Cutting Out, Bad miss- Help Needed Options

[PDXBob]

Frustrated by a Bad Miss. hope the 914World Experts can help me out!

On my 1975 914 (1.8) I have had a sporadic bad miss for the last 6 to 8 months. Here are some of the details.

- it’s been doing this for at least 6-8 months. Some days doesn’t miss at all. But today it was bucking so hard I didn’t know if I’d make it home. This was the worst it’s ever been!

- When it misses it feels like it’s bucking, that is, doesn’t feel like one cylinder miss but total cut out.

- it’s worse under a load, e.g. when going up a steep hill.

- In the driveway today I could rev it up and hold it while standing still with no miss. Didn’t matter if I held it at 2,000, 3,000 revs- didn’t miss.

- not sure if fuel or electric issue. Any tests I could do to determine?

- Does it in all gears.

- The Tac does NOT fluctuate when it cuts out.

- The lights and radio do NOT flicker or stop.


Any suggestions would be greatly appreciated. Thanks in Advance!
PDXBob

[rjames]

When was the last time you overhauled your distributor?

[Olympic 914]

I had a similar issue coming back from Okteenerfest.
It began during the drive while there,and continued during the drive home.
With 200+ miles to go and the missing getting worse, I started pulling plug wires and had a questionable spark on #3
Ultimately I found a Flaps and bought new spark plugs.
The ones I took out did not look THAT bad.
But have not had an issue since changing the plugs.

Might be worth a try.

Do the simple stuff first.

[technicalninja]

(IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif)

Especially if you don't know how long it's been since stuffs been changed.

The basics are:
Ignition:
Points and condenser. Set timing and dwell.
Plugs and wires
Cap and rotor.
Coil
Check primary wiring for damage, loose connections.
Really should do a compression test when plugs out.

Fuel and air filter.
Check status of tank internals visually.

If you're still running the original FI I'd also look closely at the wiring harness for it.
50 years is a long time. The plastic connectors get brittle with age and the terminals get tarnished.

You might try wiggling the FI wire harness while it's idling. Sometimes that's the only way to re-create the issue.

[worn]

Would it be correct to say that the motor runs smoothly when in neutral but cuts out when under load/ torque?

[PDXBob]

Would it be correct to say that the motor runs smoothly when in neutral but cuts out when under load/ torque?

Yes, idles pretty good when idling or even in neutral when raising RPMs to 2,00 or 3,000.

[PDXBob]

Thanks all. I’ll start working on various suggestions. Out of town for a while, but report back in a couple of weeks

[PDXBob]

When was the last time you overhauled your distributor?

I think I’ve overhauled everything on this car, EXCEPT the distributor. Can you tell me briefly what is involved, and I will also look for links on this overhaul. THANKS!

[iankarr]

Cutting out like that can be caused by obstructions in the gas tank (among the other things noted above). Do you notice the cutting out happening when going up hill? On during a turn? If so, it's possible you have some loose crud in the tank. Another thing to check is the fuel pump relay. gently pry the prongs apart a bit to ensure they seat properly in the socket.

[Fazasport]

I am going to speculate that you may have a problem with the circuit board in you Throttle Position Sensor. I had the same symptoms with my '76 914 and that was the issue.
You can pull the wiring harness plug off of the TPS and drive the car. If it does not miss or buck that is your problem. A replacement circuit board is available to replace the one in your TPS.

[PDXBob]

Cutting out like that can be caused by obstructions in the gas tank (among the other things noted above). Do you notice the cutting out happening when going up hill? On during a turn? If so, it's possible you have some loose crud in the tank. Another thing to check is the fuel pump relay. gently pry the prongs apart a bit to ensure they seat properly in the socket.

Thanks Ian. I’ll add your suggestions to my list. I’m starting with the easy (and cheap) stuff first. Huge fan of your videos, super helpful for us wannabe mechanics!
PDXBob

[PDXBob]

I am going to speculate that you may have a problem with the circuit board in you Throttle Position Sensor. I had the same symptoms with my '76 914 and that was the issue.
You can pull the wiring harness plug off of the TPS and drive the car. If it does not miss or buck that is your problem. A replacement circuit board is available to replace the one in your TPS.

Thanks Fazaspot. This is something I hadn’t thought of. Man, my list of stuff to check is long- but appreciate the support from 914Worlders! PDXBob

[emerygt350]

Not sure if the 1.8 has the same TPS as a 2.0... weren't all 76s 2.0s?

I was going to say TPS as well but my experience is from a d-jet

[Artfrombama]

My $.02
Engine missing under load. Classic symptoms of point gap too narrow.
Do the easy/inexpensive stuff first

[930cabman]

My $.02
Engine missing under load. Classic symptoms of point gap too narrow.
Do the easy/inexpensive stuff first

(IMG:style_emoticons/default/agree.gif)

Always go after the easy (cheap) items first. Could be as simple as a loose/frayed coil wire

[nivekdodge]

Like Olympic 914, I had a miss I was chasing and couldn't find or replicate. My freind Eric asked about plugs and i said they are new. But did you check them.....

Put the timing light on each one and sure enough....

New plugs and it was great

Kevin

[PDXBob]

I’m going through and checking stuff to try and get rid of my bucking issue. TPS works perfectly. On my 1975 L Jet it is 2 simple open/closed sets of “points”. One for idle and one for WOT. I also checked ground wires and they are good. Replaced spark plugs today.

On to the distributor!!! specifically the advance plates. A few questions: I want to see if advance plates move. How much should they move? How do I create suction into vacuum advance diaphragm? Could someone give a link to how to diagnose Distributor issues. I’ve used the googler, but I must not be putting in the correct terms.
Thx,
PDXBob

[nivekdodge]

I had a similar issue coming back from Okteenerfest.
It began during the drive while there,and continued during the drive home.
With 200+ miles to go and the missing getting worse, I started pulling plug wires and had a questionable spark on #3
Ultimately I found a Flaps and bought new spark plugs.
The ones I took out did not look THAT bad.
But have not had an issue since changing the plugs.

Might be worth a try.

Do the simple stuff first.

take the timing light to all the plugs, it will show the miss
Kevin

[ClayPerrine]

I am going to speculate that you may have a problem with the circuit board in you Throttle Position Sensor. I had the same symptoms with my '76 914 and that was the issue.
You can pull the wiring harness plug off of the TPS and drive the car. If it does not miss or buck that is your problem. A replacement circuit board is available to replace the one in your TPS.

This doesn't apply to a 1.8L. The 76 cars were all D-Jet. The 1.8L cars were L-Jet.


One thing to check would be the dropping resistors mounted on the battery tray support next to the double relay. They are notorious for breaking wires inside, and that will cause one, or all cylinders to cut out.

[brant]

Don’t forget to adjust the valves. Set fuel pressure along with all ignition and tune up steps including dwell points etc