Bad running after manual swap

[JPVortex]

Hello y’all, just recently finished swapping in a 5lm60 to my 94 k1500 with a 350 tbi. It runs great off idle, but at idle it runs horribly.

It’s surging like hell and can’t find where it wants to sit.

fuel pressure should be fine, I just tested it about a month ago while throwing in a new fuel filter. Also rebuilt the TBI unit like 4 months ago.

Coolant temp sensor was recently replaced aswell. New plugs, plug wires, cap rotor etc.

Swapped in a spare IAC I had, actually ran worse on that.

Other than that my next step is probably a smoke machine to see vacuum leaks, it sounds like a vacuum leak to me.

Video of issue:

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Thanks!

 

[JPVortex]

So I have totally thrown the parts canon at it this afternoon.

I replaced the PCV Valve, IAC, MAP sensor, cap & rotor. No difference at all, actually a new development:

The tach seems to be fluttering/jumping now, where as before it was accurate in going up and down with the surging idle.

I'm leaning towards ICM or ignition coil going out. When I put the new trans in the back of the engine smacked the firewall and did break some of the plastic on the ICM by the 2 wire connector, so I'm wondering if I jostled something loose in it and damaged it.

 

[RShrimp]

I have found the easiest way to test for vacuum leaks is a torch. You dont light it, just let is flow gas. If the engine picks it up it will rev. Carb cleaner works too but it makes a mess. Generally if it worked before it is something you messed with and not some random new issue. You may well be on the right track with stuff you bounced off the firewall

 

[JPVortex]

I have found the easiest way to test for vacuum leaks is a torch. You dont light it, just let is flow gas. If the engine picks it up it will rev. Carb cleaner works too but it makes a mess. Generally if it worked before it is something you messed with and not some random new issue. You may well be on the right track with stuff you bounced off the firewall

Yeah I sprayed brake clean all over all the sources of vacuum, rpm’s didn’t change at all at any spot, unfortunately I don’t have a torch to use.

Yeah I’m skeptical of the ICM and possibly even the pickup coil if it got jarred enough. I took a gamble and placed an order on Amazon for a Chinese distributor assembly with ICM and all that had good reviews.

If that doesn’t work I think I’m going to invest in a smoke machine to find a possible vacuum leak, although I am straying away from that now because it ran completely fine before the manual swap, and still does off of idle.

 

[JPVortex]

What’s also weird is here and there it’ll idle perfectly but then I’ll shut it down and start it, then it starts idling bad again

 

[JPVortex]

So update here, did a fuel pressure test and this is the result in the video below. Seems low to me. The pump is not even a year old, so I'm a bit annoyed.

I tested the fuel pressure a couple months back and it was like 12psi(at the filter though) so it has dropped significantly fairly recently.

I tested the pressure at the line going into the TBI unit this time.

Is there anything else besides the pump that would cause the low pressure? The filter is only a month old, the TBI unit is rebuilt about 3-4 months ago, with a new regulator diaphragm.

Heres the video right here:

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[Schurkey]

1. Is the gauge accurate?
2. I'm not fond of using a low-budget, 100 psi gauge when testing for <15 psi. I'm not real fond of using a GOOD 100 psi gauge when testing for <15 psi.
3. You replaced the regulator diaphragm. Did you replace the spring, too? It's the spring that sets the pressure.
4. Was the computer tuned to accept the manual transmission--no shift solenoids, no TCC, etc?
5. Do you have a clutch safety switch?

 

[fancyTBI]

You need a computer and prom for a manual truck of the same year.

 

[JPVortex]

1. Is the gauge accurate?
2. I'm not fond of using a low-budget, 100 psi gauge when testing for <15 psi. I'm not real fond of using a GOOD 100 psi gauge when testing for <15 psi.
3. You replaced the regulator diaphragm. Did you replace the spring, too? It's the spring that sets the pressure.
4. Was the computer tuned to accept the manual transmission--no shift solenoids, no TCC, etc?
5. Do you have a clutch safety switch?

I did not replace the spring for the regulator, but it looked to be in fantastic shape still, i dont think that's an issue. I do agree with the gauge, not a fan of it.

I did NOT make any computer changes to it, am still running the same computer as before the swap. It is throwing codes for an automatic transmission. Wonder if thats the big issue here.

 

[JPVortex]

You need a computer and prom for a manual truck of the same year.

Ok thank you. I did keep my automatic computer, I wonder if this is the problem.

For my 94 truck, which year of computers will work? If its like a from like a 93 or 92 would it still work? Also does the engine have to be the same in the donor truck?

Asking because my local junkyard has a manual truck(the same truck I got my pedals and shifter from) but I'm not sure exactly what year it is. Definitely a 92-94 though.