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| Need carb education please fellas..... https://www.slantsix.org/forum/viewtopic.php?f=19&t=61546 |
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| Author: | e50095 [ Sat Aug 26, 2017 10:38 am ] |
| Post subject: | Need carb education please fellas..... |
Bought an '87 D100 for cheap with a bad transmission, which I replaced. Now I'm turning my attention to the motor, which does not idle well. It starts quickly and runs good for a few seconds, then starts to miss. I put new plugs, wires, cap, and PCV valve on it, with only a slight improvement. I did a compression check, and every cylinder has between 120 and 130psi. It appears to be running way too rich, my new plugs were soiled only after an hour or so of driving. I tried to research, and one of the things I read about was eliminating the OSAC emissions component and running the vacuum line straight to the vacuum advance line on the distributor. Problem is my distributor doesn't have a vacuum advance pod on the side. Also, my carburetor (1945?) has no air/fuel mixture screw, just a metal barrel cap. Can anyone offer any suggestions on what I can do to bypass that OSAC stuff. I still have the distributor and Holley 1920 from my 68 valiant in the garage, but I have to believe that would be going backward instead of learning something and fixing this correctly. Any suggestions would be sincerely appreciated. Ken in Shrewsbury, PA |
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| Author: | Reed [ Sat Aug 26, 2017 11:25 am ] |
| Post subject: | |
The OSAC isn't your problem, the Lean Burn system likely is. Your 1987 truck will be equipped with a computer controlled distributor and carburetor. This system was used by Chrysler in varying forms in the 1970s and 1980s. it is an early form of computer control and was known to be problematic even when new. Common symptoms of a failed or failing lean burn system are poor idle quality, poor fuel economy, and poor performance. It is virtually universally recommended to remove the lean burn system and replace it with a non-computer controlled electronic ignition system and carburetor. The simplest ignition system to retrofit is the HEI system described HERE Click on the red text. However, that link describes installing HEI on a non-lean-burn vehicle. It is actually easier to install lHEI on a lean burn vehicle than a non-lena burn vehicle. If you decide to pursue HEI, let me know and I can tell you how to do the wiring. You will be ahead in time and frustration if you buy a NOS electronic ignition distributor or a used non-remanufactured electronic ignition distributor. Parts store distributors are very hit-or-miss in quality control, and mostly miss. Try and get a distributor specifically for a truck or van so the timing advance and vacuum advance curves are close to what you need for optimal engine performance. NOS parts vendors such as Old Car parts Northwest should be able to supply you with a distributor. however, you will likely need to get a specific part number for the distributor you want. The same advice goes for the carburetor. The closest match for a non-computer controlled carburetor or your truck would be an early 80s truck or van with a Holley 1945 carburetor. However, older Holley 1945 or Holley 1920s can be made to work with more effort. Try and get a NOS unit or an original condition, non-rebuilt/remanufactured unit. Finally, if the catalytic converter(s) is/are still present on your truck and if it/they is/are the original converter(s), chances are good that it/they are clogged due to an overly rich fuel mixture causing the catalytic matrix to overheat and melt. Replace it/them with new high flow three-way converter(s). Switching to a standard electornic ignition and non-computer controlled carb and replacing the catalytic converter on your truck will likely improve the power, economy, and performance of your truck. Inthe short run, it is worth noting that many lean burn systems often have mis- or disconnected vacuum hoses and electrical connectors. Most people don't know how to properly maintain a lean-burn system and end up disconnecting critcal sensors or vacuum hoses. You might be able to get your current carb and ignition system functioning properly again y getting a factory service manual for your truck and carefully reading and following the diagnosis and repair sections for the lean-burn system. Good luck! |
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| Author: | e50095 [ Sat Aug 26, 2017 11:46 am ] |
| Post subject: | |
Reed, thanks so much for your help. If it was a lean burn system, it wont be worth trying to resurrect. The air cleaner that had the computer attached to it is long gone. Mine has a regular 1 barrel air cleaner with only a breather tube and 1 small vacuum line underneath. I'm gonna do an inch by inch assessment of the motor before starting to collect the parts for an HEI conversion. I have beds and furniture to move so I can't park it until I get all the HEI parts. I've never seen so many vacuum lines in my life, the brain center appearing to be the vacuum amplifier. Never saw one of those on any of my 60's slants. I've already pulled the old catalytic converter off (leaking) and have a new one to put on when the time is right. Thanks again for your help... Ken in Pa. |
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| Author: | Reed [ Sat Aug 26, 2017 12:28 pm ] |
| Post subject: | |
On trucks the air cleaner was usually installed un the inner fender underneath the battery tray. You might very well still have the lean burn computer. If that is the case, you might be able to get it working better by comparing the vacuum hoses on the engine to the vacuum hose diagram that hopefully is still present on the bottom of the hood or on one of the inner fenders. One absolutely critical hose connection that often get disconnected or installed incorrectly is the vacuum transducer on the lean burn computer. It needs to be hooked up and it needs MANIFOLD vacuum, not ported vacuum like a distributor vacuum advance. It should be hooked up either to a port ont he carb or a te in the choke pulloff vacuum hose to provide the computer with a constant signal of pure manifold vacuum. The transducer controls the timing by sensing the engine load via the vacuum of the engine. however, you may have a failed transducer, in which case the engine would operate in limp-in mode. Tracing the vacuum hoses and wiring on the engine is a very good idea and should be where you start. A factory service manual for your truck will be worth its weight in gold when you start tracing hoses and wires. |
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| Author: | e50095 [ Sat Aug 26, 2017 2:13 pm ] |
| Post subject: | |
Your on the money brother. The computer is present and in the fender well on the drivers side. The vacuum line coming from it snakes around and connects to the intake on a branch of the power brake booster fitting. After going over the motor to the best of my ability, along with a vacuum line diagram, I believe I need to get away from lean burn. The lines are brittle, the ones that are there anyway; and the computer controlled carb has a rebuild tag on it, which a lot of folks say spells trouble. Given the lack of power, it's definitely in limp mode. I checked out a couple videos on conversion to regular electronic ignition and also HEI. The HEI folks seem very happy, but I've always been the guy to see a Dodge Brothers street rod at a show, get all excited, then realize its got a small block Chevy in it, and proceed to puke into the nearest trash can. I'm not sure if I can be one of those guys. Either way, it appears I need a vacuum advance electronic distributor, and a non-computer controlled carb. I'll set about making up my mind for sure and start looking for those. Isn't it strange how just a little progress on something can bring your spirit back. This truck has been making everything difficult since I pulled it home, and at 52 changing the transmission on the ground in the driveway with a floor jack was much more physically taxing than I remember from when I was 22. Once or twice I wanted to cry and push it into a lake, but now at least I feel like I have some direction. Thanks again for your help Reed......I can't tell you how much I appreciate it... Ken in PA. |
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| Author: | Reed [ Sat Aug 26, 2017 2:51 pm ] |
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I was actually one of the first guys who years ago tried the conversion from standard Mopar electronic ignition to the HEI unit. This was back before the aftermarket started maing those hideously ugly distributors that were a Mopar distributor base with a GM distributor head on top. Just remember that when you convert to HEI all you are doing is replacing the Mopar ignition control module with a GM ignition control module. You keep the slant six Mopar electronic ignition distributor. If seeing an HEI module bothers you that much, gut the lean-burn computer box and hide the HEI module in there. HEI is truly superior to Mopar electronic ignition in every way and it is much easier and cheaper to switch to HEI than to Mopar electronic ignition on a lean-burn equipped vehicle. But it is your choice. You can put whatever ignition system you want on there. Just be aware that there are numerous well documents instances of the new Mopar ignition modules failing right out of the box from the parts store. NOS is a better bet, but HEI is cheaper and has better availability. |
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