WoodsRunner88

Sorry for the long description, I am trying to get as many details in so it is more clear of what is going on so folks can have an easier time trying to help.

My buddy highluxurynineteen8E has a 1980 20R Longbed 2WD with a factory 3 speed automatic. The truck has had distributor issues in the past. When he first acquired it, it had a stumble issue when you went from a stand still idling and started to accelerate. It would have a power lag for a second then compose itself and take off like normal. I fussed with it and found out that the signal module in the distributor was sticking. So I cleaned everything up, and also routed the two lines going to the distributor correctly. After that it drove like an EFI truck, smooth as silk. A month or so later it started to do it again so we decided to put a new distributor and advance diaphragm combo from rock auto on it. Got the distributor, put it in and put all the new stuff back on it: cap, rotor, wires, coil, and plugs along with new vacuum lines, and the truck ran like a new machine, started nice, no problems for more than a month up until a couple weeks ago.

I will best describe what the truck is doing now. It seems to be way advanced now at certain times. First I checked the idle speed and ignition timing at idle after it was at running temp for 20 minutes or so and ashort drive. I disconnected the vacuum hose that is closest to the distributor, the one that does not have the VTV on it, and the idle dropped and I set the timing and the idle speed was around 900 or so, and it ran smooth. I then replugged the hose to the distributor, and it took a second but the idle went up to 1100 there abouts and I saw the timing advanced when I used my timing light. I set it to 8 BTDC like it wanted (I can’t remember the exact number) in the engine FSM. I turned the idle down also to around 900 rpm plugged in. Now I don’t remember the timing advancing like that when I used to plug in the old distributor, it never changed no matter what you did. So with everything set to factory specs I took it for a drive.

From a stand still on a long hill I pushed the throttle to half way, and held it there, it smoothly shifted to second then to third at about 40 mph, but right after it shifted it stopped accelerating and began to ping, then shutter, then backfire out of the intake. Now I tried different things to try to correct it like fluctuating the throttle, that didn’t help, then I let off completely and then slowly got back into it but at as soon as a drag was put on the engine it would go through it’s sequence of events (the whole sequence from pinging to backfire takes between 2 to 4 seconds). I then tried matting it and that didn’t help, nothing I did could stop it shuttering, even when I would shift it to 2nd to bring the revs up it would keep shuttering and backfiring. So I pulled over after trying everything from the driver’s seat. I disconnected both lines to the distributor and plugged them and drove it. It had a slight lag off the get go, but once I was rolling it was smooth as silk, just very slow with no power, but I could never get it to ping, shutter or anything even up around highway speeds, which is where it shutters the worst at anything 40 mph and up. So I reconnected the two lines, and retarded the distributor (after marking it’s correct location for later)as far as it would go, and tried it but it would still when it hit 3rd or even high in revs in second would ping, shutter and backfire. I returned the distributor to it’s previous position, keeping the lines connected and nothing changed. I then drove it and as soon as it would shutter I would immediately pull off the road and pull the lines off the distributor, the engine would slow down, and then I would reconnect them, the engine speed would go back up, after this the truck would easily get up to speed and stay composed for about 3 to 4 minutes then it would shutter again as soon as demand was put on the engine. I pulled the cap off and the signal module moved freely when I sucked on the vacuum line, and return back as far as it could, even with the other line on (engine was not running). I then checked and saw that with the lines disconnected at idle the one vacuum line that is closest to the distributor would have high vacuum, but as I raised the engine speed to 2000 rpm and higher then the one with the VTV would have higher vacuum, and the other would have no vacuum that could be felt. Everything seems fine up to the distributor, but I believe it has something to do with a faulty diaphragm in the advance. It is frustrating cause my buddy drives the truck daily and needs it, and I am at college and only can look at it when I am home once a month. So please any ideas would be great.

Thanks,
Chris Y.

Thelast83inNJ

If you think or know that the vacuum application to the new distributor is routed and working correctly, (I'm not there nor do I know how it works stock anymore) maybe the ignitor is loosing it's mind scattering the spark signal or maybe the distributor shaft is wasted (play). Shove the old distributor back it since you said the old didn't misfire or ping. Just because the part is new doesn't mean anything today.

83Toyota88

iTrader: (1)

Step 1 to me would be to get a vacuum gauge tester and test both side of the advance diaphragm and make sure it hold vacuum. Or you could suck on the tubes and see if it holds position or moves.

If it seems to hold vacuum then your problem is on the other end of the vacuum lines that actually applies the vacuum to advance the distributor. Try to get your friend to post a picture of where the advance lines are running too so we can double check they are hooked up.

WoodsRunner88

Thanks guys for the responses I believe I will got and get a vacuum tester or make one, and will try that, and you are definitely write about "new junk" now, you just never know. I can get him to get a picture but I used a vacuum diagram that was in a Haynes manual, it was for a federal 1980 and all of the lines were routed correctly, and I matched the lines to the diagram and they agreed with the manual. I will let him know.

Thanks again guys!