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Old 02-21-2014, 08:15 PM   #1 (permalink)
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Thoughts on replacing Lucas EFI with TBI

Hello all - this is my first post here, so here it goes. An earlier post rather thoroughly discussed ditching the Lucas efi system and replacing it with a carb. Towards the end of the post, it was suggested that maybe pulling the Lucas efi and replacing the system with a throttle body fuel injection system (from either affordable, Howell, etc.)would be the way to go. I had actually been considering the same. My current system in my 1990 3.9L is dying a slow death. Every few months I am chasing down a short to ground or a dead sensor. I completely agree that the Lucas system is simple enough, and when working properly, is much better than the best carb setup I have ever had. Mine is just no longer reliable. So, I completely understand the desire to go carb. I briefly considerd this option, and frankly admire anyone up to the challenge. However, I think the TBI system may be the best of both worlds - simplicity, reliability and new. So, basically I am seriously considering a TBI system, Davis Ignition system and a painless wiring 18 circuit rewire. Since all of the dash indicators are sensors, the speedometer is mechanical, I am thinking that this is doable and would be realitively achievable. I suppose the tach might not work. When completed, thetruck should be simpler, and a bit more reliable for the foreseeable future. Id like to know your thoughts and whether you forsee any difficulties, problems or complications that i am just not seeing. Thanks. Discuss.

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Old 02-21-2014, 10:29 PM   #2 (permalink)
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Sounds like more work and money than fixing the current problems.
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Old 02-22-2014, 08:05 AM   #3 (permalink)
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Yes - it will be a lot of work and money, but a task I am willing to take if it could be done with minimal complications and results in better reliability.
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Old 02-22-2014, 08:22 AM   #4 (permalink)
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Am I thinking this through correctly? I'm thinking that all I would need to do is remove the Intake manifold, and all related Lucas Hotwire wiring and sensors, remove the efi computer, and the fuses related to efi (so the dash warning lights are not constantly flashing), the distributed, coil, and related ignition wiring. Then replace the intake manifold with an edelbrock Buick 215 intake manifold, bolt on the TBI kit, wire in the TBI harness, run a new accelerator cable, install a Davis Unified ignition and then program

I dont see why I couldn't use the existing fuel lines and in tank fuel pump. Yes it is a lot of work, but rather simple work - its mostly the expense and fear of the unknown that is holding me back.
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Old 02-22-2014, 10:27 AM   #5 (permalink)
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I think you will have fueling problems similar to the supercharged p38

At least with a carb you cab overfuel to compensate, not with the o2 sensor

I don't see how the tbi will be more reliable than 14cux. It has 1 less o2 sensor and a map instead of maf. Other than that its very similar. What sensors are you having to replace?
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Old 02-22-2014, 11:55 AM   #6 (permalink)
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I have had to replace - within the past 18 mos - two O2 sensors, stepper motor and I am on my second ECM. Every few months it's something new, hard hot start, iratic idle, stalling or a major drop in mileage. And it always happens at the worst time.

I'm mostly thinking that TBI will be more reliable because everything down to the harness will be brand new.

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Old 02-22-2014, 12:10 PM   #7 (permalink)
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I have had to replace - within the past 18 mos - two O2 sensors, stepper motor and I am on my second ECM. Every few months it's something new, hard hot start, iratic idle, stalling or a major drop in mileage. And it always happens at the worst time.

I'm mostly thinking that TBI will be more reliable because everything down to the harness will be brand new.
The problems you have will likely not be fixed by changing systems.
Idle and stalling are the same problem. Mine currently does this because it's running too rich, but yours might just need the idle reset . For hard hot start check the temperature sender. Buy a rovergauge cable and you can do this easily from a laptop.

New vs old is not your problem. Nor will it be your solution.
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Old 02-22-2014, 12:27 PM   #8 (permalink)
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They both use the same iac, and if you replaced the computer and still have problems it wasn't a bad computer
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Old 02-22-2014, 02:14 PM   #9 (permalink)
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It is running ok....for now.... I was just listing all that I have done to the efi / ignition systems in the past 18 months. I replaced the computer when I was getting spark but no fuel, and the problem was fixed. I'm not trying to fix anything, I'm simply trying to improve reliability.

I really still can't see how a new, simpler system will not be more reliable.

I appreciate all the advice, maybe I will consider sticking with what I have. A few years ago I was going to carb it. Obviously I didn't, but I have done so much work and spent so much time on it that I'm still trying to think of other options. I am fully aware that tinkering and field fixes are part of RRC ownership, but I'd just like to see if I could do something to make it more reliable. The ignition and efi give me the most trouble.

It's a good possibility that I'm just looking for another project to scratch that itch to tinker.
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Old 02-22-2014, 07:46 PM   #10 (permalink)
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8 times out of 10 the Lucas 14cux issues come down to poor sensor quality and age. If the system you use is new and has modern quality sensors I don't see it being any less reliable provided it is installed properly.

Not really sure if is worth the effort though. Time spent sourcing better quality sensors and repairing the wiring harness would probably be better if you want to keep EFI.
The multi port injection found in the stock Lucas injection is superior to a throttle body design anyway.

That's just my 2c. You should try it and let us know how it worked out.
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Old 02-22-2014, 08:07 PM   #11 (permalink)
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Thanks Bridger. I agree, the age of the 14cux is killing me. 24 years of road vibrations and 100 degree Texas heat are slowly killing it.

I also agree that it may not be worth the effort, certainly not the cost, but maybe the effort. If I can get two trouble free years (something lucas has not given me), it will be worth it

If I do this I might start a thread and document my progress.
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Old 02-22-2014, 11:29 PM   #12 (permalink)
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I really still can't see how a new, simpler system will not be more reliable.
How will the new system be simpler?
I can see it being less evolved, but that doesn't make it simpler or having fewer failure points.
You'll still have injectors and fuel lines to fail. But these will now likely include home-made connections.
You'll still have oxygen sensors, also now with home-made connections and home-made wiring harness mountings.
You'll still have an ECU and wiring. But again you'll be making up your own wiring and mounts.

See where I'm going with this? Any new and untested system is a magnitude more unreliable than one that works but has a few age related problems.
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Old 02-23-2014, 07:38 PM   #13 (permalink)
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Thanks for the response Dougal. If there are fewer points, would there not be less prone to failure? Also, it is my understanding that these systems are based off the GM TBIs which in my experience are much more reliable (not better) than Hotwire, and parts are more plentiful and less expensive. Also, why couldn't a properly constructed home-made wiring harness be just as reliable as a oem made and installed system, especially one over 24 years old?

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Old 02-24-2014, 12:37 AM   #14 (permalink)
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Thanks for the response Dougal. If there are fewer points, would there not be less prone to failure? Also, it is my understanding that these systems are based off the GM TBIs which in my experience are much more reliable (not better) than Hotwire, and parts are more plentiful and less expensive. Also, why couldn't a properly constructed home-made wiring harness be just as reliable as a oem made and installed system, especially one over 24 years old?
How well you can do a DIY system comes down to how skilled, talented and careful you are.

But it stands to reason that someone skilled, talented and careful enough to make a DIY system as reliable as an OEM system would have no problem sorting out simple and long term fixes to the existing issues.
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Old 02-24-2014, 07:07 AM   #15 (permalink)
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Do this: Megasquirt for V8 engines - What is Megasquirt all of the work has been done for you. You keep most of the current components and get rid of the bad ones. In addition, you add EDIS.
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Old 02-24-2014, 10:37 AM   #16 (permalink)
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Be aware that the Davis distributor is not a bolt-in for our engines. At the least you will need to cut down one of the manifold bolts to clear. Milling the corner of the intake is a better idea perhaps.

But, why get rid of the distributor you have? It will work fine with whatever EFI you go with.

Similarly, why get rid of the intake you have when it will work fine with any TPI.

Or, better yet, go Mega-Squirt and do away with the distributor other than oil pump drive.

I will be starting on not one but two and maybe three Mega-squirt installs this spring. Really looking forward to it finally!

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Old 02-24-2014, 04:10 PM   #17 (permalink)
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How well you can do a DIY system comes down to how skilled, talented and careful you are.

But it stands to reason that someone skilled, talented and careful enough to make a DIY system as reliable as an OEM system would have no problem sorting out simple and long term fixes to the existing issues.
Bingo


14cux harnesses are pretty modular, grab one from another truck and patch it in if you think there are problems.
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Old 02-24-2014, 04:12 PM   #18 (permalink)
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I will be starting on not one but two and maybe three Mega-squirt installs this spring. Really looking forward to it finally!

Why? 14cux is now tunable if you need it. Are these at least heavily modified engines that you are converting?
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Old 02-24-2014, 04:25 PM   #19 (permalink)
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Why? 14cux is now tunable if you need it. Are these at least heavily modified engines that you are converting?
elaborate please...
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Old 02-24-2014, 04:42 PM   #20 (permalink)
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Start here

http://www.pistonheads.com/gassing/t...th%2C+Chimaera

cliff notes:

most of the important memory locations have been identified and a decent understanding of what they do exists. A .xdf for Tunerpro exists that autocalculates checksum.

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Old 02-24-2014, 08:14 PM   #21 (permalink)
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Start here

Instructions to change fuel maps on 14CUX Griffith, Chimaera - PistonHeads

cliff notes:

most of the important memory locations have been identified and a decent understanding of what they do exists. A .xdf for Tunerpro exists that autocalculates checksum.
I've got everything to do it. Just getting down the list. I'd need some petrol in it first.
The fuel map is a nice table of 144 cells. Rovergauge shows you exactly which one you're currently in, a wide-band A/F gauge shows you where you're currently running.
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Old 02-25-2014, 06:53 AM   #22 (permalink)
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Why? 14cux is now tunable if you need it. Are these at least heavily modified engines that you are converting?
It is, somewhat... But the MS allows you to adjust and control everything and easily put on EDIS as well, getting rid of another crappy system. You also lose the expensive and finicky old school mass air flow meter. You can tune properly with a wide band sensor and get everything really well setup.
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Old 02-25-2014, 08:12 AM   #23 (permalink)
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It is, somewhat... But the MS allows you to adjust and control everything and easily put on EDIS as well, getting rid of another crappy system. You also lose the expensive and finicky old school mass air flow meter. You can tune properly with a wide band sensor and get everything really well setup.
I'm very familiar with it, but if you think its more reliable than 14cux you are mistaken.
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Old 02-25-2014, 06:32 PM   #24 (permalink)
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Ok -so the overwhelming majority fell that a 24 year old 14cux system is very reliable, even more so than a new Tbi system. I am open to the possibility that my system is just possessed.
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Old 02-25-2014, 09:01 PM   #25 (permalink)
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No, there is a five man strong 14Cux fan club on Pirate who insist it's the dog's bollocks because its basic enough to mess with and are under the impression it will never cause any problems as long as you are smart enough to constantly repair it.

Truth is 14cux was already obsolete before it was even introduced and age hasn't improved it any.

Can the stock 14cux be reliable? Of course, and it is much better than the Lucas EFI systems that came before it but these days there are other options. Especially for EFI.
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