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

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

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.

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.

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.

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.

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

Mine was car shaking bucking.

R&R... Please elaborate. Was it just cleaning wiring connections? More? This is good info.

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???

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.

The 123 is one of the hugest upgrades that everyone should do. It's not hard to do, and fixes a multitude.

Does the bucking go away under full throttle? Did you check and adjust the fuel pressure after replacing the fuel pump?

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?

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.

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

Is your tps calibrated with an ohm meter?

The car had horrible vapor lock and it was eliminated with a new fuel pump last year, so the change was a while ago. Never stumbled before.

As far as what was done right before: I installed LED lights from Spoke and for a few minutes had the ignition turned on while I was testing it. Maybe I fried my points? But I looked in the distributor and it doesn't look like points, there are two newish wires coming out from a thing where the points used to be (years ago when I did my own tuneups).

I am somewhat lost so I apologize for the murky descriptions.

Paul

I did not check it. However, with the ignition on, when I move the accelerator cable, I hear what must be the 20 clicks, all regularly spaced. Maybe the TPS went out of calibration? Could that be why the car stumbles with or without it?

Hmmm....maybe just install the new TPS, I already have it.

Paul

New or old, TPS’s require calibration. Calibrate the on you gave and see if that changes anything, although I doubt it will.

Sounds like you don’t have points anymore, depending on what they were replaced with, it may be possible to fry them if you leave the ignition on. That said, if they were fried, I would expect the car wouldn’t even start. Someone else can chime in on that.

So... you’ve been offered several suggestions, why not actually try some of them and report back?

Update: spoke with my mechanic, the car has Pertronix ignition, hence the lack of points. My daytime job is interfering with car matters but I will look into this more carefully this week, appreciate all the input.

But I still wonder, if the car runs poorly with the TPS connected AND disconnected, does that eliminate the TPS as a potential cause?

Paul

In reading about the Pertronix, which is what I have, they caution against leaving the ignition on without running the car and this is EXACTLY what I did when I installed my LED rear lights.

So, I'm gonna get a replacement AND if it fixes it, so be it.
And if it doesn't, I'll have a spare!

Will report back...

Paul

Thanks to everyone who chimed in including Mark 914rubber who thought "electrical" and rjames who asked what I did just before this behavior began.

Im also having a bucking issue with a 73 1.7.

Seems to happen the most around 2-3k rpm as well, but it happens lower/higher as well. Seems to happen more often when car is warm, and when driving on rough roads. Drove it from SF to Santa Cruz a week ago and a 3-4 times during ride down hwy1, would start bucking, and then stall out while driving. Pull over 15min while flooded.

If anyone can pinpoint from that im all ears otherwise ill take the advice already listed.

Start a new thread of your own and add more details. (Ex: FI or carbs? When did the issue start happening, etc.) and people will help.

rjames had me thinking...the last thing I did was mess with my wonderful LED taillights, turning the ignition, working the blinker, running back to look.

Turns out I burnt up the Pertronix, put a new one in and...problem solved! Of course, I first had to order the wrong unit, send it back, get the right one, yaddayaddayadda.

Also, Mark 914rubber sent me a PM saying it sounded electrical, that helped as did everyone else who posted.

So, if I want to check the taillights, I will leave the car running or disconnect the ignition at the coil. And I'll probably put a spare Pertronix in my travel tool bag, along with some crimp on wire connectors.

Thanks again, everybody, love this site!

Paul

So one has to wonder if the Pertronix is truly an 'upgrade' with all of this fiasco. Same goes for the LED lights.

LEDs are most certainly an upgrade. I don't think that's even a debate.
Petronix? Dunno....I don't run it so I can't comment.

here is what I posted also on other thread:

here is my experienced with pertronix, bought my 1st 914 75 1.8 FI last 2011. The car last registration was 2003 and been sitting for 8 years as non-op. So 2011 since I bought it, did nothing with the dizzy except just look at the inside and it is clean, so I didn’t bother changing anything except replace spark plugs and wire for the ignition system and fix all fuel lines and installed SS tunnel lines and other needs to be restored since it was a non-op for 8 years.
I was able to drive the car for more than 4 years until the pertronix failed. Installed old contacts points just to test and it did run again. And since I also have a used pertronix from my stash of dizzy, grab that pertronix and installed it and it run well again even not knowing the condition of that pertronix. Sold the car last 2017 with same pertronix. So meaning, as long you have the right or proper installation, pertronix should be better than contact point.

link below is the other thread regarding pertronix.

http://www.914world.com/bbs2/index.php?sho...52909&st=20

I hope this is contributing to the thread and not a hijack.

I was aware of everyone's concerns about leaving the ignition on and damaging the pertronix. I installed a 2 pin weatherpack connector in the distributor wiring. Now I can disconnect the pertronix module from the car any time I need to keep the ignition on for an extended period of time.

Also handy for swapping distributors on the side of the road if necessary.

For visibility the taillights are terrific. And from what I understand it's possible to burn out the standard points with the ignition on as well. The Pertronix is easy to adjust, especially for someone like me with limited mechanical abilities!

Paul

Check the lights with the engine running.

Thanks for being patient with me everybody. I replaced the Pertronix yesterday and all was fine...until today. Stumbling is as bad as it ever was. I'm fixated on disconnecting the TPS to see if it cures the problem but alas, disconnecting the TPS makes it worse. It is hesitating, maybe a bit better with hard acceleration, but irregular especially under 3000 RPM. Not improved by warming up the engine.

I did NOT leave the ignition on so I should not have fried my Pertronix BUT maybe I should go back to points/condenser??

Paul

Did you replace with Ignitor 1 ?,I've never burnt one out but many say the Ignitor 2 has no issue with leaving the ignition on.
You are running the correct coil with your Pertronix right ?,I only use their matching (impedance) coils just to be sure.

Ignitor 2 BUT I am using a Bosch Blue Coil. I've read that people have run blue coils without issue.
And it seemed to run OK yesterday and now is up to the old shenanigans, so I'm not certain if the coil should
be the source.

It definitely seems electrical. There is a test of resistance in the installation manual for the Pertronix that I did not
follow. Maybe I need to revisit my installation. Ugh!

Paul

I've run Bosch blue coils with Ignitor I on two engines,zero issues ,I don't remember the resistance of them but I know there is a difference with Ignitor 2.
Just dug out my instruction sheet for Ignitor 2,noted the following;
minimum voltage 8V,
coil 0.45 ohms or greater,
"Warning DO NOT USE WITH SOLID CORE SPARK PLUG WIRES".
I'am sure you read all that but probably worth doing the voltage test ,oh and the coil I have is Pertronix 0.6ohm which I didn't use as I'am running a matching transformer coil with my Permatune.
Good luck.

Thanks but I think I'm just not having any luck with this gremlin and may seek additional hands on help!

Paul

So I did more checking according to the Ignitor II instruction sheet.

Checked the air gap, it's just under 0.020" and has not changed.
The net resistance of the aluminum Ignitor plate to ground is less than 0.2 ohms.
The voltage test shows 9+ volts, which is more than 8.0V.

All meeting spec.

So, other electrical issues could be...?
What's with the 123 Distributor?

Paul

123 distributor is plug and play. Easy setup. Love mine so far.

123 distributor is plug and play. Easy setup. Love mine so far.

Updated post #1.

Paul

Time for the six conversion

Looking to test MPS according to my post #1. Set the vacuum at 10 for five minutes, held the negative pressure just fine. Now want to check the leads.

"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"

Are these numbered on the MPS? Do I take it out of the car? Is there a diagram of the terminals??

Paul

Vacuum pump test at 15 in. Hg.

Ohm test inner and outer pairs of terminals (its two coils)

Good vacuum and coil tests would be encouraging, but its the calibration that determines the A/F ratio. Has your MPS been previously adjusted?

No previous adjustments...will test tomorrow, thanks Jeff. Will redo the vacuum test but I think it will pass.

Paul

This is key.

if it still has the epoxy filled over it nose ..it hasnt