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The GAC Truck

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More progress on the TBI swap:

IMG_20191113_150534.jpg

Unfortunately, I think the ECM might be toast. It isn't activating the fuel pump relay. I have verified the fuel pump and wiring works with the red jumper connector at the relay, I can also jumper out the oil pressure sensor connector and get the pump the run.
Even with the relay jumpered out, it still won't fire the injectors. I can get it to run with starting fluid so I know I have spark but no fuel pump or injectors firing... I'm thinking ECM, thoughts?
 
Last edited:
Chevy305 said:
More progress on the TBI swap:

View attachment 320756

Unfortunately, I think the ECM might be toast. It isn't activating the fuel pump relay. I have verified the fuel pump and wiring works with the red jumper connector at the relay, I can also jumper out the oil pressure sensor connector and get the pump the run.
Even with the relay jumpered out, it still won't fire the injectors. I can get it to run with starting fluid so I know I have spark but no fuel pump or injectors firing... I'm thinking ECM, thoughts?
Click to expand...
I would be inclined to think so
 

It runs!!!!!!

Turns out I missed a splice in the harness and the ECM wasn't seeing ignition 12v+ signal. Fixed the splice and it fired right up!
I just need to get a proper throttle bracket and install the O2 sensor and I can be driving down the road.

Next summer I'll actually swap in the ESC distributor. I'll plow this season as fuel only TBI.
 
More progress! Got a bunch of odds and ends wrapped up like the O2 sensor, throttle bracket, and wiring wrapped up.


I drove it to the gas station and it runs and drives great! Idle is more stable and I picked up some more mid range power. It's not as smooth as a factory TBI truck but I didn't expect it to be with the carb intake, adapter, HEI distributor, and the cam isn't the same as the TBI ones. However, I will say it's better than the Holley and the Qjet I had on there especially during cold start and warm up.
The only weird thing is the idle is a little low when warm. So I just looked up the procedure to set the idle so I'll do that when I get the time after the snow storm tonight and tomorrow.

I'm very happy that she's ready to go:

IMG_20191201_105419.jpg
 
I have a TBI intake, and cam that will be coming out soon if you want. Free to a good home, or bad home, or whatever.
 
79rustyk10 said:
I have a TBI intake, and cam that will be coming out soon if you want. Free to a good home, or bad home, or whatever.
Click to expand...
Thanks but I have a TBI intake for it on my work bench. I threw an adapter on it because it was easier than swapping the intake... Lol


On a side note, the GAC truck plowed flawlessly today. :woot:
 
A little update on the GAC truck.

The TBI kicked ass all winter. The only quirks that have shown up are a sticky throttle cable and it sometimes idles low around 500rpm or so while warming up but not quite at full operating temp. I'm going to replace the throttle cable and go through the idle speed adjustment to hopefully work these things out.

Unfortunately the fuel pump is failing though... I was using it to move some loam around the yard and it wouldn't stay running. The fuel pump sounds like it's groaning and it's only making 9-10 psi at best. I confirmed I'm getting full voltage at the pump with a good ground. Amazingly 9-10psi is enough to fire the injectors and move the truck around so at least I got back to a spot I can drop the tank. The pump is from Rock Auto and has a lifetime warranty so I've already got one coming.


Before the pump failed I pulled a stump with her. First pull I broke an old 2" strap. I replaced it with a 3" strap and it was like it wasn't even there. The funny thing is that the frame flexes more than the suspension...

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So I changed the fuel pump and still only getting a little more than 9 psi. The pump sounds a lot better though.

IMG_20200529_160342.jpg

The tank was still brand new inside without a spec of dirt or rust so I don't think the fuel filter is the problem. If I pinch down on the return line I can get up to 15 psi. Any TBI experts out there can give some advice?
 
weak spring in the regulator . i remember reading a lot that most were 10.5 to 11.5 psi and some lower . old @eagle mark said 13 was best i think for a stock tune . . . ?

also you check voltage drop at pump from relay to see if bad wire . also check ground again . if there not tight you might not be getting full power .
 
GAC Truck update:

So earlier this spring I had been having fuel pump and pressure issues with the TBI swap. I replaced the pump in a previous post and it didn't really fix the problem. It came to a head when I was clearing some fallen limbs after a storm this summer from the end of my driveway. I loaded the limbs into the truck and went to turn out to dump them in the woods and the truck suddenly died while I was perpendicular across the driveway. Thank god I didn't try to turn around in the street! After some troubleshooting I found a blown fuse for the constant ECM power which also powers the fuel pump and relay. I had a 5 amp fuse in there because that's what I thought it's supposed to be based on some schematics but the fuse wasn't blown like a hard ground fault, it was more of a slow melt from over current over time. I put a 15amp fuse in it's place and instantly the fuel pump sounded way better and I was getting consistent fuel pressure although still about 9.5psi.

I figured the regulator spring might be weak so I rebuilt the throttle body and shimmed the spring with a washer. Now I get about 10.5-11psi which is still low but it's significantly better. I also adjusted the idle set point finally and it's sooo much happier now. I set it slightly high to 800-850rpm to help with the plow pump speed. I was going to spend the time to swap in the TBI distributor but now that the truck is running so great I don't know that I will bother before winter.

Also my current project is replacing a rusted out spring hanger on the passenger side. I have been dreading this project and going back and forth on whether or not it's worth it to mess with but given it's condition it's either find a new plow truck or fix what I already have. So I dug into it and I will say it came apart waaayyyyy easier than anticipated. Whoever put this truck together many years ago used antiseize on the spring bolt and it slid right out. I couldn't believe it! I was expecting to have to cut the bolt and remove the spring and press in a new bushing but got super lucky and I don't have to mess with that stuff! For the rivets I cut the head off with a grinder and used and air chisel to pop the rivets out.

Check out the pics, you can see the inner bolt hole was only being held in by the washer that had fused itself to the bracket. It was also completely rusted out going up both sides. I did a quick wire wheel and rustolium spray bomb in the immediate frame area. I'm not going to get carried away with painting because if I'm going to spend time stripping and painting a frame it's going to be on my '12 Silverado. That damn wax coating is completely shot and the frame isn't that far off what the GAC truck looks like...

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My plow truck still needs the front hanger for the rear spring on the drivers side replaced--and the fuel tank,which leaks under the strap closest to the rear,and is in the way of removing the rivets on the hanger anyways so it'd need to be removed even if it wasn't leaking..

The sending unit is not working either,and I have only some spares (one is a brand new one) for gas powered square bodies,I may try swapping the rheostat from one of them to the original diesel sender,that has the water in fuel light and a drain for water made into it (3 nipples VS 1 on a gas sender)..but I may have to just buy one,because I think the sending units I have are for a passenger side tank,and they are different for right & left..they are expensive too,almost 90 bucks..:(

I'm dreading having to get that leaf spring bolt out of the bushing,I'll probably have to remove what is left of the hanger first and lower the spring down so I can get a socket on the nut...I'm sure no one has messed with the springs on this truck since it was new,and my frame is about in the same shape as Chevy 305's is..the hanger was worse!..

I have several new spring bushings my friend had left over from replacing spring shackles at his shop he gave me ,that look like the right size,I am hoping I wont have to resort to using them though--it sucks getting the old bushing out and sucks worse trying to install it without cracking the "eye" of the spring..

I got a "new" spring hanger ,my brother came across a truck in NH like mine in a salvage yard that had one replaced recently and it was bolted on,and he was able to get it off,the spring bolt came right out,and its in nice shape--still has paint on it..mine was completely separated along the side facing the rear tire,at the bend where the rivets are.and all the way around the bottom,and partway up the other side next to the fuel tank..

I have a hunk of thick angle iron bolted to what is left of it and a old cab frame mount I had, to cob it together "for now"--had to drill out some of the rivet holes to 1/2" for the new bolts,--the only thing holding the hanger from tearing right off was two or three rivets on the fuel tank side--it was rotted all the way around,up to those rivets,its a miracle it didn't just rip right off while driving,it could have punched the fuel tank too!..:eek:

I've put off fixing it too long,and its getting dark earlier every day and colder out...not looking forward to this job,and I may have to weld a plate to the frame and weld up some cracks and patch a few other areas like where the E brake bracket was riveted to the frame,it tore out the rivets ,leaving a slot,I bolted in a new bracket I made,but should zap a patch on that area--not sure I can even get at it with the bed on the truck though..wish I had some help,I'd yank the bed off it and put the flatbed I had on my '77 GMC on it..
It weighs 900 lbs ,made of 4" channel,my other plow truck plowed great with that heavy bed on it..
 
Long time since an update. It's still kicking, haven't done much to it, just slowly getting lighter with nature's weight reduction. It got bad enough for the battery to bounce out of the battery tray and fell through the rusted inner fender during a storm last year. I bought a new battery tray and inner fender from LMC. Cheap reproductions but not terrible as they did bolt in for the most part. But most importantly it'll get me by for a few more years and probably outlast the rest of the truck.

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Next on the list is a general fluid check, oil change, greasing, and the bigger job will be to replace the driverside caliper as that's sticking right now.
 
Needed to replace the front rubber brake lines as they were cracked and bubbled, and well things escalated quickly...
So the phase "Open a can or worms" should take on a new meaning more like open a can of rusty brake lines.

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