TBI 400 Small Block

[Xenon]

Ok, a little backstory and then questions that will no doubt demonstrate my ignorance.

Got this 'burb in '09. Had a burnt up 5.7l (worst seized engine I ever saw, ran with no water in the radiator)

I got a 400 to put in and decided it'd be neat to go EFI. Put all the tbi components on the 400 exactly as they came off the 350, not quite knowing what I was doing. It ran rather well, had a dead spot off idle and never quite felt like it was putting out as much power as it could until above 3000 RPM. got 10-12 MPG highway, which I thought was stellar for a 7500 lb truck with 4.10 gears. I attributed the less than perfect performance to the fact that it had the stock 400 cam designed for a carbureted engine, something I had overlooked when I put it together.

Somewhere around Feb. 2010 the truck flat died going down the road. I immediately suspected the ECM, as I had been experiencing rough idle, severe surging (45mph to 65mph and back without moving the accelerator) and excessive fuel consumption (5mpg)

The ECM1 fuse was blown. There was no fuel coming from the injectors. It had spark though, it would kinda cough to life if you sprayed alot of ether in it.

Replaced the fuse. Nothing. It did not blow again though, which ruled out a shorted wire in my mind. (EDIT: In my thinking, it ruled out a shorted wire. It in no way ruled out a shorted wire in my mind...)

I was very short on money at the time, I was in Arizona and trying to save up to come to ND for work... So I took a weekend and put a Holley on it with the carb'd manifold that had come on it.

It's never been the same without TBI. doesn't have the power it used to, gets 7mpg uphill, downhill, headwind or tailwind.

I have the time (and some money) to put into it now, as well as a '98 Suburban to drive daily, making this somewhat of a project truck now.

I am here, of course because I want to put TBI back on it, but I want to do it right.

I have the original TBI components off of it, and the TBI components off of a near identical '88 K20 Suburban that I scrapped out for a guy a few months ago.

I have 2 1227747 ECMs, one that I believe to be bad (the '87) and one that I assume to be good, but don't actually know.

the '87's ECM has an AFCB prom and the '88's ECM has a ADYR prom.

My basic idea was to put a 1987 5.7l cam in and put the ECM from the '88 in and plug it all back in.


Please point out all the flaws in this idea and offer your better ideas.

[93V8S10]

Sounds like you've get a plan, just need to get it all back together, so you can work on diagnosing the original problem. Don't worry about the stock 400 cam, it will be just fine, as evident by how well it ran with stock tune.

[EagleMark]

Sounds like you've get a plan, just need to get it all back together, so you can work on diagnosing the original problem. Don't worry about the stock 400 cam, it will be just fine, as evident by how well it ran with stock tune.

Agreed!

Your origanal issue, since you had spark but ran with ether was a fuel problem. So could be faulty relay, plugged fuel filter faulty ful pump?

You ran good on a stock 5.7L chip on a 400 engine is probably why you ran out of power at higher RPM.

Rough idle, surging and poor fuel milage could all be tied together to a vacuum leak.

If you put it all back together we can diagnose what went wrong, fix it, then move you on to tuning the chip for a differant motor.

I don't see any flaws in your plan. Just have to pay attention to detail like vacuum leaks when you do the intake change and TBI install. Rest is pretty simple plug and play.

[Xenon]

Great!!! I was thinking I'd have to go with the stock TBI cam... this, then, is not necesary?

What do you think about the ECM1 fuse blowing? I'm pretty excited about getting this this TBI'd again. Part of the reason I stopped driving it and got the '98 was the poor fuel economy with the carburetor... Also, it's a 4x4 and the '98 isn't, and being in ND the 4x4 is much needed in the winter. Except for this winter...

I'm almost done with the bodywork... fixed the rust and am going to paint it when the weather turns good.

Also just completing an axle swap from the 4.10s to 3.73s...

[gregs78cam]

When you get ready to put a 4L80E in, I have some ideas and tips for you, and if i can find the website, a guy talks about how he adapted the TH400->NP205 adapter plate to work on the 4L80E. But I concur.....get that beast back together, and let go from there.

[Xenon]

Great... It's all about MPGs for me right now, as the 400sbc is more than enough power for daily driving and occasional trailer towing without much extra help... So the 4L80E swap is high on my list once I get it figured out and gather all the parts...

[EagleMark]

Your cam ran good before so it's a good EFI cam. The tune for more cubic inch will help. I wouldn't change a cam for your reasoning...

Suburbans have plenty of room for bigger tires! Stay skinny and go taller and you'll have same overall ratio change instead of changing gears. Tires will be cheaper and WAY easier!