Adding TBI and 4L80e to 74 Argosy motorhome

[bkahler]

Brad,
I do not know how accurate Caldata is. Most likely, there was some parts swapping done to the vehicle to have non-matching numbers.

I'm not so sure parts swapping is the answer. The tag is clearly a GM tag and has the numbers on it that I mentioned. One thing seems to fairly clear, the 8625 was never intended for use with a 4L80e. Did the dealers have the ability to create tags to put on the ECMs?

That does bring up another question. As far as the ECM is concerned do the 4L80e and 4L60e look the same to it?

I think a good plan going forward would be use a '7427 PCM. I also think it would be a good plan to use an original 7.4 Liter Memcal.

That certainly looks to be a more viable approach at this point.

[1project2many]

I've searched for over an hour but I haven't been able to find the information I remember from the early '90s. I believe there was a GM service bulletin or two that I put together to come up with an answer to the pcm number question. As I remember it, there were several part number changes very rapidly involving the three numbers in question... 8625, 6395, and 7427. I cannot remember if they were sequential changes or if two numbers were replaced by the 7427. I would agree with dave that you should have a good pcm on hand. Purchase a good used 7427 and keep it handy just in case. Local yards here sell them for $30 to $40.

Caldata uses the same database that I used for BCCFind. It's GM sourced. The decal on your ecm is OE, just like the tag on the transmission. Service replacement ecm's don't have a BCC on the label. Knowing that there was a short time when part number changed rapidly this doesn't surprise me. I believe this confusion is part of what the bulletin addressed. I believe that your 8625 pcm was used with the 4L80E calibration from GM and it appears to have worked for years. However, just because that controller works with the early variant of the transmission does not guarantee it will work with a newer one or even an old one with updated components.

[buddrow]

With the '8625 PCM the 4L80E transmission would not shift. I tried a spare '7427 PCM, the 4L80E transmission would shift. The really OOD thing is the '8625 would shift my 4L60E.

I think the '8625 was mostly used with the 4L60E in. I think the 16196395 was mostly used the 4L80E. I think the '7427 has some updates to be used with both 4L60E and 4L80E.

dave w

I work very closely with a local salvage yard and from my findings, the 8625 is usually found in 4L60E equipped vehicles. The 6395, 4L80E, and 7427, both, as Dave W has stated. Not a definitive application list as GM did many strange things in those days, but pretty reliable info.

You probably won't notice any issues using just about any year transmission with either pcm. Luckily, unlike Ford, GM didn't change the solenoid resistance every other year(or so it seems) so you won't run into any issues burning out quad drivers and such.

Just my 2 cents.

Buddrow

[bkahler]

Based on Dave w, buddrow and 1project2many's comments it would appear that the 7427 ECM is apparently the better of the bunch. Looks like that's the direction I probably ought to head

I'm assuming it's faster and more reliable or is it something else?

[1project2many]

I'm assuming it's faster and more reliable or is it something else?

Not faster.
Probably not a reliability issue.
Something else is the only option left.

[bkahler]

Where and how is the MAP sensor mounted on a 454 circa 1994?

I need the map sensor bracket and so far I'm not sure what I'm looking for.

This map sensor bracket is listed for the small blocks, would it work for a big block?


Thanks!

Brad

[myburb]

The bracket mounts on the pass side just forward of the rear by a couple intake bolts. The proper intake bolts have studs on the top to mount to. Being as it mounts to intake bolts I would think the spacing is big block only.

[bkahler]

So I'm looking for a bracket AND a couple of mounting studs.

Thanks!

[buddrow]

Make sure the vacuum line is short as possible and does not dip or have loops or anything of the sort as fuel may collect in the vacuum line and cause erroneous MAP readings. FYI.

Buddrow

[Six_Shooter]

You don't need a specific bracket for the MAP sensor. You can mount it on the firewall, the side of the air cleaner, etc, then just run a vacuum line to it.

Keeping the line short is good, but it doesn't HAVE to be. I've mounted the MAP sensors inside with a long (but hard) hose and not had any issues.

[myburb]

I only answered the question on the stock bracket. I used them cause I had them and found it was a convenient place to mount fpr on the back side. If I didn't have the bracket I would probably look at the firewall or what ever worked good. If you go too far you will have to modify the harness.

[bkahler]

Thanks for the info and tips. Since this is going in a motorhome there really isn't a firewall at the back of the motor so using a factory bracket might be the easiest approach. due to the lack of firewall. Also I'll be running the engine on a test stand first so the factory bracket makes even more sense.

Thanks!

Brad

[dave w]

Might be a good plan to locate a used 454 TBI Ignition Coil with bracket, so you have factory bracket to mount a New Ignition Coil to.

dave w

[bkahler]

Might be a good plan to locate a used 454 TBI Ignition Coil with bracket, so you have factory bracket to mount a New Ignition Coil to.

dave w

Dave I picked up this coil bracket a little earlier today, hopefully it's the right one!

Attachment 10147

As far as bracketry goes I think I'm only lacking two things, the MAP sensor bracket and something to mount the ECM to.

By biggest problem is there aren't a lot of salvage yards close by that have anything worth looking into. Unfortunately ebay is my best source for bits like this.

Brad

[dave w]

That looks like a 454 coil bracket to me. Not sure what years that style was used. I think it will work for you with the Edelbrock intake you have.

dave w