Delorean starts bucking after hot and going uphill

[stiness]

So we recently took out the Delorean and it started bucking right before getting home up a slightly steep hill. I thought it was a fueling issue because the fuel pump setup was not stock, slightly janky and it was uphill so I recently replaced it with brand new modern pump from DMC. It ran great again for a while right until heading back home with the car.

The car has no hot start issues, no cold start issues, idles great, revs fine. I did notice it still has the original Ducellier 80amp alternator and when idling the voltage gauge drops to 8 until its revved up. Also as a note it happened with the AC on.

I'm going to check voltage running cold/hot, do a smoke test to see if there's any vacuum leaks, check timing and if I can I'll check the dwell for the afr. Does anyone have any other reccomendations of things for me to check while I'm in there or have run into this problem before?

Thanks for the help!

[Bitsyncmaster]

If your voltage is dropping to 8 volts your battery and alternator are the first things I would replace.

[Rich]

I'm mostly with Dave on this.

If your battery is pretty new then you should focus on the alternator. As you probably know the original Ducys were never up to par even when new. The car's worst-case electrical loads are just too high for it which is why the factory quickly moved to the 90A Motorola unit which was a decent solution. Low-VIN cars with Ducys (and w/new batteries) were dying on the road in SoCal during the summer of '81. Maybe they even bucked a bit before they came to a stop?

A real-time system voltage test will be informative. If the voltage stays >12.6V on a long, hot drive with A/C on and not cycling off, fan at speed 3 or 4 and headlights on then you are probably OK but a better alternator won't hurt. Dropping to 8V is bad for fuel pressure but you report that number only at idle. If pressure goes too low the injectors can't inject fuel.

As for other tests skip the smoke test since the car starts and idles well. Vac leaks don't affect the engine too much under load so maybe hold off on that one. Knowing your idle mixture is OK via dwell test doesn't hurt. Ignition timing almost never is off unless somebody has adjusted and locked it down incorrectly.

The car has no hot start issues, no cold start issues, idles great, revs fine. I did notice it still has the original Ducellier 80amp alternator and when idling the voltage gauge drops to 8 until its revved up. Also as a note it happened with the AC on.

I'm going to check voltage running cold/hot, do a smoke test to see if there's any vacuum leaks, check timing and if I can I'll check the dwell for the afr. Does anyone have any other reccomendations of things for me to check while I'm in there or have run into this problem before?

[Michael]

Drive, repeat the problem and test the voltage at the battery, and the fuel pump. If the advice about the battery and alternator lead to no answers,...Shot in the dark, I suspect the RPM relay.

If you have a OE RPM relay, just get one of Dave's units now because you will sooner or later anyway.

[mhanch]

Drive, repeat the problem and test the voltage at the battery, and the fuel pump. If the advice about the battery and alternator lead to no answers,...Shot in the dark, I suspect the RPM relay.

If you have a OE RPM relay, just get one of Dave's units now because you will sooner or later anyway.

This is the way.

[David T]

If the voltage gets too low you would see the symptoms you describe. The ignition system won't operate properly if it doesn't see enough voltage. Figure out why. If the battery is over 5 years old replace it. Have it tested. If it fails, replace it. Next test the charging system. Clean all of the "big" connections and check the tension of the belt. Make sure the alternator light lights up with the ignition on and the motor NOT running. If that doesn't fix it, the alternator is probably bad.

[DMC VIN 6639]

Are you sure your fuel pump pick up is at the bottom of the tank? Is there a baffle?

[stiness]

If your voltage is dropping to 8 volts your battery and alternator are the first things I would replace.

Yea according to the voltage meter on the dash its dropping to 8ish at idle so I'm starting to think something with the electrical.

I'm mostly with Dave on this.

If your battery is pretty new then you should focus on the alternator. As you probably know the original Ducys were never up to par even when new. The car's worst-case electrical loads are just too high for it which is why the factory quickly moved to the 90A Motorola unit which was a decent solution. Low-VIN cars with Ducys (and w/new batteries) were dying on the road in SoCal during the summer of '81. Maybe they even bucked a bit before they came to a stop?

A real-time system voltage test will be informative. If the voltage stays >12.6V on a long, hot drive with A/C on and not cycling off, fan at speed 3 or 4 and headlights on then you are probably OK but a better alternator won't hurt. Dropping to 8V is bad for fuel pressure but you report that number only at idle. If pressure goes too low the injectors can't inject fuel.

As for other tests skip the smoke test since the car starts and idles well. Vac leaks don't affect the engine too much under load so maybe hold off on that one. Knowing your idle mixture is OK via dwell test doesn't hurt. Ignition timing almost never is off unless somebody has adjusted and locked it down incorrectly.

Honestly when its not bucking the car feels good power wise so your probably right with the timing. I've never messed with it and with how it runs I do doubt its off as well. I'll skip the smoke test too then for the time being.

Drive, repeat the problem and test the voltage at the battery, and the fuel pump. If the advice about the battery and alternator lead to no answers,...Shot in the dark, I suspect the RPM relay.

If you have a OE RPM relay, just get one of Dave's units now because you will sooner or later anyway.

Thanks for the tip, i'll take a look into Dave's units, it's the solid state one right?

If the voltage gets too low you would see the symptoms you describe. The ignition system won't operate properly if it doesn't see enough voltage. Figure out why. If the battery is over 5 years old replace it. Have it tested. If it fails, replace it. Next test the charging system. Clean all of the "big" connections and check the tension of the belt. Make sure the alternator light lights up with the ignition on and the motor NOT running. If that doesn't fix it, the alternator is probably bad.

Thats honestly what I was thinking, the way it bucks it feels more like an ignition issue. I'll make sure to go through all the points you've suggested.

Are you sure your fuel pump pick up is at the bottom of the tank? Is there a baffle?

Yea I'm sure its at the bottom of the tank, it's the new updated one from DMC which is a bucketed style pump. The one that was installed previously was similar to a stock one but no baffle and just a sock filter on the end of the pump instead of a feed line to the bottom of the tank. Thats why I changed it because that one wasn't reaching the bottom of the tank and figured the hills were causing starvation issues.



Thanks everyone for all the pointers and help!