87 GMC Sierra R3500 7.4L TBI vacuum diagram

[Captain J]

Hello
I need your help
I’m looking for the full TBI vacuum diagram for a 1987 GMC Sierra R3500 with 7.4L (454) engine & auto trans. The workshop miss up some vacuum hoses, and I need to put them back correctly
Thanks

[DieselSJ]

There aren't many. I'll try to get a picture of the label on mine.

[Captain J]

Originally Posted by DieselSJ

There aren't many. I'll try to get a picture of the label on mine.

I truly appreciate it
If you like, I can take pictures and post it so you can get better understanding

[Sabaka454]

See image

[Captain J]

Excellent, thank you very much
The AIR system is removed,
there is a 2ed PCV on the second valve cover do you know where the hose go to?
Additionally there is a valve behind the TBI (F port) from the manifold sticking out with its port capped, do you know where if it should be capped or what

[Captain J]

Here are some pictures

[DieselSJ]

Originally Posted by Captain J

Excellent, thank you very much
The AIR system is removed,
there is a 2ed PCV on the second valve cover do you know where the hose go to?
Additionally there is a valve behind the TBI (F port) from the manifold sticking out with its port capped, do you know where if it should be capped or what

PCV valve is in passenger side valve cover. Driver side valve cover should go to base of air cleaner to provide fresh air for PCV - it is just an open connection with no valve. Unless the previous owner of mine reversed it... Basically one side with PCV should go to vacuum source, and other side is fresh air supply.

Fitting sticking up out of the manifold behind TBI provides vacuum to A/C controls and modulator on automatic transmission.

[Captain J]

Originally Posted by DieselSJ

PCV valve is in passenger side valve cover. Driver side valve cover should go to base of air cleaner to provide fresh air for PCV - it is just an open connection with no valve. Unless the previous owner of mine reversed it... Basically one side with PCV should go to vacuum source, and other side is fresh air supply.

Fitting sticking up out of the manifold behind TBI provides vacuum to A/C controls and modulator on automatic transmission.

Much appreciate it,
On regards to the fitting that supplies vacuum to the A/C controls and modulator on automatic transmission, should it be capped or where does go to?
Thanks

[DieselSJ]

Originally Posted by Captain J

Much appreciate it,
On regards to the fitting that supplies vacuum to the A/C controls and modulator on automatic transmission, should it be capped or where does go to?
Thanks

It supplies vacuum to the modulator on the trans and the A/C controls. One port would be capped if you have a manual trans and the other would be capped if you have no AC/Heater controls.

[Captain J]

Originally Posted by DieselSJ

It supplies vacuum to the modulator on the trans and the A/C controls. One port would be capped if you have a manual trans and the other would be capped if you have no AC/Heater controls.

I’ve both, the port for the auto tranx is connected,
the AC port is capped, so where does it go or connect?
Thanks

[Captain J]

Originally Posted by Sabaka454

See image

Do I cap the J port if the AIR Injection control valve is removed? Or leave it open?
Thanks

[DieselSJ]

Originally Posted by Captain J

I’ve both, the port for the auto tranx is connected,
the AC port is capped, so where does it go or connect?
Thanks

There should be a vacuum line coming out of the firewall, just to the passenger side of the distributor. The line comes off the fitting on the manifold to a T and one side of the T connects to the line coming through the firewall, and the other connects to the vacuum reservoir (should be tucked over by the main electrical connector on the firewall).

[DieselSJ]

Originally Posted by Captain J

Do I cap the J port if the AIR Injection control valve is removed? Or leave it open?
Thanks

Cap it.

[Captain J]

Originally Posted by DieselSJ

Cap it.

Done, I also connected the AC line as you mentioned (����),
I’ve replaced all vacuum hoses with new silicone hoses, old ones are brittles,
Thanks to you ��

If the truck runs rich, how do I tune the TBI?
This a video that I made on YouTube on how this truck,
https://youtu.be/WHcGnic6_Yo

[Captain J]

Originally Posted by DieselSJ

There should be a vacuum line coming out of the firewall, just to the passenger side of the distributor. The line comes off the fitting on the manifold to a T and one side of the T connects to the line coming through the firewall, and the other connects to the vacuum reservoir (should be tucked over by the main electrical connector on the firewall).

Done, connected it the skinny hose coming out of fire wall near the AC evap, then to the T on the manifold, the other line from this T goes to the tanx
Thanks

[DieselSJ]

Originally Posted by Captain J

Done, I also connected the AC line as you mentioned (����),
I’ve replaced all vacuum hoses with new silicone hoses, old ones are brittles,
Thanks to you ��

If the truck runs rich, how do I tune the TBI?
This a video that I made on YouTube on how this truck,
https://youtu.be/WHcGnic6_Yo

"Tune" a TBI is done with a programmer and a chip. Rich is typically because of bad (leaking) injectors or bad fuel pressure regulator. Take off air cleaner and run the engine and point a timing light at the bottom of the injectors. You should see a nice even cone shaped spray with no drips.

[DieselSJ]

Watched your video. Find out what is causing the CEL. Put a jumper between the A & B pins on the OBD connector (I use a bent paper clip) and turn the key to the Run position (do not start). Light will flash code 12 - one flash, short delay, then 2 flashes. It will do that 3x, then it will start giving codes in that same format - series of flashes, short delay, series of flashes, then a longer delay. We need to find out what is causing that immediate light to come on.

Meanwhile, change fuel filter. I found out mine was very sensitive to any restriction at all. That seems to have cleared up with upgrading to the EP381 pumps.

1 - change fuel filter
2 - get codes
3 - fix codes
4 - set timing and minimum idle speed

[Captain J]

Originally Posted by DieselSJ

"Tune" a TBI is done with a programmer and a chip. Rich is typically because of bad (leaking) injectors or bad fuel pressure regulator. Take off air cleaner and run the engine and point a timing light at the bottom of the injectors. You should see a nice even cone shaped spray with no drips.

I don’t know a programmer in my country and I don’t have a chip, however
I did the light (LED flash light) and I captured it,
On YouTube
https://youtu.be/b3Uxt8WR5YM

[Captain J]

Originally Posted by DieselSJ

Watched your video. Find out what is causing the CEL. Put a jumper between the A & B pins on the OBD connector (I use a bent paper clip) and turn the key to the Run position (do not start). Light will flash code 12 - one flash, short delay, then 2 flashes. It will do that 3x, then it will start giving codes in that same format - series of flashes, short delay, series of flashes, then a longer delay. We need to find out what is causing that immediate light to come on.

Meanwhile, change fuel filter. I found out mine was very sensitive to any restriction at all. That seems to have cleared up with upgrading to the EP381 pumps.

1 - change fuel filter
2 - get codes
3 - fix codes
4 - set timing and minimum idle speed

—————————
I did that and made a video (on you tube) https://youtu.be/gwxRZxo7S5A
6 months ago I changed the fuel filter, intank fuel pumps and sending units (Spectra), and I installed fuel tanks (in excellent conditions)

[DieselSJ]

Code 24 is speed sensor malfunction. The sensor is built into the speedometer. You should be able to see (or feel) the wires coming off the back of the speedometer and make sure it is plugged in. If sensor is bad, then you have to replace the speedo.

Code 44 is lean. I chased lean codes for a while on mine. I had bad wiring to the O2 sensor, bad fuel pumps, plugged filter.

Watched the video with your injectors and they should not be going on and off like that - you want a continual steady spray. I'd probably start with replacing the electrical connectors on the tops because those look bad. There are also small filters on the injectors themselves. Get a rebuild kit and pull the injectors out of the pods and replace those screens. I can't tell if the injector just isn't firing or if you are getting air in your fuel. Use a stethoscope to listen to the injectors and listen for consistent clicking - if it still clicks when you have no fuel spraying then problem is with supply. If it stops clicking intermittently then you have an injector or wiring issue.

[SCOTI]

Originally Posted by Captain J

I don’t know a programmer in my country and I don’t have a chip, however
I did the light (LED flash light) and I captured it,
On YouTube
https://youtu.be/b3Uxt8WR5YM

These computers don't work like or have the tuning ability of an LS/updated computer. A programmer has to burn a chip based on your combo or if it's stock it needs an original chip, or, you need a program to DIY.

I got mine from TBI Chips aka harristuning.com. My combo is mild so it has worked. I do have surging @ idle but it's not enough of an issue that I have done anything about it.

[Captain J]

Originally Posted by SCOTI

These computers don't work like or have the tuning ability of an LS/updated computer. A programmer has to burn a chip based on your combo or if it's stock it needs an original chip, or, you need a program to DIY.

I got mine from TBI Chips aka harristuning.com. My combo is mild so it has worked. I do have surging @ idle but it's not enough of an issue that I have done anything about it.

I live in a place where most of mechanics & electricians have no experience in classic cars like mine, however I’ve another ECM (not sure if new), can I replace mine with it with no modifications?

[Captain J]

Originally Posted by DieselSJ

Code 24 is speed sensor malfunction. The sensor is built into the speedometer. You should be able to see (or feel) the wires coming off the back of the speedometer and make sure it is plugged in. If sensor is bad, then you have to replace the speedo.

Code 44 is lean. I chased lean codes for a while on mine. I had bad wiring to the O2 sensor, bad fuel pumps, plugged filter.

Watched the video with your injectors and they should not be going on and off like that - you want a continual steady spray. I'd probably start with replacing the electrical connectors on the tops because those look bad. There are also small filters on the injectors themselves. Get a rebuild kit and pull the injectors out of the pods and replace those screens. I can't tell if the injector just isn't firing or if you are getting air in your fuel. Use a stethoscope to listen to the injectors and listen for consistent clicking - if it still clicks when you have no fuel spraying then problem is with supply. If it stops clicking intermittently then you have an injector or wiring issue.

———

For the speedo sensor is it behind the cluster? Do you’ve a picture?

So what I should do to fix Code 44?

I did order the electrical connectors, and I’ve a rebuilt kit, and I’ll work on it.

I’ll check the clicking to verify your diagnostic.
When you say ”if it still clicks when you have no fuel spraying then problem is with supply” what you mean?
Thanks

[Captain J]

Originally Posted by DieselSJ

Code 24 is speed sensor malfunction. The sensor is built into the speedometer. You should be able to see (or feel) the wires coming off the back of the speedometer and make sure it is plugged in. If sensor is bad, then you have to replace the speedo.

Code 44 is lean. I chased lean codes for a while on mine. I had bad wiring to the O2 sensor, bad fuel pumps, plugged filter.

Watched the video with your injectors and they should not be going on and off like that - you want a continual steady spray. I'd probably start with replacing the electrical connectors on the tops because those look bad. There are also small filters on the injectors themselves. Get a rebuild kit and pull the injectors out of the pods and replace those screens. I can't tell if the injector just isn't firing or if you are getting air in your fuel. Use a stethoscope to listen to the injectors and listen for consistent clicking - if it still clicks when you have no fuel spraying then problem is with supply. If it stops clicking intermittently then you have an injector or wiring issue.

Is this the speedo sensor.

[DieselSJ]

Originally Posted by Captain J

Is this the speedo sensor.

That looks like the plug. The sensor itself is built into the speedometer. That harness plug in next to the speedometer cable.