General Engine Related Talk and Questions

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89Suburban

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1989 GMC Suburban V-1500 1/2 Ton 4x4 350 TBI 700R4 Fuel Pressure Testing

[yt]-AUykhsG3zQ[/yt]
 

89Suburban

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Jim, I am showing 4V at terminal "b". I got lucky this time trying to pull codes. Got 3 strong 12 codes, then what looked like to be a 32 when it started to fade away.
 

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And that would make sense too, why he'd have low vacuum at idle. EGR may need taken out and cleaned up so it can open and close properly. Might even have to clean the intake EGR port up some. Sounds like that low flow might mean a blockage of sorts or heavy carbon build up. Run the bitch lean for a bit and run some ethanol. That might help clean some of that up and allow it to burn off.

I would rather he chuck a pice of bicycle cable into a drill, and use it as a roto rooter....gotta double it over, btw.
It seems to me like he has good flow, because it runs like **** when its hooked up.
Also, Low vacuum would make it run rich, but he mentioned that it backfired through the TB yesterday.

Look guys, in a nut shell, the heads are brand spanking new, all the gaskets are brand new, the EGR is brand new. I don't see how there can be any leaks or clogs. The intake manifold is from a donor truck, I cleaned and checked everything properly regarding the EGR passaages. When I hook that EGR to ported vacuum it almost shuts the engine on accel off idle. That soleniod is not doing it's job. I am getting a 32 EGR system code, well, at least that, the codes die out after the 3rd to 4th rounds of flash. I get a 4V reading off the pin B. That is confusing to me, since it is powring a 12V engine light bulb. Which is another clue, there is not full voltage at pin B, why? Is that normal? These are the questions that need answered, clues. Does the ECM have a bad or low supply of voltage? You wouldn;t think so if you are reading 12V at pin F, and as soon is that is grounded blasting a 10 amp fuse apart.

TCC does not lock up, have power for it at pin F, when grounded to activate the TCC it shorts the fuse. I have no idea why the hell the TCC is tied into the dash guages fuse, wtf is that all about? I do get a 12V reading from pin F, it does disapppear when the brake is applied, as it is supposed to. IMO, if that pin F is grounded, and blows the fuse, that is only because of one thing, something in that line that is supposed to create resistance when activated, is not doing that. There is not a short though, becaus that itself would be either popping a fuse, or burning the ECM up, wouldn't it? Thoughts? If you take a fused, hot wire and touch it to a direct ground, the fuse will blow. If you touch it to say, a light bulb, or a fan motor, etc, that device it is connected to creates enough resistance that it does not blow the fuse.

I got to go look for a diagram how thw TCC soleniod is wired to...

On a side note, I do notice a difference in performance with the new fuel filter. I did not take a pressure reading before replacing it to document any change, if anything, I would say the fuel flow increased, not the pressure. I just ran to the beer dist and back, big long hill coming back home, romped on it and she did a lot better than normal, when I got to the top she kicked into OD, she definately has a little extra oomph. Water temp did jump to 210 in the process though. Don't know if that is normal or not....
 

crazy4offroad

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Backfire through the tbi screams vacuum leak to me. Maybe one end or the other of the intake has a little leak?
 

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Here ya go Bro!
Pin B is not powering anything at all, its just an actuator wire for the test proceedure.
The check engine light has hot power to it when ever the key is on. The ground for the light is operated by the ECM. That samemground wire, branches off to pin D in some trucks....not yours unfortunately.
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89Suburban

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:popcorn:
 

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I am not 100% sure of the square marked IP, but having had the entire harness apart, i assume that denotes the branch off for the diagnostic port. I did inquire about that yesterday to a tuning Jedi on the EFI forums, may hear back today.
The high gear switch:that senses fluid pressure when the 3-4 gear circut is activated, letting the ecm know that the trans gear selector is in OD or D.
When you pull your ECM out to check that pin that I was talking about, we can see if all that shtuff is working too.
 

89Suburban

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I am not 100% sure of the square marked IP, but having had the entire harness apart, i assume that denotes the branch off for the diagnostic port. I did inquire about that yesterday to a tuning Jedi on the EFI forums, may hear back today.
The high gear switch:that senses fluid pressure when the 3-4 gear circut is activated, letting the ecm know that the trans gear selector is in OD or D.
When you pull your ECM out to check that pin that I was talking about, we can see if all that shtuff is working too.

Is it possible that high gear switch is no good?

It's driving me crazy wondering why grounding that pin F is blowing that fuse up. Looking at that diagram it just don't make any sense.

When I yank this ECM out for testing, can I leave it laying on the floor for a while until we figure out wtf is going on? Is there enough slack in the wires to do that?

That "IP" box I am pointing to, we got to figure out what that is. If it was going to the test connector (ALDL) It should be labeled as such, just as it is in the lower part of the diagram for pin F, see that? And also for the fuel pump relay there, it's labeled ALDL "G".

And what this does not show, is the actual ground pin A.

:popcorn:
 

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Is it possible that high gear switch is no good?

It's driving me crazy wondering why grounding that pin F is blowing that fuse up. Looking at that diagram it just don't make any sense.

When I yank this ECM out for testing, can I leave it laying on the floor for a while until we figure out wtf is going on? Is there enough slack in the wires to do that?

That "IP" box I am pointing to, we got to figure out what that is. If it was going to the test connector (ALDL) It should be labeled as such, just as it is in the lower part of the diagram for pin F, see that? And also for the fuel pump relay there, it's labeled ALDL "G".

And what this does not show, is the actual ground pin A.

:popcorn:

*Yes, I have been driving mine around with the ECM hanging out of the glove box hole while tuning with the laptop.

*Yes, agreed, it should at least say "to pin F", but the digrams are from GM for their use. I have suggested modifications to be made for the EFI hobby community.
*didnt notice that, look at G on your ALDL and see if there is a red/ white stripe wire there.
*A is just to a chassis ground. You can also ground B to the ash tray if you want.
 
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89Suburban

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Yah, I was lurking over there and saw your post james, lol. :roflbow:

What you think about the 3-4 switch? :popcorn:
 

Jims86

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Yah, I was lurking over there and saw your post james, lol. :roflbow:

What you think about the 3-4 switch? :popcorn:

We can test that when you pull the ecm out. the switch closes a ground, so, set your meter to scream for continuity, and connect one probe to ground, and the other to the pin that the switch goes to. maybe take it for a drive to see if it yells at you when it shifts into3-4.
Did you ever trim down this torn vac line plugged into the chec valve above the dist?
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89Suburban

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Did you ever trim down this torn vac line plugged into the chec valve above the dist?
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Yah, I took care of that vacuum line, and my CC started to work, lol! :shitsweak:
 

79K10

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sorry to be butting in here, just gonna see if anyone has any input on this.. I think the water pump is oem... I think the water pump is cracked, it seems to be leaking from the side of the lower hose tube, does that sound right? do these things just wear out and start to drip? its pretty rusty

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not sure if you can see the drip or not, its kinda a bad pic, its right above the hose (shot from under the truck)

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