I remember someone doing this recently, but couldn't find a thread-

there was a '90 in the u-pull-it, so I grabbed the ECU, sensors, and engine part of the wiring harness. It all looked VERY familiar after working on a couple of '89's. My FSM is for an '89, so I haven't compared diagrams yet to see if it's a plug- in swap.

The only real advantage that I saw was that the '90 was reputed to be sequential injection vs. the '89's batch injection. Well, that, and I could block off the EGR, too...

But I opened the ECU (and fixed the leaky caps) and it doesn't look as though there are enough drivers to run the injectors sequentially AND the IAC.

So, 2 questions (finally <img src="/forums/images/graemlins/rolleyes.gif" alt="" />)

1: is it a plug- in swap if I change the engine wiring harness (right side)?

2: is the 90- 91 really sequential?

Thanks,
Toby (stuck at work tonight with an internet connection and little to do...)
<img src="/forums/images/graemlins/drunk.gif" alt="" />

I doubt it, but can't say for sure.


Yes.

Why would you want to do all that work for little, if any, gain <img src="/forums/images/graemlins/confused.gif" alt="" /> ?

kinda went through that when i did my body swap... my ecu from my 90' wouldnt work with the 89' donor chassis. after talking with mistu about it, they ran the 2 vins and i found out one was cali, and the other was federal... but that was only part of the problem. allegedly the wiring harnesses (&ecu) are so different between the 2 years it would require alot more than just simply swapping out part of the harness. youd basically be looking at major wiring issues to deal with... far to many to make it worth it. btw, if you do get it to work... youll have to swap in the dizzy that goes with that ecu, or at least a similar one. to get mine up and going again after the experiment, turns out alls i had to do was to use the ecu & dizzy from the donor... and she fired right up.

Ah,
maybe that was what I was remembering, Grass...

Well, after comparing diagrams, it's close: the '89 ECU has different pinouts, but almost identical functions. And the engine harness SEEMS to reroute those pins to the appropriate places.
You're right, the dizzy IS different.

So now, time to flop the harness out and see if the interconnections to the other harnesses are the same. So far the only concrete difference in the rest of the truck is the power supply for the heated O2 sensor.

As to "Why?"
'Cause it's my sick idea of fun,
'cause the EGR manifold is cracked, and rather hard to find,
'cause the 90-91 was good for a HP or 2, and supposedly got a MPG or 2 more... at least on paper...
'cause, if the harness will plug in, it's a 2 hr job, max!

Will I ever get to it? Hmm... that's a DIFFERENT question!

<img src="/forums/images/graemlins/lol.gif" alt="" />

Toby

Toby -

I've wondered about that swap also (for different reasons) and I'll be extremely interested in what you find. Great idea if it works. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Frank

ok... got me there, i prefer stacking ball bearings <img src="/forums/images/graemlins/lol.gif" alt="" />.

my milage didnt change a bit until i stepped up to 32's and even then the loss is minimal, if i keep my foot out of it.
[/quote]
when i was trying to get mine working originally, i looked into using portions of the 2 existing harnesses... even though the appearance of the harnesses were nearly identical (only difference was the dizzy plug) and every thing pluged in the way it should have, there was just to many internal differences... i would of ended up with a frankenharness. mabey in my case it wasnt the year difference, but mabey it was the cali/federal issue... it turned out to be way more splicing and such than i wanted to do to make it work, an electrician i aint. if you do get this to work... kudos <img src="/forums/images/graemlins/kewl.gif" alt="" />.