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> Stumbling 1974 2.0...It's finally fixed. Post 63., Thanks to everyone who weighed in, embarrassing reason posted below...
orthobiz
post Aug 23 2019, 05:54 PM
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9/17/19. My resistance numbers are good, my ability to read said number is bad! Paul

9/16/19 I removed the MPS because I could not be assured I was touching the leads appropriately after removing the plug...and what I found...Post 52

Paul

9/15/19 Another update:

Tested the vacuum on the MPS, it's fine. Am hoping to test electrically according to PBAnders site:

"If the vacuum test is passed, check the coil resistances. The primary coil is measured between terminals 7 and 15 and should measure about 90 ohms. The secondary coil is measured between terminals 8 and 10 and should measure about 350 ohms"

Is there a diagram of the terminals? Do I remove the unit to test it? Damn I'm such a newbie!

Paul

9/14/19 update:

My 1974 2.0 with EFI was running fine. Put in LED taillights, left the ignition on to test the blinkers and then the car started running poorly. Thought I fried my Pertronix, put a new one in, seemed to run fine for a day and then started running poorly again. I took some video today but it really doesn't show what is happening as felt in the seat of my pants, i.e. it stumbles but doesn't crack heads back and forth. A loss of power, maybe a bit worse when warmed up, mild surging that is disconcerting and annoying to say the least.

I disconnected the TPS and it didn't run any better. I am wondering if the TPS is bad, could the engine run poorly even if it is disconnected. In other words, does that totally rule the TPS out as the problem?

It just has to be something electric, I think. Should I replace the TPS just to see? I can't imagine going back to incandescent lights will help, it's stumbling with or without the LED lights on.

I'd rather not go back to points/condenser...

Sorry I'm so needy but I am puzzled to say the least!

Paul

Older posts follow:

Update on the update: I fried my Pertronix...see below.

Update: it's more like a hesitating stumbling, happening with or without cruising, that is, it also happens under acceleration. Original post follows:

My 1974 2.0 started bucking all of a sudden. Researching on the site, I'm thinking it's the TPS. Looked in George's Tech Tips 700 book and he advised disconnecting the TPS harness to see if the bucking went away.

To cut to the chase, it bucks especially between 2000-3000 RPM whether the TPS is connected or not. Mainly under light load, while driving and maintaining speed.

It seems to do this more when the engine is warming up, rather than when stone cold.

I am wondering if I should just replace the TPS board. Does the persistence of this problem after disconnecting the TPS rule it out as a cause? I don't feel like tearing into this unnecessarily.

It has a new late style fuel pump that is mounted up front last year, eliminating vapor lock. I've read here that low pressure can be the culprit, but would doubt it in my case.

Perhaps the temp change relationship implies a bad CHT sensor?

Any ideas on things I can easily check much appreciated.

Paul
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mepstein
post Aug 23 2019, 06:13 PM
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Check all grounds and the dizzy.
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orthobiz
post Aug 23 2019, 06:23 PM
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QUOTE(mepstein @ Aug 23 2019, 08:13 PM) *

Check all grounds and the dizzy.


What on the distributor? I read in one thread about bad points, another about advance plates, another about trigger points.

Paul
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northern chris
post Aug 23 2019, 06:54 PM
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You can also try disconnecting each injector one at a time, as a bad injector can cause the same symptom. If you pull an injector and there is no change in running you will have a potential culprit I just went through a similar thing and my issue where the injector trigger points. If you unplug the TPS the car will run fine but accelerate very poorly. Cleaning the TPS board may also help.
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Rand
post Aug 23 2019, 07:02 PM
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Not sure about that last comment. One injector? Unplugging the TPS wouldn't fix that. Electrical is instant on/off style. Fuel tends to more wane, not chop.
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mepstein
post Aug 23 2019, 07:03 PM
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QUOTE(orthobiz @ Aug 23 2019, 08:23 PM) *

QUOTE(mepstein @ Aug 23 2019, 08:13 PM) *

Check all grounds and the dizzy.


What on the distributor? I read in one thread about bad points, another about advance plates, another abut trigger points.

Paul

I don’t know what to do but a friend of mine did an R&R on mine when there was a bad stumble and it went away.
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northern chris
post Aug 23 2019, 07:07 PM
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QUOTE(Rand @ Aug 23 2019, 05:02 PM) *

Not sure about that last comment. One injector? No. Electrical is instant on/off style. Fuel tends to more wane, not chop.


You disconnect one injector at a time, an easy way to check if they are working as they should. If an injector is not working you will get bucking.
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Rand
post Aug 23 2019, 07:09 PM
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QUOTE(northern chris @ Aug 23 2019, 05:07 PM) *

QUOTE(Rand @ Aug 23 2019, 05:02 PM) *

Not sure about that last comment. One injector? No. Electrical is instant on/off style. Fuel tends to more wane, not chop.


You disconnect one injector at a time, an easy way to check if they are working as they should. If an injector is not working you will get bucking.

I appreciate your workflow. But, bucking like the OP described would not be caused by one injector.
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Rand
post Aug 23 2019, 07:11 PM
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Is it stumbling some, or is it real bucking as in jerking the car? Semantics always complicate troubleshooting.
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orthobiz
post Aug 23 2019, 07:55 PM
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QUOTE(Rand @ Aug 23 2019, 09:11 PM) *

Is it stumbling some, or is it real bucking as in jerking the car? Semantics always complicate troubleshooting.


Probably more stumbling, definitely not head banging bucking.

Paul
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mepstein
post Aug 23 2019, 08:07 PM
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Mine was car shaking bucking.
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Rand
post Aug 23 2019, 08:21 PM
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QUOTE(mepstein @ Aug 23 2019, 06:07 PM) *

Mine was car shaking bucking.

R&R... Please elaborate. Was it just cleaning wiring connections? More? This is good info. (IMG:style_emoticons/default/beerchug.gif)
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mepstein
post Aug 23 2019, 08:34 PM
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QUOTE(Rand @ Aug 23 2019, 10:21 PM) *

QUOTE(mepstein @ Aug 23 2019, 06:07 PM) *

Mine was car shaking bucking.

R&R... Please elaborate. Was it just cleaning wiring connections? More? This is good info. (IMG:style_emoticons/default/beerchug.gif)

The usual maintenance on a dizzy. I wish I knew what that was. At least he did.
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ironken62
post Aug 25 2019, 06:41 PM
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QUOTE(mepstein @ Aug 23 2019, 08:34 PM) *

QUOTE(Rand @ Aug 23 2019, 10:21 PM) *

QUOTE(mepstein @ Aug 23 2019, 06:07 PM) *

Mine was car shaking bucking.

R&R... Please elaborate. Was it just cleaning wiring connections? More? This is good info. (IMG:style_emoticons/default/beerchug.gif)

The usual maintenance on a dizzy. I wish I knew what that was. At least he did.

My car is doing the exact same stubbing between 2,500 - 2,900 rpm, rus strong before and after when on the throttle. I have checked the all grounds, vacuum hoses, adjusted the valves, replaced the points and set the dwell at 50 and the car is still stubbing. I also just had to replace the fuel pump. What am I missing???
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HansJan
post Aug 25 2019, 08:27 PM
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I had similar issues when coasting around 3,000 rpm.
Replaced the flamethrower distributor with a programmable one from 1-2-3.

Totally fixed this issue for me.
Not saying that’s what’s going on with yours. But it’s something to consider.
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Rand
post Aug 25 2019, 09:25 PM
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The 123 is one of the hugest upgrades that everyone should do. It's not hard to do, and fixes a multitude.
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falcor75
post Aug 25 2019, 09:40 PM
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Does the bucking go away under full throttle? Did you check and adjust the fuel pressure after replacing the fuel pump?
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rjames
post Aug 25 2019, 10:16 PM
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QUOTE
I've read here that low pressure can be the culprit, but would doubt it in my case.


Why? Unless you’ve verified the correct pressure, it’s a possibility.


Did the car ever not exhibit the stumbling behavior? If yes, when did it start, and what was done to the car right before? Did it begin after the fuel pump was moved?
Have you checked for a kinked fuel line?
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porschetub
post Aug 26 2019, 01:19 AM
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Totally check your ignition system before saying you have a fueling issue,start from the start and then move to your current issue after that,seen this SO many times,good luck.
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orthobiz
post Aug 26 2019, 02:28 PM
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Thanks for all the replies. The stumbling occurs under acceleration as well, seems to be getting rapidly worse. My question: it does it with or without the TPS hooked up, so that means the TPS is not the culprit?

I'll investigate further with my limited skills. If it's solved for sure I'll post what happened! Thanks everybody!!

Paul
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