Runs great in park and neutral, falls on its face in drive or reverse while stopped

AMC Diplomat

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I'm just trying to keep the 318 alive long enough until I find a 360 that I don't have to drive 6 or 7 hours each way to get. It's started a new thing where it will rev through the ceiling if I floor it in park and neutral, but in drive or reverse with the car stopped it's like it's governed at a set rpm.

If I don't turn the car over, set the parking brake, and then put it in drive and floor it for a couple minutes, it won't run right the rest of the trip. If I don't do this, it'll want to stubble and stall out at red lights. If I put it in gear and floor it for awhile, it goes to maybe 1500 rpm and just stays there with my foot on the floor, but the rest of trip it's drivable.

The only changes this winter were the new cap and rotor and I put a new coolant temp sensor in. The temp gauge still doesn't work though.

I think I'm dealing with some kind of ignition problem and the computer is playing games. I know I've thrown a little money here and there at it to make it run better in the time I've had it (new choke, choke thermostat, fuel pump, computer, pcv, plugs and wires, cap and rotor) but that's been all nickel and dime stuff I bought cheap. I'm not looking to throw a new distributor and carburetor at it if I can avoid it.

I'm hoping there's a sensor I can replace or some kind of trouble shooting I can do and maybe one of the Chrysler computer experts can point me in the right direction.
 

Ark

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The torque converter isn't capable of allowing the engine to rev higher than 1500 in gear and at a stop. IIRC the stall rating on the factory torque converter is something extremely low, like 1500 RPM. That's the maximum slip allowed between the engine RPM and the actual input shaft speed on the transmission.

In park or neutral the gears are disengaged and the input shaft is allowed to rev freely with engine RPM.
 

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The torque converter isn't capable of allowing the engine to rev higher than 1500 in gear and at a stop. IIRC the stall rating on the factory torque converter is something extremely low, like 1500 RPM. That's the maximum slip allowed between the engine RPM and the actual input shaft speed on the transmission.

In park or neutral the gears are disengaged and the input shaft is allowed to rev freely with engine RPM.
Soooo it suddenly started behaving normally? Jesus what a piece of crap! I'm still curious as to why it won't want to run in drive stopped at light unless I've floored it for awhile first. Bad carb or bad torque converter?
 

69-

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Don't do stall testing all the time. Your trans is easily toasted by flooring without movement. Temperature is getting sick inside trans. What's your trans oil color and odor already? (See and smell dipstick of trans)
 

Ark

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Soooo it suddenly started behaving normally? Jesus what a piece of crap! I'm still curious as to why it won't want to run in drive stopped at light unless I've floored it for awhile first. Bad carb or bad torque converter?
Sounds like an idle problem to me. Unlikely to be ignition unless it consistently misses or runs rough. Sounds more temperature and carb related.

You should stop trying to rev the piss out of it with your foot on the brake, you will eventually overheat and trash your torque converter doing that. It is...concerning that you are dumping heat into everything with no functioning temp gauge while doing this.

I never did much in depth diag on my lean burn system before I removed it. Do you have a service manual with wiring diagrams for your car? Engine coolant temp is one of the inputs for the computer, but I don't know if that sensor drives both the computer and the dash gauge or if they're separate. Not having that input correct will make the computer do screwy things with the mix and the idle. Warming it up fully with the choke open may be getting the mix closer to where it needs to be than whatever you're getting at startup. Unfortunately with no scan tools it is a guessing game as to what signals may be the problem.

General diagnosis process for computer controlled stuff is confirming power, ground, functional and correct inputs, and outputs being actuated correctly. Highly recommend a service manual if you seriously want to try to diagnose and fix this system.
 

Remow2112

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If you think you have an ignition issue buy a non lean burn distributor and slap it in there. It will work on the 360 too. Disconnect the lean burn and set the timing at 10 degrees BTDC.

Shouldn't take more then an hour to do. That will eliminate the ignition as the problem if it still happens. If it still happen it is most likely in the carb and you have a blocked passage. Have you tried upping the idle to like 1k rpm and see if it will stay running in gear?
 

Mikes5thAve

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There's no reason to be revving it in gear to warm it up or pre drive it. It does sound like some sort of carb or ignition problem when it'll run and rev fine in park but not under load. The other slight possibility is if there's something wrong with the transmission that its putting too much load on it. Mixed with other issues I don't know what it'll do for example if lockup is stuck on, if doesn't deactivate it'll cause a hesitation while you're already at speed but not sure what it would do just starting off.
 

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Sounds like an idle problem to me. Unlikely to be ignition unless it consistently misses or runs rough. Sounds more temperature and carb related.

You should stop trying to rev the piss out of it with your foot on the brake, you will eventually overheat and trash your torque converter doing that. It is...concerning that you are dumping heat into everything with no functioning temp gauge while doing this.

I never did much in depth diag on my lean burn system before I removed it. Do you have a service manual with wiring diagrams for your car? Engine coolant temp is one of the inputs for the computer, but I don't know if that sensor drives both the computer and the dash gauge or if they're separate. Not having that input correct will make the computer do screwy things with the mix and the idle. Warming it up fully with the choke open may be getting the mix closer to where it needs to be than whatever you're getting at startup. Unfortunately with no scan tools it is a guessing game as to what signals may be the problem.

General diagnosis process for computer controlled stuff is confirming power, ground, functional and correct inputs, and outputs being actuated correctly. Highly recommend a service manual if you seriously want to try to diagnose and fix this system.
I have a service manual collection. I'm not concerned about trashing anything. It's all original, well over 200k at this point, and poorly maintained by previous owners. I bought the car because it's rust free.

Being nice to it is like trying to fix a rotted beam by painting it. The solution is replacement. If there's an under $50 sensor or wiring fix I'm all for it. I'm more concerned that it is suddenly is working "right" after not behaving like this before.
Don't do stall testing all the time. Your trans is easily toasted by flooring without movement. Temperature is getting sick inside trans. What's your trans oil color and odor already? (See and smell dipstick of trans)
It was jet black when I bought it and after I dumped the pan it's stayed dirty. It's a shit box.
 

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There's no reason to be revving it in gear to warm it up or pre drive it. It does sound like some sort of carb or ignition problem when it'll run and rev fine in park but not under load. The other slight possibility is if there's something wrong with the transmission that its putting too much load on it. Mixed with other issues I don't know what it'll do for example if lockup is stuck on, if doesn't deactivate it'll cause a hesitation while you're already at speed but not sure what it would do just starting off.
Ok. So it's junk. I'll start saving pennies
 

Ark

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I have a service manual collection. I'm not concerned about trashing anything. It's all original, well over 200k at this point, and poorly maintained by previous owners. I bought the car because it's rust free.

Being nice to it is like trying to fix a rotted beam by painting it. The solution is replacement. If there's an under $50 sensor or wiring fix I'm all for it. I'm more concerned that it is suddenly is working "right" after not behaving like this before.

It was jet black when I bought it and after I dumped the pan it's stayed dirty. It's a shit box.
If you're plotting a powertrain swap it's probably not worth throwing time and parts at. You won't be running lean burn on a 360 so it might be worth going to whatever new ignition system and 4bbl fuel pattern you plan to use on the new motor. If it works better, great, if not you're spending that money later anyway.
 

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If the computer fails to advance the timing (transducer failure), it will limit total timing to whatever factory mechanical advance is. Definitely won't run right. But if the TC isn't unlocking, it will act like it wants to stall.

It may be worn out, but there's no reason to beat on it. That never corrects anything.

Side note: I did run a 360 Magnum with Lean Burn in a squad that I had. I simply swapped out the jets and metering rods from a 360 Qjet that I had. Worked perfectly, but the squads had a computer with a very conservative timing advance curve, compared to the 2bbl cars. In those days, the Mopar ignition kit had crazy fast vacuum advance, so we had to play with the springs a bit. Then we had a problem with spark acatter. Eventually I got a new distributor (I think I ordered it for an '88 Ramcharger 360). Funny thing about that set-up: when I went to electronic ignition, I had purchased one of the last new Edelbrock 1905 Quadrajet carbs. I also had an NOS Thermoquad 9387. It was laughably quick with the 1905. Then I put the 9387 on it, and it barked from 1-2, and 2-3. It also pulled right up to the end of the numbers on the speedo, and held right there, no problem. When I sold that car to a collector, he called me when he got home with it, he laughed - "That thing is SCARY fast !!!" .
 
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