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desertjoe 
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 Topic: Calling the TBI Experts,,,,
Posted: 22 Jun 2023 at 11:33pm |
OK, I bought a 1988 GMC 3500 with the 454 engine and Turbo 400 couple of weeks ago and finally drug it under my work area,, Suppossedly it was "Running When Parked" but the owner tol;d my brother that the 454 was in great running shape The engine has a Throttle Body on it and I'm assuming it does have the HP pump in the tank,,,?The engine will start and run when you prime it but will stop soon as the fuel is burned in the TBI,,,, SO many hoses in the way to tell if there is a manual fuel pump on block,,,,?? Any suggestions out there before I start dismantling?
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DaveKamp
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Joined: 12 Apr 2010
Location: LeClaire, Ia
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Posted: 22 Jun 2023 at 11:42pm |
You're certainly not getting fuel flow.
The throttle body unit was made by Rochester for GM, and it's referred to as the TBI 220, and will probably have a pair of 45lb/hr injectors. The fuel pump needs to develop around 15psi for this IIRC, and there's usually NOT a fuel pump on the block. The TBI-220 has a pressure regulator and a fuel return line that sends unneeded excess back.
The ECM that runs this system is referred to by four digits of it's model, it SHOULD be a 7747 controller, uses an EPROM chip with all the mappings.
The fuel pump is PULSED by the ECM, so it is possible that your TBI and injectors are fine, and you're just not getting a power signal. USUALLY the 7747's FUEL PUMP output drives a fuel pump RELAY... and you'll know it's working when you turn the key on and hear the pump run for about 4 seconds or so.
You can pull the high side line off the TBI-220, place it over a bucket, and cycle the key several times which will clear out the old gasoline... but after you've done that, connect it back up. The startup process should pressurize the system and trigger the injectors a couple times. This clears any air bubbles and 'primes' the engine for a cold-start.
Once you're cranking, if the 7747 isn't getting an IGNITION pulse, you won't get an injector pulse, so check the electrical trigger from the ignition to the ECM... if that's disconnected or bad, you won't get injectors firing in the TBI during cranking.
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Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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Dirt Farmer
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Joined: 15 Sep 2020
Location: Illinois
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Posted: 23 Jun 2023 at 12:11am |
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It may never run again Joe, better just send it my way and leave those worrys behind, kinda partial to them square bodies. Not that it matters for this but is it 4wd? Ok joking aside, the fuel pump is in the tank on that model with fuel injection. First confirm that there is gas in the tank, dont trust the gage. If you turn the key in run position you should hear the pump running if not take off the gas cap and listen. If you dont hear anything first check the fuse box for a blown fuse or relay, if all checks ok there then tap on the bottom of the fuel tank with a board or rubber mallet and see if that frees the pump up. That trick only works once or twice to get you home then its replace the pump time. To replace the pump if the tank is less than quarter full I pull the tank, if its more I lift off the bed and reguardless DO NOT use drop lights with glass bulbs when removing the fuel tank. One wrong splash and not good results. A truck of that era probably needs the whole sending unit replaced as the lines may be brittle from rust if you have to take it apart anyway. Just be careful and if you give up on it and throw in the towel I may be up for a road trip with my trailer. Keep us posted and include a photo. Dave and I must have read this at the same time but hes faster than me and knows his stuff
Edited by Dirt Farmer - 23 Jun 2023 at 12:18am
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8070nc
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Posted: 23 Jun 2023 at 4:48am |
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I know this is uneeded informatuon but I have a 1988 3500 4 door that was originally a air force rescue vehicle. 454 np 205 cast irn transfer case
Dana 80 rear dana 60 front. Its geared 4.56
Came with a turbo 400
I change it to a4l80e because with the turbo 400 it was turning 3000 at 55 mph. It willbe the last thing to leave my place
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1984 80780
1957 D14
DES 300 with 25000 engine
616 tractor
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Thad in AR.
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Posted: 23 Jun 2023 at 5:49am |
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The ignition module in the distributor triggers the injectors. Seen many fail.
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im4racin
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Posted: 23 Jun 2023 at 6:31am |
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This is should clearly a fuel only issue. The distributor is sending a crank signal since it runs until the priming fuel he put in intake is gone.
Edited by im4racin - 23 Jun 2023 at 6:31am
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Thad in AR.
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Posted: 23 Jun 2023 at 6:43am |
 im4racin wrote:
This is should clearly a fuel only issue. The distributor is sending a crank signal since it runs until the priming fuel he put in intake is gone. |
Right and if it doesn’t send a signal to the injectors there will be no fuel to burn.
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plummerscarin
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Posted: 23 Jun 2023 at 6:45am |
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Had a similar situation with a 93 V6 TBI. Found a blown fuse on the firewall for the fuel pump relay. Also some bare wires in the throttle body going to the injectors. These wires had the insulation worn off where they pass through the air cleaner base
HTH
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desertjoe
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Posted: 23 Jun 2023 at 6:50am |
It is what I just love bout this site,,,,,always some that have "Been There-Done That" and gives you a place to start!!n I have always been against replacing parts til you find what works,,,cause them parts stores ain't gonna take back the parts you used when experimented,,,,!!! 
Hey 8070,,who dod you buy the electronics conversion for the 4L80e? According to the tag in glove box, that is what this one came with and while I do like the pulling power with todays fuel prices don't think I'm gonna like the 7-9 MPG,,,,,,
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desertjoe
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Posted: 23 Jun 2023 at 8:34am |
Well, I went out early this morning and stuck a long hose in fuel tank, turn key on and the friggin pump runs ALL THE TIME!! possibly PO has jumpered the fuse???? WHY? Anybody know where the fuel pump relay is on this trk? I guess I best check if Orelly has a manual, CHIT ain't fount the fuse box yet,,,,, On the TBI itself, there are two 3/8" hoses going to the backside of the TBI, one on driver side and another on passenger side,,,,which is which??
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8070nc
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Posted: 23 Jun 2023 at 8:52am |
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My truck has a fatory tach. At 55 mph the engine was turning 3000 rpm. With a 4l80e its about 2250. I can live with that. The truck hums along happily. The controller is from tci
Jegs or summit racing has them
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1984 80780
1957 D14
DES 300 with 25000 engine
616 tractor
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8070nc
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Posted: 23 Jun 2023 at 8:54am |
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My fuel pump relay is on firewall just above just above the air conditioner evaporator
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1984 80780
1957 D14
DES 300 with 25000 engine
616 tractor
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8070nc
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Location: North Carolina
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Posted: 23 Jun 2023 at 8:57am |
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I lied. Wrong truck. If yours is a two door its a totally different truck
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1984 80780
1957 D14
DES 300 with 25000 engine
616 tractor
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Thad in AR.
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Posted: 23 Jun 2023 at 9:14am |
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If it’s the newer body style than a square body the fuse box in in the end of the dash drivers side.
Most likely have a fuse box under the hood as well. Relay will be in under hood fuse box or on the firewall.
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ac45dave
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Posted: 23 Jun 2023 at 5:06pm |
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Joe, I've been through this my self on a few of my old units in the past.If I had my guess, the soft rubber hose that connects the top of the pump to the sending unit pipe is most likely rotted away resulting in no fuel pressure.Had this issue on my old 88 GMC that dad ended up with.Also had the same issue with my old 90 Caddy.Luckily he put a dump cylinder on it which made pulling the sending unit easy.Pull the sending unit and check that connector hose.
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54 wd-45gas ; 56 wd-45d N/F w/fact p/s ; 63 d-17 sIII N/F gas ; 60 D14 N/F ; 67 d-17 sIV N/F gas ; 63D15 sII W/F; 39rc#667 ; 2021 massey 4710 fwa ; gravely 2 wheel tractors
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plummerscarin
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Posted: 23 Jun 2023 at 5:19pm |
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My 89 and the 93 has the fuse and relay on the firewall.
The 89 has the supply on the drivers side. A quick search says you should be getting 9 to 13 psi. I thought it should be higher... so be it. Pull the line turn the key and see you're getting fuel to it
Edited by plummerscarin - 23 Jun 2023 at 5:26pm
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desertjoe
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Posted: 23 Jun 2023 at 11:12pm |
OK,,did a lot of trouble shooting today and am not any better than this time yesterday,,,,,  Since the bed is already off the trk, I disconnected the discharge line off the pump and hooked a 1/2" hose directly of the pump discharge into a gallon clear jug and cycled the key several times. Pump would NOT pump anything for 2 seconds and then pump a full stream for 3 seconds then STOP pumping,,,,?? One time, I left key on and after 10 seconds it started the same thing like before,,,,?? Thinking the fuel pump was bad, I got a new pump and installed it ,,,,,and,,,,Same Chit. I'm NOW thinking it is an electrical issue keeping the pump from doing it's job,,,,?? I started thinking maybe the fuel pump relay was the culprit, so after locating TWO relays on firewall next to A/C accumulator, I swapped them around but that made NO DIFFERENCE in fuel pump action. These two relays were way different than any I had seen before. They are twice as big than the standard 1"X1" square ones. After looking some more,, I locate another of these same relays on driver side firewall,,,have NO idea what it controls, tho. Went to Oreillys and Autozone and NAPA and nobody had a manual to get a wiring diagram so gonna look elsewhere tamarrow,,,,? The engine runs fine as long as you spray start fluid into TBI, but will shut down when the spray stops,,,,,, 
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steve(ill)
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Posted: 24 Jun 2023 at 8:27am |
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Im no expert on that particular truck, but on most newer FORD trucks ... when you turn the key ON, the fuel pump runs for 3 seconds to build up pressure in the fuel rail.. That is controlled by the "fuel pressure regulator" and the "computer" ..... After 3 seconds the pump STOPS and just sets there... You can turn the key OFF and back ON and it will run another 3 seconds... You have to CRANK the truck to get the system to start cycling the pump on and off to Maintain Pressure.
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Like them all, but love the "B"s.
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DMiller
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Posted: 24 Jun 2023 at 11:15am |
With engine running is a Oil Pressure Override to the Start pump bump, gives continuous power to fuel pump, also stops it if engine dies or as in a crash loss of oil pressure. NO Oil Pressure and NO Pump.
Rail Pressure regulator in usually Drivers side top Front of Engine at end of the fuel rail where lines connect.
Edited by DMiller - 24 Jun 2023 at 11:15am
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Lars(wi)
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Posted: 24 Jun 2023 at 3:45pm |
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If the fuel pumps is running constant, without the engine running, wouldn’t that indicate your empty of fuel, or the pump won’t build psi?
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I tried to follow the science, but it was not there. I then followed the money, and that’s where I found the science.
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desertjoe
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Posted: 24 Jun 2023 at 8:07pm |
IT RUNS,,,,IT DANG SURE RUNS!!!! That 454 sounds great and starts right up,,no strange noises and NO SMOKE out the tailpipe,,,YEAH,,,,!!! I started after the problem early this morning and did what I like to do by process of elimination and ole Thad's suggestion of it being the ignition control module was the most likeliest culprit. Another concern is that the PO had installed 4 different Jumper wires in engine compartment for different things and then cut them and left ends bare,,,well, while trying to install the new ICM ,,,one of them friggin bare wires shorted and burned the fuse. Taped the wire end up, and fired that mother up,,,,,!!!!
I want to ""THANK"" all of the guys that helped with this project!!!!
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Thad in AR.
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Posted: 25 Jun 2023 at 5:34am |
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Glad to hear you got it going.
Now keep us updated on your progress with it.
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desertjoe
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Posted: 25 Jun 2023 at 7:44am |
Yeah Thad,, and I am stoked on the actual condition of the 454!! I adjusted the timimg a tad last nite and starts and runs much better.and after getting a couple of flats fixed I'm raring to get the trk on these backroads and try out the T400 for it's condition,,,(fingers crossed) I did buy the trk "NO Title" as was sold as a parts trk but I've found most times the owners have "lost" the title and just do not want to look for the title. I have bought three other vehicles as No Title and that was the case, but was able to get a titla with a bond. The PO tells me he knows the registered owner and is positive the trk is not stolen or tied up in divorce, so I will hold on spending more til I get word from him. I have had luck with buying a Bond thru my insurance Co and let them do the legwork to produce a title in my name from MVD. Got my fingers crossed on this one as I plan to do a quickie restore to use it as my tow vehicle instead of the (gasp) F150 I now use,,,PLUS may even make ole Shameless more friendlier with me,,,,,
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SteveM C/IL
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Posted: 25 Jun 2023 at 1:55pm |
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Just have a big fuel budget...my 95 7.4 TBI hovers around 7-8 mpg short tripping....will push 11 on interstate at 65 empty.
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desertjoe
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Posted: 25 Jun 2023 at 4:10pm |
Well Steve,,I knew that little tidbit was gonna come up sooner or late,,but here's the way I'm, looking at that,,,,,My alternative is to contiue to use the F150 Half Ton with the small 5.4 engine and have to lug it down the road while it's drinking a healthy amount of fuel,,, most likely 7-9 MPG,,, or use the One ton with the 454 most likely also drinking 7-9 MPG and doing it at a much better pace,,,,??
One other thing for those guys here that are experts at finding hard to find parts on internet I have the current catalog from LMC Truck and the 3 items I need are not listed in their catalog,,,?
I had to remove the white plastic turn signal assy on the steering column with the long wire harness down to it's connector under the dash and when I tried to disconnect to remove it from the steering column the plastic 10 wire connector just totally disintegrated in my hands and LMC does not list them.
Does anyone know of another outlet for squarebody parts??
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bemer848
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Posted: 25 Jun 2023 at 5:38pm |
Joe look on rockauto.com. If it is what I think I see one for $20
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Thad in AR.
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Posted: 25 Jun 2023 at 7:01pm |
desertjoe wrote:
Well Steve,,I knew that little tidbit was gonna come up sooner or late,,but here's the way I'm, looking at that,,,,,My alternative is to contiue to use the F150 Half Ton with the small 5.4 engine and have to lug it down the road while it's drinking a healthy amount of fuel,,, most likely 7-9 MPG,,, or use the One ton with the 454 most likely also drinking 7-9 MPG and doing it at a much better pace,,,,??
One other thing for those guys here that are experts at finding hard to find parts on internet I have the current catalog from LMC Truck and the 3 items I need are not listed in their catalog,,,?
I had to remove the white plastic turn signal assy on the steering column with the long wire harness down to it's connector under the dash and when I tried to disconnect to remove it from the steering column the plastic 10 wire connector just totally disintegrated in my hands and LMC does not list them.
Does anyone know of another outlet for squarebody parts??
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I assume you need the whole turn signal assembly?
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Thad in AR.
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Posted: 25 Jun 2023 at 7:10pm |
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Joe I googled 1986 Chevrolet Silverado turn signal switch and lots of them came up. Even most auto parts stores may have them.
I I typed 1986 rather than 1988 as only 1 tons were square bodies in 88.
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desertjoe
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Posted: 25 Jun 2023 at 10:44pm |
The only'ist reason I was removing the turn signal assy is the PO told me they had tried to steal the trk and used a grinder to cut around the ignition key and ruined the black metal housing that covers the whole key area. I had a spare metal housing left over from some other project and the turn signal and wiring harness has to come out to change the housing out.,,, I'm getting some "FRUGAL" ideas to reuse the old one and just solder in a couple of 5 prong connectors to get the 10 wires taken care of ,,,,nuttin wrong withy the turn signal assy,,,just plastic connector destroyed,,,,,I'ma check out Autozone / Oreillys anyway,,, More than one way to skin a cat,,,,??
As an update on the Budd wheels and tires I was looking for,,I also won a bid on the Marketplace this morning for 6 Budd wheels mounted up with almost new caissons with only 500 miles on them ,,,,,,,,for $300,,,, I was not holding a gun on the dude when he gave me that price,,,,,,,,,,,,
MANY Thanks for all the help,,,,!!!
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Ray54
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Posted: 26 Jun 2023 at 10:58am |
For what ever reason O'l GM had to make 101 different variations on all the pieces on the steering column. I spent a year finding the right switch mechanism for a 75 Chev C10. I used cotter pin remover tool for a year to start it with the switch just hanging. Other than needing 2 hands it worked real good.
Then years latter I put a steering column from a 75 GMC 1/2 ton in it ( no idea why I did it today  ). I just know even thought the plugs fit, it set the horn to blowing. I need to give that gem to Joe it could take all his time so he would not have time for those women chasing him. Or he could just go off and leave it sit like I am doing. But it was not women that kept me from it, just the other cheap Chevy trucks sitting around here. 
But from watching Joe this truck will not stop him unless other things are more interesting. But heaven help the next guy trying to find what parts he substituted. |
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