98 l29 454 mystery

[Lennyobs]

Finally swapped in the l29 got the motor running and driving idles by itself but motor has a heavy misfire.
Truck is a 96 harness 96 from the old 5.7 modified for the l29 ecm is 98 with the 4l80 repinning runs thru all gears fine, when I pull out plug wire #1 & #8 no change in idle or revved above 1000rpm. Checked injectors and any air or vacuum leaks, redid timing about 5 times. Can’t figure it out

 

[andy396]

How’d you modify the ‘96 350 harness for sequential port injection? (admittedly I’m not familiar with SBC L31 Vortec fuel injection) Are you batch firing the injectors? If you put the trigger wire of a timing light on each plug wire does it show it’s getting spark?

What was the condition of the L29? Collapsed lifters, broken valve springs? What’s fuel pressure look like? New or old injectors? How’d you check them?

 

[Lennyobs]

How’d you modify the ‘96 350 harness for sequential port injection? (admittedly I’m not familiar with SBC L31 Vortec fuel injection) Are you batch firing the injectors? If you put the trigger wire of a timing light on each plug wire does it show it’s getting spark?

What was the condition of the L29? Collapsed lifters, broken valve springs? What’s fuel pressure look like? New or old injectors? How’d you check them?

Yes timing light shows spark not sure if they are batch style firing i soldered all corresponding wires color matched to the l29 injector harness and used 1 pink ground like I saw in multiple write ups that used the 350 harness the motor itself guy who sold it to me said the rv “Had” 55,000 miles which the internals of the motor did look very clean. All valve springs are good lifters I cannot speak for and fuel pressure haven’t checked and injectors are original I switched them around from cyl 1 & 3 and mis didn’t move to cyl #3

 

[andy396]

If you’re positive the miss is coming from a cylinder not firing, maybe check compression and if that’s good start looking at your injector wiring.

Have you found the factory manuals linked here:


88-95 Service Manuals
https://r.tapatalk.com/shareLink/to...e-Manuals.43575/&share_type=t&link_source=app

Don’t be fooled by the title. There’s ‘96 and ‘98 manuals there. They were a life saver on my project.

 

[Lennyobs]

If you’re positive the miss is coming from a cylinder not firing, maybe check compression and if that’s good start looking at your injector wiring.

Have you found the factory manuals linked here:


88-95 Service Manuals
https://r.tapatalk.com/shareLink/topic?share_fid=40934&share_tid=43575&url=https://www.gmt400.com/index.php?threads/88-95-Service-Manuals.43575/&share_type=t&link_source=app

Don’t be fooled by the title. There’s ‘96 and ‘98 manuals there. They were a life saver on my project.

thanks bud! I’ll keep updating as I go

 

[Supercharged111]

454 injectors suck, you may be battling something unrelated to the swap.

 

[Lennyobs]

If you’re positive the miss is coming from a cylinder not firing, maybe check compression and if that’s good start looking at your injector wiring.

Have you found the factory manuals linked here:


88-95 Service Manuals
https://r.tapatalk.com/shareLink/topic?share_fid=40934&share_tid=43575&url=https://www.gmt400.com/index.php?threads/88-95-Service-Manuals.43575/&share_type=t&link_source=app

Don’t be fooled by the title. There’s ‘96 and ‘98 manuals there. They were a life saver on my project.

Checked out injector wiring everything looks right both ground all injector wires have signal. Something tells me it might be the ecm which is a 98 & the truck is a 96 tried to find 96 sheet on the link you sent but couldn’t find to compare between 98 & 96 ecm plugs

 

[Lennyobs]

These are the harnesses

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[Lennyobs]

Got the spread from lextech I’m gonna go ahead and 0411 the truck and get local race shop to throw a file on it

 

[Supercharged111]

Like I said, don't overlook the possibility of 2 junk injectors. Did you have a chance to see how it ran before you put it in your truck?