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l29 vortec 7400 swap?

This is a discussion on l29 vortec 7400 swap? within the Engine Swaps forums, part of the Projects and Builds category; Hey guys, I have recently located an l29 truck with 80k on the clock and very complete. I currently have ...

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    l29 vortec 7400 swap?


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    Hey guys, I have recently located an l29 truck with 80k on the clock and very complete. I currently have an l31 in my truck now and am looking to drop the l29 in. I have already searched on FSC,google etc and the info i have found has helped answer alot of questions i had but im still unsure of a few things about the wiring really. Basically i have access to all parts from the truck but the vehicle is far from my house and would like to snag all necessary items in one shot so i guess im going to grab the engine,harness,computer,radiator,all hoses,all aditional cabling,motor mounts and possibly the hydroboost setup? Do i only need to replace the harness in the engine bay up to the bulkhead connectors on the firewall or do i have to go beyond? The vehicle its coming from is a 1997 3500 suburban l29 2wd and the vehicle i want to put it in is a 1998 ecsb 1500 l31 4wd. I'm not interested in hacking up my l31 harness to run the l29 as i have heard this is an option. I have looked over the engine bays and most of the electrics all look exactly the same and are in almost the same spot. So is it really as easy as it seems? Like as in remove and replace and plug in harnesses where they belong and have a nice day? Also I know that my 4l60 will bolt up but which converter should i use? and if i use the l29 converter will the snout fit the 4l60? I know that the 4l60 will eventually grenade behind the l29 but i just want to use it up and then switch to the 4l80 later.

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    Re: l29 vortec 7400 swap?

    That L29 PCM is going to be expecting a 4L80E behind it, be looking for the inputs from it, and expecting the outputs from it.

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    Re: l29 vortec 7400 swap?

    yea you may have to have the ECM programmed to get rid of its expectancy for the 4L80E...shouldnt be a hard swap otherwise though!

    2004 GMC Sierra SLE Z71 rcsb, 5.3/4L60E/3.73/G80 time bomb...3" lift, tinted 03+ Silverado tails, plasti-dipped 16" wheels (unknown brand), 285/75/16 Thunderer M/T Extremes, Thrush Welded muffler...

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    Re: l29 vortec 7400 swap?

    If finances aren't a constraint, get the 1997 column and dash harness while you're at it, so you can be rid of the rotten Passlock system your 1998 model has. When you have the dash and engine compartment harness along with PCM from the donor truck, you're in a much better position to swap.

    You'd also be far, far better off going ahead with the 4L80E swap instead of attempting to modify for 4L60E just to undo that later when it explodes.

    Richard

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    Re: l29 vortec 7400 swap?

    yea, in 10,000 miles or so when it explodes...lol

    2004 GMC Sierra SLE Z71 rcsb, 5.3/4L60E/3.73/G80 time bomb...3" lift, tinted 03+ Silverado tails, plasti-dipped 16" wheels (unknown brand), 285/75/16 Thunderer M/T Extremes, Thrush Welded muffler...

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    Re: l29 vortec 7400 swap?

    OK update on the l29 suburban. spent the day trying to get it running before purchase. maf harness and maf were missing so i replaced both from a l31 tahoe. removed alarm/remote start module correctly,re hung the serp belt which was off for some reason,dropped in a fresh interstate battery, checked fuel pressure through schrader valve which shot like 5 feet out lol,found a couple of plugs unplugged on the engine so i plugged those back in, checked all relays and fuses and replaced what needed to be replaced and after all that still healthy crank but no start condition. I pulled the front spark plug on the passenger side and checked for spark by grounding and cranking and there is no spark. Whats weird is spoke with the owner of the yard and he said the truck drove and ran fine three weeks ago when it came into the yard, So what happened from then till now? only thing i can think of are coil,crankshaft position sensor,ecu everything else looks fine and unscrewed with. any ideas guys? i want to snag this thing before it becomes a parts mule for like 5309038452309 other people.

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    Re: l29 vortec 7400 swap?

    well can you snag parts (even temporarily) from other GM's in the yard to try and get it running? if not, the only other way i'd buy the engine is if you run a compression test on it. if it passes a compression test well, then you can use the whole "it won't run" thing as leverage to get the price down and mess with the no spark issue when you get it home.

    2004 GMC Sierra SLE Z71 rcsb, 5.3/4L60E/3.73/G80 time bomb...3" lift, tinted 03+ Silverado tails, plasti-dipped 16" wheels (unknown brand), 285/75/16 Thunderer M/T Extremes, Thrush Welded muffler...

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    Re: l29 vortec 7400 swap?

    Since the coil and module are nearly invisible on the big block, climb up on top and be sure that sumbitch is still back there. They bolt on a bracket to the rear side of the plenum, facing the firewall, you practically have to lay down across the intake to see them. You'll also have to check by braille that the distributor is still plugged into the harness.

    Richard

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    Re: l29 vortec 7400 swap?

    I checked the coil setup and distributor like you said and everything is there. I even went as far as to remove another coil setup from that l31 tahoe next to it and plug everything in and still no spark. the only thing I'm unsure about is when I use the l31 coil setup the bracket is different so i couldnt bolt it down to anything and I'm not sure if the bracket needs to be grounded to the block. I'm beginning to think this is most likely a crankshaft position sensor issue.Also instead of checking for spark at spark plugs how to I actually check for spark at coil? Can i just take a spare spark plug and wire and plug it into the coil output and ground it during crank? I feel like I'm close to firing this beast up but just cant determine exactly whats going on. Some people have mentioned that i can put a code reader on the obdII and even with a no start condition pull codes for possibly what is wrong with it.I have thought about swapping in an l31 ecm but I heard that if you swap ecms you have to do a relearn and I dont think any of that will help me.

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    Re: l29 vortec 7400 swap?

    I bought a '98 5.7 parts truck that ended up having a bad module; drove it around the lot many times with a spare coil/module sitting on top of the engine - but I did use an alligator clip test lead to ground it to the engine. Not sure if it really needed it but you might try.

    Richard

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    Re: l29 vortec 7400 swap?

    OK, I figured it out, crankshaft position sensor was missing so threw one in and it fired right up. Thanks for the help guys

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    Re: l29 vortec 7400 swap?

    Missing! Would be an issue.

    You might want to check it after a little runtime; there's a known issue with the reluctor wheel kissing the crank sensor, requiring shimming to increase the air gap. Replacement sensors will come with a couple thin shims.



    Richard

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    Re: l29 vortec 7400 swap?

    glad you got it going man! can't wait to see this project progress!

    2004 GMC Sierra SLE Z71 rcsb, 5.3/4L60E/3.73/G80 time bomb...3" lift, tinted 03+ Silverado tails, plasti-dipped 16" wheels (unknown brand), 285/75/16 Thunderer M/T Extremes, Thrush Welded muffler...

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    Re: l29 vortec 7400 swap?

    Yeah, can you believe it? The crankshaft sensor of all things. Its another situation of people taking all the wrong stuff and leaving all the right stuff at the yard which entitled me to yet another head scratch at the junkyard....Thanks for the kind words and good info! I'm really not sure what to expect dropping in a low mile L29 into a half ton truck, I suppose as long as ends up being better than before then its a good starting point. I have already gone ahead and swapped in a 14sf 6 lug 4:10 G80 out back so the gearing should help get it going and I already emailed blackbear about a pcm tune in accordance with the odd L29/4l60 combo and a couple other changes and im hoping he can do it, just waiting to hear back now. I have been poking around for a whipple for it but i guess the 7.4 ones are kinda rare and the prices that they are usually sold for i may end up going rear mount turbo.

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    Re: l29 vortec 7400 swap?

    I put an L29 7.4 into a truck that originally came with a 6.5TD (1994 3500HD.) The gas engine option for that same truck would have been a TBI 7.4.

    With the NV4500 trans, 4.63's in the Dana 80, and 33" tall tires (245/70/19.5)...I think it was a wise choice.

    Richard

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    Re: l29 vortec 7400 swap?

    OK, Have another quick question. I took a look at the big block motor mounts today and the bottom parts are welded to the frame then the brackets that bolt to the engine just bolt to the welded brackets on the frame. the big block is in a 2wd truck and my small block is in a 4wd, am I going to get into trouble with the mounting situation or will everything bolt up?

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    Re: l29 vortec 7400 swap?

    Alright so i was able to retrieve the motor harness torque converter all accessories harness and the entire loaded core support.I have found someone locally selling a 4l80 with transfer case on the rear so I think I am ready to jump on that but now comes the issue of harnesses. The harness from the donor truck is l29/4l80/2wd, the harness from my truck is l31/4l60/np243 and i have since located an l29/4l80/np241 harness from justchevytrucks.com. The real issue it seems is no matter what I do the final harness is going to be a modified one because I really dont want to give up my push button 4wd and I guess they never offered push button 4wd behind a 4l80 trans. My current options are: mod my harness to run big block and mod it to run the 4l80 and have to do no mods for the transfer case wiring, get the harness from justchevytrucks.com which will be correct for big block and 4l80 but has no wiring to run the np243 push button transfer case which after looking at my factory service manuals cannot be properly wired stand alone as it runs through the vcm. I guess I am going back to the junkyard to grab an l31/4l60/np243 harness and chop the **** out of it and get it all set up for my new strange combo of l29/4l80/np243. Has anyone actually run that particular setup? pics or info would def be appriciated at this point

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    Re: l29 vortec 7400 swap?

    so hows the build going? havent updated in a fwe weeks. excited to see the final out come as i am looking into getting a 99 k1500 suburban and planning on swapping am 129 into it with the 4l60e until it blows.

 

 

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