1987 Burb TBI to carb swap

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Oaasport

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I am going to start gathering parts for my 1987 Suburban TBI to carb swap. So far heres what i am looking at. 1985 carbureted tank, fuel sending unit and fuel lines. Also have HEI dizzy and of course intake manifold and carb. Having a harness made to run new carbed engine without all the extra tbi stuff. Now for questions. Will my fuel gauge work with 1985 Sending unit in place of TBI sending unit? Can i use just the 1985 Sending unit in the 1987 tank to save some money? If so, im assuming i just use return fuel system and put on a regulator? I never have done a tbi to carb conversion and ive searched but havent found any direct answers
 

Bextreme04

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I can't fathom why anyone would ever want to do this... it has zero benefit and is going to be an absolute nightmare.

That being said, you are making this way harder than it needs to be. You don't need to swap anything in the fuel tank. An 87 350 should have a mechanical fuel pump boss, so you just need to buy a mechanical fuel pump and pushrod and install it on the engine. Disconnect the electric fuel pump power(either fuse or relay) and then plumb hardline from the mechanical pump into the original fuel line. The mechanical pump will have no issue pulling straight through the electric fuel pump. Make sure you get a three port mechanical pump so that you have a return line to prevent vapor lock. Don't just disconnect the fuel pump connector near the tank or you will lose the fuel level sender signal.
 

Oaasport

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I am doing it because the TBI engine is worn out and i have a fresh built 350 with Vortec heads and all new accessories. The TBI to Vortec manifold is $500, and then a tune, bigger injectors and higher flow pump will near put me at the cost of a used 6.0 engine. Thanks for the help, i greatly appreciate it!
 

C10MixMaster

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I can't fathom why anyone would ever want to do this... it has zero benefit and is going to be an absolute nightmare.

That being said, you are making this way harder than it needs to be. You don't need to swap anything in the fuel tank. An 87 350 should have a mechanical fuel pump boss, so you just need to buy a mechanical fuel pump and pushrod and install it on the engine. Disconnect the electric fuel pump power(either fuse or relay) and then plumb hardline from the mechanical pump into the original fuel line. The mechanical pump will have no issue pulling straight through the electric fuel pump. Make sure you get a three port mechanical pump so that you have a return line to prevent vapor lock. Don't just disconnect the fuel pump connector near the tank or you will lose the fuel level sender signal.


pulling through the in tank pump can lead to vapor lock issues. however the pump could be replaced with piece of hard line and a filter sock.
 

Bextreme04

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pulling through the in tank pump can lead to vapor lock issues. however the pump could be replaced with piece of hard line and a filter sock.
Have you ever actually seen that? I'm pulling through an EP381 and haven't had any vapor lock issues. The design of the pump shouldn't cause there to be much restriction to pulling through it.

Alternatively, you can just keep the in-tank pump and electric pump and run an adjustable regulator. A stock TBI pump only runs 12-14psi anyways, so its easy to regulate it down to the 5psi you want for your carburetor without putting any extra load on the pump. Since you have a fresh 350 with vortec heads, you might have a later block with no mechanical pump provision or a roller cam with no fuel pump eccentric anyways, so just using the factory TBI pump might be the best option regardless.
 

Oaasport

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The block is a 1979 block, mechanical pump. Thats why i was looking into find a carb tank lines and sending unit
 

C10MixMaster

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Have you ever actually seen that? I'm pulling through an EP381 and haven't had any vapor lock issues. The design of the pump shouldn't cause there to be much restriction to pulling through it.

Alternatively, you can just keep the in-tank pump and electric pump and run an adjustable regulator. A stock TBI pump only runs 12-14psi anyways, so its easy to regulate it down to the 5psi you want for your carburetor without putting any extra load on the pump. Since you have a fresh 350 with vortec heads, you might have a later block with no mechanical pump provision or a roller cam with no fuel pump eccentric anyways, so just using the factory TBI pump might be the best option regardless.

I have actually been chasing vapor lock on my truck , when the outside temp hits 95+ degrees you can watch the fuel pressure drop to nothing on a hard acceleration or sometimes just pulling away from a light. Adding any resistance in the suction side of the fuel pump is not good. Might get away with it might not just good to know it can cause a problem. I do agree that using the existing in tank set up with a regulator is probably the way to go.
 

eric 87

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The block is a 1979 block, mechanical pump. Thats why i was looking into find a carb tank lines and sending unit
did you get yours figured out. I have an 87 305 TBI that I am getting ready to change. When you have everything replaced new including computer and you still have issues you finally get to a point either keep it or sell it. Losing 1 mile per gallon or something will not bother me. I and my mechanic both think there are conversions for the fuel tanks that take the pumps out and then just use a carb rated electric. The TBI pumps have too much pressure for a carb and those regulator set ups I am not sure are that good. I think for me there might be after market intakes that have the proper bolt angles for the heads. Not sure why so many are so adamant about the TBI. It isn't like the 86 trucks were horrible. The Computers and TBI comes in 87. And mine has been a nightmare. Thank goodness my mechanic isn't a part gun guy but I have been in order to get to the bottom of it.
 

eric 87

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I can't fathom why anyone would ever want to do this... it has zero benefit and is going to be an absolute nightmare.

That being said, you are making this way harder than it needs to be. You don't need to swap anything in the fuel tank. An 87 350 should have a mechanical fuel pump boss, so you just need to buy a mechanical fuel pump and pushrod and install it on the engine. Disconnect the electric fuel pump power(either fuse or relay) and then plumb hardline from the mechanical pump into the original fuel line. The mechanical pump will have no issue pulling straight through the electric fuel pump. Make sure you get a three port mechanical pump so that you have a return line to prevent vapor lock. Don't just disconnect the fuel pump connector near the tank or you will lose the fuel level sender signal.
My 87 GMC Sierra 305 TBI block had a mounting but no hole in block for pump pushrod. IN my swap I am using an inline electric. Was going to use in tank pumps but the right one went out and when I took off cover plate for selector valve the prev owner bypassed the valve with the left fuel line. The 6 port valve he had recirculating the supply port back around to the left tank input port. The non working right pump was still attached as were the return lines to each tank. I think the selector valve must have given up and stayed in one tank. Either way this swap would have been done long ago had I not run into these issues. I am taking the computer out completely and will sell the entire TBI set up should someone want it with ALL NEW SENSORS and distributor etc. CHEAP.
I don't hate TBI as a rule. This truck though will never see one again. I spent 700 at least in trying to make it work with new parts. Then took to shop and let him put on laptop. Found bad pickup coil. Replaced. Still dying one minute at stop light low idle next minute on restart idle at 2500. Never went down. Two IAC's two Temps two ign modules O2 sensor TPS new Map New Rebuilt regulator in TBI and new injectors.
At some point you cut bait.
Not a debate but a carb will not kill performance and it takes it back to basics of fuel air and spark.
 

Bextreme04

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My 87 GMC Sierra 305 TBI block had a mounting but no hole in block for pump pushrod. IN my swap I am using an inline electric. Was going to use in tank pumps but the right one went out and when I took off cover plate for selector valve the prev owner bypassed the valve with the left fuel line. The 6 port valve he had recirculating the supply port back around to the left tank input port. The non working right pump was still attached as were the return lines to each tank. I think the selector valve must have given up and stayed in one tank. Either way this swap would have been done long ago had I not run into these issues. I am taking the computer out completely and will sell the entire TBI set up should someone want it with ALL NEW SENSORS and distributor etc. CHEAP.
I don't hate TBI as a rule. This truck though will never see one again. I spent 700 at least in trying to make it work with new parts. Then took to shop and let him put on laptop. Found bad pickup coil. Replaced. Still dying one minute at stop light low idle next minute on restart idle at 2500. Never went down. Two IAC's two Temps two ign modules O2 sensor TPS new Map New Rebuilt regulator in TBI and new injectors.
At some point you cut bait.
Not a debate but a carb will not kill performance and it takes it back to basics of fuel air and spark.
I agree the carb won't kill performance, but it also might not fix your problem. The biggest issue with this whole thing is that you have dropped a ton of money replacing parts that weren't bad. Then took it to a mechanic that had no problem doing the same thing. There is obviously something wrong with it, but just throwing parts at it is the wrong answer. Now after throwing $700 at the TBI system, you are throwing another several hundred dollars at it to convert to carb and maybe fix the problem(but maybe not too... because you still haven't identified the problem). Its not that people are adamant about the TBI, just pointing out that it is still following the pattern of throwing **** against the wall and hoping something sticks. Its going to be real ****** if you drop all this money to convert it and find out you had a mechanical problem with a sticky valve or intermittent vacuum leak that was your whole problem all along.

It sounds like the previous owner did some pretty sketchy repairs also, so who knows what all is going on there. A job like ripping out the harness and converting everything over will be very time consuming and will open up a whole new list of things that can go wrong. Be prepared to have a lot more things go wrong before it all gets straightened out and is back to being a reliable vehicle, especially if you arent an experienced and detail oriented mechanic.
 

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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.
 

eric 87

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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.
 

eric 87

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I agree the carb won't kill performance, but it also might not fix your problem. The biggest issue with this whole thing is that you have dropped a ton of money replacing parts that weren't bad. Then took it to a mechanic that had no problem doing the same thing. There is obviously something wrong with it, but just throwing parts at it is the wrong answer. Now after throwing $700 at the TBI system, you are throwing another several hundred dollars at it to convert to carb and maybe fix the problem(but maybe not too... because you still haven't identified the problem). Its not that people are adamant about the TBI, just pointing out that it is still following the pattern of throwing **** against the wall and hoping something sticks. Its going to be real ****** if you drop all this money to convert it and find out you had a mechanical problem with a sticky valve or intermittent vacuum leak that was your whole problem all along.

It sounds like the previous owner did some pretty sketchy repairs also, so who knows what all is going on there. A job like ripping out the harness and converting everything over will be very time consuming and will open up a whole new list of things that can go wrong. Be prepared to have a lot more things go wrong before it all gets straightened out and is back to being a reliable vehicle, especially if you arent an experienced and detail oriented mechanic.
Nope the reason I have been comfortable doing all this spending 700 on TBI and now 1000 on carb swap parts is that the engine checked out good in the shop. The only part the shop put in was the distributor because he found the pickup coil had no magnet. But compression and leak down and all other tests performed well. And when it wasn't dying at stop light or racing away idle after restart it ran down the road great so my original issues had been fixed.
I am like everyone when it comes to money and it is killing me internally a bit. BUT since I may have stumbled on the issue in this swap I know the trucks engine currently is solid and what I have invested. When I am done with it I could easily sell this thing and pick up a few thousand at current market prices. WHICH is not my intent. But it at least makes me feel safe financially speaking.
If I sell all these new parts. THe computer The Harness the sensors intake and TBI and even replace that one bad four wire plug for ignition module... I can recoup a few dollars. Whether stock or modified these trucks if solid inside and out and mechanically sound which mine will be are going over 20k easily if you have receipts and MAN DO I HAVE RECEIPTS.
NOPE not slinging dung against the wall on this. If the engine had not have checked out good and had it not run good going down road initially after the pickup coil replaced minus the idle issue....it ran strong as if new.....I would have opted for the 6200 dollar fully dressed with accessories ENGINE from GM performance. It would have been the 350/290 HP but even that is overkill for me. I don't want a race truck. Just a nice solid driver. I will get it there.
All the help I have gotten is great. It pointed me in the right directions at times. THen if I need further help I use that to pull something up on Youtube to see how its done. Combined it has helped me knock rust off of working on these things. Basics fuel air and spark. Yes I think the 700 was a waste....or is it the parts now....in the long run I can sell some of them for cheap and return some of my money to my pocket. I will have a good running truck before this is over because I am taking my time and addressing other issues I found from the previous owner.
 

RecklessWOT

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I don't hate TBI as a rule. This truck though will never see one again. I spent 700 at least in trying to make it work with new parts. Then took to shop and let him put on laptop. Found bad pickup coil. Replaced. Still dying one minute at stop light low idle next minute on restart idle at 2500. Never went down. Two IAC's two Temps two ign modules O2 sensor TPS new Map New Rebuilt regulator in TBI and new injectors.
At some point you cut bait.
Not a debate but a carb will not kill performance and it takes it back to basics of fuel air and spark.

Few years back I was beating my head against the wall, at about the same point as you (but obviously stopped WAYYY before I dumped $700 into throwing parts at it, that's friggin nuts man) ready to just say screw it and swap to a carb when people on here talked me out of it (and thankfully so, EFI on a daily driver is so much more convenient). Ended up being a bad ECU. Before I knew for sure, just or the heck of it a friend from work who had just dropped a crate motor in his '87 gave me his old computer for free to see if it made a difference and just like that the truck was back to normal. Even if I didn't get it for free, those things are cheap and plentiful at junkyards even if you live in an area that doesn't have a lot of squares in junkyards. Those computers were used in everything. Hell it doesn't even have to be the correct one, the one I'm running from my friend is from a C10 with a 305, my 'burb has a 350 and it still goes vroom just fine
 

eric 87

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Few years back I was beating my head against the wall, at about the same point as you (but obviously stopped WAYYY before I dumped $700 into throwing parts at it, that's friggin nuts man) ready to just say screw it and swap to a carb when people on here talked me out of it (and thankfully so, EFI on a daily driver is so much more convenient). Ended up being a bad ECU. Before I knew for sure, just or the heck of it a friend from work who had just dropped a crate motor in his '87 gave me his old computer for free to see if it made a difference and just like that the truck was back to normal. Even if I didn't get it for free, those things are cheap and plentiful at junkyards even if you live in an area that doesn't have a lot of squares in junkyards. Those computers were used in everything. Hell it doesn't even have to be the correct one, the one I'm running from my friend is from a C10 with a 305, my 'burb has a 350 and it still goes vroom just fine
Part of the FRIGGIN NUTS 700 was a new ECM. New ECM MAP SENSOR TPS (2) IAC (2) Temp sensors , O2 sensor. Nothing helped. Took to shop. He found bad pickup coil so put in NEW complete distributor he said he had for a small block on his shelf and sold me cheap as in 50$ but also rebuilt the TBI and regulator. Seemed fixed. Then the idle acted up again and threw code 42. He showed me the pickup coil though and it was toast.
SO in chasing the new code 42 being ignition module open or short of fuel relay circuit open or short. I replaced both items even though the ignition module in new distributor was new. His labor was factored in as well. He did good as always. Talking me out of the entire engine swap. Which I am not ruling out at this point. We will see.
I have had more TBI and other injections my last a 5.3 LS. But I have had my share of carbs over the years and have never had issues. My 69 firebird of course is stock and with a carb fires up pretty easy unless it sits for a week. Not typical but does happen.
Everyone on here talks about scrap yards for parts. None near me unless there are unknowns in the country are all 2005 and up if not 2010. Anything older they scrap to a shredder. Now I am working on the fuel tanks and entire fuel system. I figure when I get it started today if there are no leaks from water at the intake and it runs good I will most likely order two new 85 tanks and senders with no return lines, I will buy a complete new harness from nose to tail EVENTUALLY and if it we like it after 6 months I may go ahead and order a long block and these parts can swap over on it. At least by then all the sub systems are going to be in place and done. This will be a brand new old 87. OR it will be in someone else garage!
It is solid and we both like the truck. Underneath being I have been under it now for a week is solid as a rock as well. Surface rust on the frame but solid other than that. While it will not be off road it will be in fields maybe at times on the property. And while it will be sharp I will not be a show truck owner. I am not a stickler for stock only although my firebird is 95%. I like clean, no ugly nest of wires nice paint although nicks are okay. Will watch what I do but haul as I need. It will be getting a hitch. It is the truck in the picture but without the 20 inch the prev owner had on it. Like riding on bricks. Now it has coopers on stock rally's.
 

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