Any TBI experts out there? (New Body Style)

[Dr_Snooz]

I just finished rebuilding the 454 in my '90 C3500. Bone stock rebuild. Everything is back together and the truck runs great at idle and low throttle. At moderate throttle and above, however, it bogs down and loses power. Before the rebuild, the truck had great low end power. When climbing hills with the trailer, the torque at the lower RPMs was awesome. Now, I have to flog it up the hills and it bogs and stumbles the whole way.

The new engine is not 1,000 miles old yet. I replaced plugs, wires, cap and rotor 5,000 miles ago, so they are fairly new. I was careful to mark every plug on the harness, and am pretty sure everything got hooked up as it should, though some connectors got mashed and pulled in all the fun. I don't have a CEL. Also, there is a spare connector sticking out of the harness that I don't remember. It doesn't go to anything I know of and wasn't marked. I don't know where it came from. (?) I set timing at 4 deg. BTDC but after tightening the dizzie down, it moved itself to 6 deg. Whatever.

Anyway, does anyone have any ideas for me here? I want my old truck back.

Also, is there any reason I'm not able to start new topics in the Technical section?

[VileZambonie]

You set the EST in bypass when setting the timing right?

You checked your fuel lines/hoses for kinks?

You can not start a thread in tech pages as those pages are read only. If you have a submission you want to make just create the post and we can move it in there if it belongs.

[Irish_Alley]

I don't have a CEL.

Does your cel light come on when you first turn the key to "acc"

Also, there is a spare connector sticking out of the harness that I don't remember. It doesn't go to anything I know of and wasn't marked. I don't know where it came from.

Picture

[Dr_Snooz]

You set the EST in bypass when setting the timing right?

I didn't! Doh! That's what I get for not reading the manual. In my defense, I did try but didn't find anything in my manual's index for "Timing." Turns out, it's under "Ignition timing."

Obviously, I'm going to fix this, but do you think that would cause my issues?

You checked your fuel lines/hoses for kinks?

They are hard lines that go directly into the throttle body with flare connections. There are rubber lines going from the frame rail to around the trans and they appear to be fine, though a little oily.

You can not start a thread in tech pages as those pages are read only. If you have a submission you want to make just create the post and we can move it in there if it belongs.

Okay. I wasn't sure if there was a problem on my end or not.

Does your cel light come on when you first turn the key to "acc"

As I understand it, "acc" is when you turn the key backward one notch. There is no CEL in that case. Only the radio comes on. When I turn the key forward to "run" when all the gauges turn on, the CEL blinks one time, then holds steady until I start.

Picture

Here's the connector, down behind the distributor.


And a slightly better pic.


Thank you gentlemen so much.

[VileZambonie]

Is your Truck a C3500 or an R3500?

[Dr_Snooz]

As far as I know it's a C3500. The VIN is 2GCGC... I don't know the difference between C and R though.

I have two electrical connectors on my dizzy. One goes into the engine loom on the firewall, and the other goes to the coil. I unplug both of those, correct?

[Da67goatman]

Whats your fuel pressure?  you could have a broken regulator spring.

[VileZambonie]

As far as I know it's a C3500. The VIN is 2GCGC... I don't know the difference between C and R though.

I have two electrical connectors on my dizzy. One goes into the engine loom on the firewall, and the other goes to the coil. I unplug both of those, correct?

So this is a new body style truck.

[Dr_Snooz]

So this is a new body style truck. [/quote]

Correct.

[Irish_Alley]

I don't have a CEL.

Does your cel light come on when you first turn the key to "acc"

sorry that should be "on"

rookie mistake 

[roundhouse]

As far as I know it's a C3500. The VIN is 2GCGC... I don't know the difference between C and R though.

I have two electrical connectors on my dizzy. One goes into the engine loom on the firewall, and the other goes to the coil. I unplug both of those, correct?

No

There is a connector with a single wire

THe wire you need unplug  not come directly from the dizzy
It may be in the harness  Near the dizzy


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[VileZambonie]

So this is a new body style truck.

Correct.
[/quote]

OK so wrong forum and to avoid confusion this is being moved to General Discussion since it doesn't apply to this vintage.

[VileZambonie]

See attached

[Dr_Snooz]

I checked the timing yesterday and it was off by a wide margin. The mark wasn't even visible. I think it was retarded. I kept looking in my books and on the web for directions for setting the timing. Turns out they were on my air cleaner the whole time. Duh. I set the timing properly and the truck is transformed. I haven't yet tried pulling the trailer, but I think it will be just fine. I have a ~15% grade hill here (2nd gear ascent and 1st gear descent) that I use as my proving grounds.

Thanks VZ for the diagrams. Those are very helpful. I don't find that connector on them and there isn't anything nearby that it will reach so I'm not going to worry about it.

[Irish_Alley]

a/c sensor?