if I remember right,
@eric 87 found a bad connector plug on the ignition coil after he got into his swap. that could have been the cause of his issues before he started the TBI-to-carb swap. maybe he can provide more details.
The plug was the four wire plug to the ignition module. It wasn't the source of the original issues which had been sorted. BUT in the process I think the shop that did the diagnosis on laptop since my OBD1 port wasn't working.....he found the bad pickup coil. I got the new distributor complete for him to drop in. At this point I had shot the parts gun at it like a 12 gauge and thought why stop now. Well it kinda sorta fixed it....the idle was horrible at times it would drop so low when leaving the shop ( I had to pick the truck up after hours after work) that it died at a traffic light. When I started back up it went crazy on idle to 2500. I was able to go down the road in traffic without giving gas and it shifted from first to second easily. I pulled into a parking lot and restarted. This time back down.
Next day it did this to wife who said and I quote. We keep the truck if its fixed and I do not have to worry about getting somewhere. Spend the money on a new engine. By new we are talking about 6200 for a GM fully dressed including accessories like AC and alternator etc. But me I chose no lets just go carb swap.
I could have done this the way everyone else has and get the distributor, Intake for carb that fits TBI head center bolt angle and holley 600 cfm street warrior. (some parts were chosen because it was Thanksgiving and some parts were not available so I shopped what was)
Let me back up by saying the IAC was replaced and tested twice along with all the other sensors regarding the idle. SO I am not sure the bad plug is what caused this issue but it may very well have been.
The truck then threw a code 42. And my reading of that is ignition module (brand new in new distributor) and I replaced it EVEN though the new distributor I just put in had a new one in it. Nothing changed and clearing code it came right back.
Other cause is fuel circuit has OPEN circuit or short.
Hmm Fuel relay. I mean why would wire go bad but lets be sure. I tested the circuit from ECM to coil. Good. Replaced fuel relay and whatever the relay is (still do not know what it is ) next to it. THey are identical relays. THe fuel relay circuit has the red test wire though I knew this.
Cleared codes and nothing changed. It threw 42 again.
HAD ENOUGH.
THis is when I ordered the parts for the swap. Now into this 700$ or so in TBI. Now 900 for carb swap in parts which now are about 1000-1100 because I have bought parts I am not using now and have gone a different route during the swap in regards to fuel delivery.
When taking truck apart and laying across the top of the engine (what a site that probably was) and taking out the new distributor I unplugged the 4 pin wire to said ignition module and I counted 3 out of 4 female pins inside the plug. That nice new copper was looking at me as if mocking me.
PIN number 3 was not there. Did it come off when he replaced the distributor or when I replaced the module? Was it the cause of the idle all over the place or was it the cause of code 42 which I got because I put a new bulb in dash for the SES light! I think it was probably when he put in the new distributor. Only because the missing issues had cleared up. When sitting at his shop running it was smooth before I took off. OH I was so happy initially. Two traffic lights later not so much. But since the bulb was bad in my dash I didn't know it was throwing a code and he would not have either. He was using a laptop anyway so he had it going. Either way I am now sitting here at 430 am typing.
I still haven't completed this. I have taken many left turns in this swap. I do not want this to be just a work around job. I want it to end up performing good and looking like it came from the factory like this.
I am going to remove the entire computer IF and only IF it runs good. I will finish it up to my standards. That includes all extra wires gone. The TBI stuff will be sold since it is all new including intake and TBI that was rebuilt and distributor.
IF it is marginal I will sell the truck as it is with all the plugs intact and directions to undo what I have done should the next person want to revert it back and just replace that plug and roll the dice.
I will update. I HOPE to have it running by end of day. I got the wrong pressure regulator in the original shipment from Summit. So now I am using a holley low pressure inline pump cut power to in tanks. Found the prev owner rigged the 6 port valve and bypassed it using only the drivers tank. Right has vanish smelling gas in it. Using a primitive 3 port single wire aux tank selector valve. No return line since pressure is low to carb. Dash switch will just be for sending unit use since I am deleting the selector valve that has the switch in it for the sending units. I have a toggle bottom edge for the new selector valve. ON it uses right tank OFF it reverts without power to left tank. Have to wire my electric choke and solder all my wiring today distributor cap back on and plug wires. OH and I have to do something about that bad gas in right tank.
If truck runs good on left tank today I will ultimately order a new wiring harness for a 70's or 80's truck with AC and rewire. IT has a th400 so no worries on that. I will put in new tanks with no return line sending units. My 87 will revert to an earlier year.
Would I do this again. Sure. Maybe not if I caught the plug issue and it fixed the last bits. However one plus is that all these parts will fit (except intake I suppose) a new long block if I keep the truck and it needs it down the road. Then I have these parts and I still save money long term.
So far wife is on board.
As long as end product she can get in and feel as if she can drive anywhere and back with confidence. Even a new long block. I figure even with a new engine my cost to what the market is bringing for solid trucks original or resto mods is still safe. But if I do all this I will not be selling. Just feeling comfortable about spending it on this truck. As of now I am still invested less than 20k. A long block might put me just over a bit.
Sorry to be long winded but felt a good description and heads up to not only check wires but the plugs themselves because I was back pinning while doing my tests on wires.
