1988 5.7 to 1995 7.4 swap question

[ARCTICboy]

Hey, Thanks for all the help everyone! Are these photos ok?

Marcus

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[Vbb199]

Yea that's a 454 tbi, at least by the IAC valve and lack of provisions for a TV cable.

So that's good. ^


Do you own a vacuum gauge ?

If so, see what kinda vacuum it's making at idle.


And how about that timing bypass plug ?

 

[ARCTICboy]

Hi Vince.
The truck is at my friends shop and they have a vacuum gauge. Will check tomorrow.
Do you have a photo of what the bypass plug should look like?
Also, I found a number on the side of the computer behind the glovebox but part of it is coverd with a bracket. I will get the number as well if that helps anything.

 

[Vbb199]

Hi Vince.
The truck is at my friends shop and they have a vacuum gauge. Will check tomorrow.
Do you have a photo of what the bypass plug should look like?
Also, I found a number on the side of the computer behind the glovebox but part of it is coverd with a bracket. I will get the number as well if that helps anything.

It's a single/1 wire brown plug, as I say it should be near the brake booster. I can take a pic a photo a little later if you'd like.

 

[ARCTICboy]

Hi Vince.

Found the wire, it was connected and it was disconnected when the timing was done, then reconnected. It has good vacuum as well with no leaks.
I was really hoping that was it!

 

[Vbb199]

Hi Vince.

Found the wire, it was connected and it was disconnected when the timing was done, then reconnected. It has good vacuum as well with no leaks.
I was really hoping that was it!

Hm OK, well damn.


You said it idles rough, and bogs under any sort of engine load, but will maintain highway speeds.


The exhaust by chance doesn't smell absolutely pig rich does it? Is the oil stinky with gas?

And that ECM.... I assume you know where it is. It lies behind the glovebox.



I would assume since the OP has the IAC and tps wired up, presumably they did a harness swap as well? I dunno.
So far it's looking all good. The ECM I cannot say for sure how to identify it, but see if any of those numbers maybe match up to something? I have a spare ECM, I know it's a 350 ecm, but I'm wondering myself how to identify that.



Whats the fuel pressure measure? You said you had good pressure, but never specified what it was on your gauge.

The bogging at any sort of load sounds like to me it's overfueling since we've checked off all the basics


Is the injectors spraying a nice, CLEAN upside-down cone shape when it idles?

When I say I clean, I mean you can't see any weird streams or the gas is spraying heavier on 1 side or the other.

You can remove the extension that's for recirculating crank case gasses, and see them with a flashlight.

 

[ARCTICboy]

Hi Vince.

I did some cross parts checking and have to do some more snooping through the truck to see what they did with the swap. So far the ECM is totally different between years, Fuel pump if original is only 12psi and 30psi is required, the fuel sending unit and the TPS are both different as well. Will report back once I get through this list.

Thanks everyone for the help.
Marcus

 

[RecklessWOT]

Also, an R2500 would be a 2wd GMC Suburban. At some point in the 90's, they all became 1500/2500, but for almost all squarebodies, the 10/20/30 will be for chevrolet and 15/25/35 will be for early GMC with 1500/2500/3500 being later 80's GMC

'87 was the only year they retained the 10/20/30 scheme but switched to R/V, 88+ was still R/V but they adopted 1500/2500, once they got that cheap looking black plastic side moulding instead of chrome it had 1500 printed in it like the GMT400 trucks did too.

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look at the driver's door trim