Acceleration Issue

[SShaw]

I have an 81 Automatic and have recently noticed an issue during acceleration from a stop. If I give it a good amount of gas it'll lose power, regain and lose power again. About 3 times before it is ok. So it bucks a little. If I slowly accelerate from a stop it's ok. If I am already moving, say 5mph, and accelerate hard it's ok. Once it's moving it runs great. Just when I hard accelerate from a stop. Any ideas? Thanks!

[DMC-81]

Hi. I wonder if the plunger in the fuel distributor is sticking a little, or perhaps an ignition wire is loose?

[Michael]

A few things come to mind,
Fuel filter
Vacuum leak at or to the advance solenoid , or the solenoid itself
starving fuel pump, maybe due to the pickup hose collapsing at higher loads or a partially cogged pickup screen
Vacuum leak at the air side causing a rich condition under load or a dirty air filter.

[Jonathan]

That sounds to me like either the shift computer on your car is acting up or your auto trans fluid filter is plugged.

Has your shift computer ever been rebuilt? Or inspected recently to see if any of the wires have gotten melted laying too close to the exhaust piping?

When was the last time you changed the transmission filter? Or fluid? The ATF filters Michael helped reproduce are a good product.

[SShaw]

I just replaced all the vacuum hoses yesterday. It was doing it before and still is. So hopefully not a leak. I replaced the air filter in the last couple of weeks. I have a fuel filter on the shelf waiting to be put on.

I've had the car 3 years and haven't done the transmission fluid or filter. They are both on the top of my to do list. I don't know if my shift computer has ever been rebuilt.

[Michael]

I just replaced all the vacuum hoses yesterday. It was doing it before and still is. So hopefully not a leak. I replaced the air filter in the last couple of weeks. I have a fuel filter on the shelf waiting to be put on.

I've had the car 3 years and haven't done the transmission fluid or filter. They are both on the top of my to do list. I don't know if my shift computer has ever been rebuilt.
So is the transmission slipping or is the engine not making power?

[David T]

You must determine if it is an engine problem or a transmission problem. One way to do that is to hook up a light box and verify the shift computer is selecting the appropriate gear for the speed and throttle position. My guess is you are not getting 1st gear all the time so you would not get much acceleration. If the problem seems to improve as the motor warms up, it sounds like the shift computer is not working right when cold but gets better as it warms up. It can also be the motor, some systems function to warm the motor up faster and when they don't work or work right the motor won't feel right until it is fully warmed up. Verify the transmission is actually being commanded into 1st gear at a standing start when you notice the lack of acceleration.

[SShaw]

So is the transmission slipping or is the engine not making power?

I believe the engine is not making power. But I could be wrong.

[SShaw]

You must determine if it is an engine problem or a transmission problem. One way to do that is to hook up a light box and verify the shift computer is selecting the appropriate gear for the speed and throttle position. My guess is you are not getting 1st gear all the time so you would not get much acceleration. If the problem seems to improve as the motor warms up, it sounds like the shift computer is not working right when cold but gets better as it warms up. It can also be the motor, some systems function to warm the motor up faster and when they don't work or work right the motor won't feel right until it is fully warmed up. Verify the transmission is actually being commanded into 1st gear at a standing start when you notice the lack of acceleration.

This is helpful, thanks. Is there place that has information on using a light box? I'm not familiar with that.

[Jonathan]

I believe the engine is not making power. But I could be wrong.

When you have this loss of power event upon taking off from a stand still, what do the engine RPMs do?

Meaning, when you give it gas to get going, do the RPMs rev high and yet you aren't getting anywhere yet? Or do they stay pretty low even though your foot is pressing on the gas and the car should be picking up speed?

I have had experiences on my own car like this. It was two different things though. The plugged trans filter was starving the transmission of fluid and so even though I was giving it lots of gas, it just had no oomph and wouldn't go anywhere. The RPMs went way up in this case. I would shut the car off (which I think would let the plugged filter relax momentarily and allow some fluid by) and then when I turned it on again, I got going for at least another few blocks. I changed the filter and this never happened again.

Years before that though, and before I did any work on the shift computer, it was changing gears erratically. I later realized one of the governor leads was melted after laying on top of the exhaust crossover pipe. A test you can do to see if the computer is at fault or not, is to pull the fuse for the shift computer and see how it behaves. The default gear when there is no electrical power to the shift computer is supposed to be 3rd gear. What it feels like when you only have the 3rd and final gear in a DeLorean, is that the car will have no power leaving from a stand still. The car will eventually be okay once you creep up to highway speeds, but will feel like there is next to no power while driving at low speeds in that 3rd gear. Don't drive it like this any longer than you need to to confirm where there problem is. Good troubleshooting test though and easy to do.

[SShaw]

When you have this loss of power event upon taking off from a stand still, what do the engine RPMs do?

Meaning, when you give it gas to get going, do the RPMs rev high and yet you aren't getting anywhere yet? Or do they stay pretty low even though your foot is pressing on the gas and the car should be picking up speed?

I have had experiences on my own car like this. It was two different things though. The plugged trans filter was starving the transmission of fluid and so even though I was giving it lots of gas, it just had no oomph and wouldn't go anywhere. The RPMs went way up in this case. I would shut the car off (which I think would let the plugged filter relax momentarily and allow some fluid by) and then when I turned it on again, I got going for at least another few blocks. I changed the filter and this never happened again.

Years before that though, and before I did any work on the shift computer, it was changing gears erratically. I later realized one of the governor leads was melted after laying on top of the exhaust crossover pipe. A test you can do to see if the computer is at fault or not, is to pull the fuse for the shift computer and see how it behaves. The default gear when there is no electrical power to the shift computer is supposed to be 3rd gear. What it feels like when you only have the 3rd and final gear in a DeLorean, is that the car will have no power leaving from a stand still. The car will eventually be okay once you creep up to highway speeds, but will feel like there is next to no power while driving at low speeds in that 3rd gear. Don't drive it like this any longer than you need to to confirm where there problem is. Good troubleshooting test though and easy to do.

Thanks! Good call on the RPMs. I’ll take a look at that next time I’m out.

[SShaw]

Here is a video. It is dropping RPMs a bit. Sorry it's so shaky, I got on the gas pretty good and it was bucking a lot.


https://www.youtube.com/watch?v=5NOJZKHP5f0

[Michael]

Here is a video. It is dropping RPMs a bit. Sorry it's so shaky, I got on the gas pretty good and it was bucking a lot.


https://www.youtube.com/watch?v=5NOJZKHP5f0

Probably need to see the speedo too. If the car feels like it stops pulling as the rpm climbs then I would say the trans is slipping but they generally don't catch themselves like that. Doesn't look like it's starting in second gear either.

[SShaw]

Probably need to see the speedo too. If the car feels like it stops pulling as the rpm climbs then I would say the trans is slipping but they generally don't catch themselves like that. Doesn't look like it's starting in second gear either.

I’ll try to do one with the speedo tomorrow. I don’t think it’s starting in 2nd. It smoothly shifts to 2nd at the end of the video.

[Ron]

It don't seem like the trans from the video to me.

Have you check your timing and/or fuel pressures?

[SShaw]

It don't seem like the trans from the video to me.

Have you check your timing and/or fuel pressures?

I have not checked those things.

Here are two more videos with the speedometer. One is from a stop with the issue. One is from a slow speed without the issue.


https://www.youtube.com/watch?v=aREhe31HtMQ&list=WL&t=0s&index=10

[SShaw]

From Stopped.


https://www.youtube.com/watch?v=AvcxccW58b8&list=WL&index=10

[Jonathan]

I don't know what exactly is going on, but I would not want to drive that car much more like it is. Start doing diagnostics in the garage with it parked. Continuing to put the transmission through that sort of thing could presumably cause more damage than there is already.

There are a series of checks to do on the auto trans that would be a good idea for you right now. It's in the shop manual. Go through all of those things along with visual inspections of the shift computer harness. Check the fluid, change it, inspect and / or change the filter.

Park the car until you know more about what it isn't by going through the suggestions in this thread already made for you.

[Elvis]

Somehow it feels like wrong shifting to me, too.

LEDs on the governors output to see the selected gear would be great.

[Ron]

In the "From Stopped" vid, it seems to me that the GC isn't calling for a shift because the RPM isn't reaching the level required for the accelerator position, until it finally works its way up and shifts. IE It doesn't sound like the surging is caused by shifting or slipping, but bogging (in the ~3000 RMP range, each gear).

Could be my old ears ;-)

Just in case:

Is there place that has information on using a light box? I'm not familiar with that.
http://dmctalk.org/showt e be mhread.php?350-Automatic-Transmission-Governor&p=26804&viewfull=1#post26804 (http://dmctalk.org/showthread.php?350-Automatic-Transmission-Governor&p=26804&viewfull=1#post26804)
Gear..L1....L2
1.......On...On
2.......On...Off
3.......Off...Off

[dmcnc]

My first question would be, did you do anything to the car before the symptom showed up?

Second, it does seem like a transmission issue. There are a lot of simple things you can check before going down the rabbit hole like, have you checked your trans fluid levels?

Make sure to check the governor control cable adjustment (Workshop Manual G:05:02). It’s an easy thing to check, and your shifting will be off if incorrectly adjusted. (Probably on all gears though).

After that I would check transmission wiring for any signs of burning or melting, followed by verifying vacuum connections to the transmission.

[Ron]

It would be interesting to see what it does if you lock it into 1st and let it wind up to ~3000 RPM then hold it there a few seconds...

[SShaw]

Thanks everyone. Work just got really busy so I haven’t had time to look into it. I’m hoping to spend the 14th on it. I have a fuel filter, transmission filter and pan gasket on the way. I’ll visually inspect the governor while I’m working on those. Thanks again!

[SShaw]

I just changed the transmission fluid and replaced the transmission filter. The problem has been resolved. Thanks everyone!

[Jonathan]

That sounds to me like either the shift computer on your car is acting up or your auto trans fluid filter is plugged.

Has your shift computer ever been rebuilt? Or inspected recently to see if any of the wires have gotten melted laying too close to the exhaust piping?

When was the last time you changed the transmission filter? Or fluid? The ATF filters Michael helped reproduce are a good product.


I just changed the transmission fluid and replaced the transmission filter. The problem has been resolved. Thanks everyone!

Whoo hoo!! We have a winner! 10 Internet points for moi, your one and only resident DeLorean guru.

Humbly yours,

The Fixer

hahahahaha!!!

j/k ...glad to hear you got it all sorted out.

[Michael]

I just changed the transmission fluid and replaced the transmission filter. The problem has been resolved. Thanks everyone!


I would LOVE to see a pic of the old filter

[David T]

I would LOVE to see a pic of the old filter


It would have to be a picture of it cut open to see anything. If the filter was plugged up enough to mess up the shifting you have to worry about how much friction materiel is left on the discs. While the problem may seem to be solved, it remains to be seen if it starts slipping soon. The line pressure should be checked and a picture of the pan before you cleaned it would be useful too. Was there any metal in the pan and if so, how much? BTW, I was the first to raise the possibility of the transmission as the source of the problem. Sometimes you get a lucky guess. The main thing here is the wide ranging amount of brainpower and experience that we can bring on a problem and help get it resolved. I ask for no credit and am happy we got another Delorean going again.

[DMC-81]

It would have to be a picture of it cut open to see anything. If the filter was plugged up enough to mess up the shifting you have to worry about how much friction materiel is left on the discs. While the problem may seem to be solved, it remains to be seen if it starts slipping soon. The line pressure should be checked and a picture of the pan before you cleaned it would be useful too. Was there any metal in the pan and if so, how much? BTW, I was the first to raise the possibility of the transmission as the source of the problem. Sometimes you get a lucky guess. The main thing here is the wide ranging amount of brainpower and experience that we can bring on a problem and help get it resolved. I ask for no credit and am happy we got another Delorean going again.

Well, Jonathan's post was #4. Your post was #7....not that anyone is counting.

Yes, helping people out is the main reason we are all here, and I'm also glad that the OP solved the problem. It's nice to see the results posted. That helps the entire community with a searchable use case for the problem.

[opethmike]

Well, Jonathan's post was #4. Your post was #7....not that anyone is counting.

Yes, helping people out is the main reason we are all here, and I'm also glad that the OP solved the problem. It's nice to see the results posted. That helps the entire community with a searchable use case for the problem.

Don't argue with him - he has a mustache!

[Michael]

It would have to be a picture of it cut open to see anything.

Which is partially my point guru. People look at the one triangle intake and see clean mesh and assume the filter is clean. I am not in the filter business anymore so I can be unbiased but owners need to know to freaking replace an oe filter no matter how clean it looks. Before new filters were avaliable there was an acceptable excuse to rip them apart and try to clean them and put them back together, now there just isn't.

[Jonathan]

Damn it... keep forgetting where I put that sarcasm font.

[Michael]

Well, Jonathan's post was #4. Your post was #7....not that anyone is counting.

:nutkick:

[SShaw]

It would have to be a picture of it cut open to see anything. If the filter was plugged up enough to mess up the shifting you have to worry about how much friction materiel is left on the discs. While the problem may seem to be solved, it remains to be seen if it starts slipping soon. The line pressure should be checked and a picture of the pan before you cleaned it would be useful too. Was there any metal in the pan and if so, how much? BTW, I was the first to raise the possibility of the transmission as the source of the problem. Sometimes you get a lucky guess. The main thing here is the wide ranging amount of brainpower and experience that we can bring on a problem and help get it resolved. I ask for no credit and am happy we got another Delorean going again.

I didn’t notice any metal in the pan. It was a little sludgy. There was a small magnet on the filter that had some metal on it. I cleaned it and stuck it to the new filter.

[David T]

It is still necessary to cut the filter open to see how much debris is actually inside. I agree it is better to replace than clean but for a long time filters were not available. If there is enough debris inside to plug the filter up there probably is not a lot of life left in the friction discs and a rebuild will be necessary sometime soon. A plugged filter is another after-effect of a bad shift computer or very high mileage. Like the clutch in a 5 speed the friction plates in an automatic transmission wear when you shift. When enough friction materiel comes off the plates will start slipping. A plugged filter lowers the internal line pressure so the plates aren't held together tight enough and that causes slipping and excessive plate wear. The excessive plate wear creates more friction materiel and that just plugs the filter up more. That is why it is important to open the filter and see how much friction materiel is shed and how much metal. Bottom line a plugged filter is not a cause, it is a symptom. If you only fix the symptom you will just get it back again if you do not fix the cause (unless it is just a lot of mileage). The magnet is supposed to sit in the pan on that round bump. If it was not in it's correct position it means you were not the first one inside. Recheck the fluid level after a few miles as per the procedure in the manual. Don't forget to also check the final drive too.

[David T]

It is still necessary to cut the filter open to see how much debris is actually inside. I agree it is better to replace than clean but for a long time filters were not available. If there is enough debris inside to plug the filter up there probably is not a lot of life left in the friction discs and a rebuild will be necessary sometime soon. A plugged filter is another after-effect of a bad shift computer or very high mileage. Like the clutch in a 5 speed the friction plates in an automatic transmission wear when you shift. When enough friction materiel comes off the plates will start slipping. A plugged filter lowers the internal line pressure so the plates aren't held together tight enough and that causes slipping and excessive plate wear. The excessive plate wear creates more friction materiel and that just plugs the filter up more. That is why it is important to open the filter and see how much friction materiel is shed and how much metal. Bottom line a plugged filter is not a cause, it is a symptom. If you only fix the symptom you will just get it back again if you do not fix the cause (unless it is just a lot of mileage). The magnet is supposed to sit in the pan on that round bump. If it was not in it's correct position it means you were not the first one inside. Recheck the fluid level after a few miles as per the procedure in the manual. Don't forget to also check the final drive too.

Ans YES, Jonathon, you did mention the trans filter first. Congratulations. I am happy to see that others are getting good at diagnosing problems too. I will not be here forever so it is good to see that others are getting good at this. Especially the automatic transmission. To many it is a mysterious wet box that when it breaks, costs a lot to fix.

[opethmike]

Do you need a hug, Dave? 'Cause you seem like you could use a hug.