there. Those ignition components worked together on the vehicle they came from, they should be OK on the new one, too.

 

[Dan Brown]

The first ECM I put on, the 16977427 I know was from a 1995 pickup. I have no idea what the 1227747 I bought from EBAY came off of. As for the distributor, I've already changed the module and greased it up good before installation. Fixing to head for the junk yard to find an ESC and will bench test it and hopefully it will be good. If not, I found a new one on EBAY for 50 bucks, so I could go that way. If all the parts are the same, i. e., distributor, ESC, etc., as that came off a certain truck, shouldn't they all work together even thought not coming off the same truck?

 

[dyeager535]

I believe all the TBI distributors were the same, but at some point they went from coil in cap to remote coil. No big deal there.

Pretty much everything for the same displacement engine is the same. Obviously some sensors cross between displacement, but as we know, knock sensor doesn't, injectors don't, and the TPS doesn't if from a big block.

Should be a sticker on the ECM with three or four letter code on it (ie APYP). If not, open the little cover that has the two screws holding it shut, and get the four letter code directly from the PROM (the chip that holds the programming specific to the vehicle it came in...platform, engine, trans, etc.) Really should verify anyways, people were prone to putting a hypertech chip in as a replacement, and they are garbage. PROM codes can usually be googled, there aren't many one-offs on them, as by that time there was no "special order" going on. Every vehicle package offered was EPA certified, and thus GM kept the number of variations pretty small. Still a fair number of specific PROMS.

 

[bp71k5]

If the VSS has two white wires, it doesn’t matter which one you use for ground. Just ground one and run the other to the ECM/Speedo/DRAC.

I have an autometer electric Speedo that has a VSS output. So I ran my vss on the transfer case directly to the Speedo and then ran a wire from the Speedo output to the ECM to provide VSS signal. Has worked fine.

 

[anwat]

OK, now I'm confused....you keep referring to the ESC. The spark advance is controlled by the module and the ECM programming. On my truck, there is no "ESC", that is the term used for the system of components that control the spark adavance. There is no ESC box or item that can be picked up and changed....some people call the ignition module the ESC module, but other than that, I am confused by what you are going to get at the junkyard. Coil, cap, stator, pickup, module, ECM, wires, and plugs...I think that's about it for the electrical end of the ignition. The ignition module controls the injector pulse as well as the spark generation, but the actual spark advance is controlled from the ECM.
And yes, that was my point in picking a year...although dyeager has a more technical (and probably accurate) way of doing the same thing with the PROM code. Everything off the same year of truck with the same component package will work. Many of the sensors are used over several engines and several models/years. But if they all worked on the same truck to start with, then they will all work together on the yours. I never knew what the 4 letter code was, I just knew to match it. Now I do, and it makes sense why when I tried a ASDW broadcast code it worked even though I was supposed to have an ASDU coded chip. I'm sure there's a list somewhere of what all the codes represent. I'm sure some chips will work across several ECMs, but you're going to lose something somewhere if you don't have the right code.

 

[bp71k5]

OK, now I'm confused....you keep referring to the ESC. The spark advance is controlled by the module and the ECM programming. On my truck, there is no "ESC", that is the term used for the system of components that control the spark adavance. There is no ESC box or item that can be picked up and changed....some people call the ignition module the ESC module, but other than that, I am confused by what you are going to get at the junkyard. Coil, cap, stator, pickup, module, ECM, wires, and plugs...I think that's about it for the electrical end of the ignition. The ignition module controls the injector pulse as well as the spark generation, but the actual spark advance is controlled from the ECM.
And yes, that was my point in picking a year...although dyeager has a more technical (and probably accurate) way of doing the same thing with the PROM code. Everything off the same year of truck with the same component package will work. Many of the sensors are used over several engines and several models/years. But if they all worked on the same truck to start with, then they will all work together on the yours. I never knew what the 4 letter code was, I just knew to match it. Now I do, and it makes sense why when I tried a ASDW broadcast code it worked even though I was supposed to have an ASDU coded chip. I'm sure there's a list somewhere of what all the codes represent. I'm sure some chips will work across several ECMs, but you're going to lose something somewhere if you don't have the right code.

separate ESC came with lots of 7747 computers. I think some big blocks with the computer may not have used them since they didn’t use knock sensors. Really, the OP should get everything from the same year truck ideally with the same trans and motor size.

 

[Dan Brown]

I went to my junk yard today looking for an ESC. Found 3 trucks out of 10 or 12, all TBI and year model not known, that at one time had an ESC of which 2 had already been taken and several never had one as the connector wasn't even there. I bought the 1 off the truck that still had it. Not one of the trucks was a big block. Can somebody explain to me what difference it makes whether the components all come off the same truck. What happens during the trucks live while still on the road and one of the components fails and has to be replaced. The new one certainly wasn't on the truck with all the other components when the truck was new. Also, do I really need a Delco 213-92 Knock Sensor with the 1227747 ECM as I was told by Larry's Electric? Isn't a Knock Sensor as Knock Sensor?

 

[bp71k5]

I went to my junk yard today looking for an ESC. Found 3 trucks out of 10 or 12, all TBI and year model not known, that at one time had an ESC of which 2 had already been taken and several never had one as the connector wasn't even there. I bought the 1 off the truck that still had it. Not one of the trucks was a big block. Can somebody explain to me what difference it makes whether the components all come off the same truck. What happens during the trucks live while still on the road and one of the components fails and has to be replaced. The new one certainly wasn't on the truck with all the other components when the truck was new. Also, do I really need a Delco 213-92 Knock Sensor with the 1227747 ECM as I was told by Larry's Electric? Isn't a Knock Sensor as Knock Sensor?

The components don’t all HAVE to come off the same truck, but it makes it easier to source. If one truck in the yard has all the parts you need, why use parts from more than one truck? The need to be from the same year range that has whatever components your trying to use.

Might also be simpler to just go to the parts store and get a new ESC module?

knock sensors are different. Don’t know what you need but there’s differences.

 

[Dan Brown]

Found a new ESC on EBAY for 50 bucks, paid 14 bucks plus my veterans discount at the bone yard. To me, no brainer. Now the 64 thousand dollar question, how can I test my much cheaper ESC to be sure it's good? Will buy a Delco 213-92 Knock Sensor from Amazon.

 

[dyeager535]

Test procedures (if GM had any) are either going to be in the service manual, or emissions manual if one was used for that year. Usually found under the trouble code for that issue.

 

[anwat]

AutoZone used to test ESC modules for free...don't know if they still do, but I'd start there. If it's bad, you'll show a code 43 once you get it running, but I think you want to check it before then.

separate ESC came with lots of 7747 computers. I think some big blocks with the computer may not have used them since they didn’t use knock sensors. Really, the OP should get everything from the same year truck ideally with the same trans and motor size.

So there's a ignition module in the distributor and a different module called the ESC? In mine, which is a 1990 350 and a 7747 computer, I just have the ignition module in the cap, which is wired to the computer and the coil. Maybe I'm missing a part? I don't have anything that looks like the ESC in this photo:

I just have the module...unless maybe they combined the two at some point? Did all of the 7747 computers use an ESC module, or only some? Just trying to figure out if I left something out when I put mine together...I don't have any codes or lights on, but maybe I should have one one these modules? If I have one where is it physically located?

 

[dyeager535]

I'm confused myself. I didn't think ESC was separate on the truck TBI setups. But yes...some GM applications used an "external" ESC and some did not. But I only know that to be true of the TPI motors ( '85-92, so similar vintage, but not identical to other applications). Started with an external ESC and then switched to onboard (the ECM) the last couple years.

What do the wiring diagrams for the 350 TBIs in say, '87 show? As I recall the ESC, when used, is where the knock sensor wire goes. If the single knock sensor wire goes to the ECM, it shouldn't have a separate module.

 

[bp71k5]

I'm confused myself. I didn't think ESC was separate on the truck TBI setups. But yes...some GM applications used an "external" ESC and some did not. But I only know that to be true of the TPI motors ( '85-92, so similar vintage, but not identical to other applications). Started with an external ESC and then switched to onboard (the ECM) the last couple years.

What do the wiring diagrams for the 350 TBIs in say, '87 show? As I recall the ESC, when used, is where the knock sensor wire goes. If the single knock sensor wire goes to the ECM, it shouldn't have a separate module.

I have a separate ESC module like that and I think my computer came from an 87 or 89 blazer with a 350. But the block is a 454 which came from an era of not using a knock sensor. I was able to do whatever changes I need in the chip. Though it’d be nice to have a more modern wideband O2 system like the edelbrock or FAST, etc but it seems to be working pretty reliably for the past few years so I’m leaving it alone.

 

[dyeager535]

I have a separate ESC module like that and I think my computer came from an 87 or 89 blazer with a 350. But the block is a 454 which came from an era of not using a knock sensor. I was able to do whatever changes I need in the chip. Though it’d be nice to have a more modern wideband O2 system like the edelbrock or FAST, etc but it seems to be working pretty reliably for the past few years so I’m leaving it alone.

Ok, I found reference to a separate ESC module on another old thread on here, but the OP never came back to verify what they were talking about, as there was reference to it being mounted near the master cylinder, and someone asked to make sure it wasn't part of the ABS, and there was no answer.

People seem to confuse the ESC with other stuff anyways, and GM didn't make it easy with the 305's that had a standalone ESC computer pre-TBI either, but if people say they existed on the trucks, I'll believe it. Should be pretty easy to figure out for oneself anyway, it's a pretty unique connector on the wiring harness.