124 Spider (Classic) Engine shuts down at idle when warm

[MikeAyuso]

Ref: My 1984 Fiat 124 Spider manual 5 speed trans fuel injected 4 cylinder DOHC. 51K original miles.

Early morning start is perfect. Driving up the street engine runs perfect. Driving up the highway for a test drive, car runs very smoothly. Upon my return from a short trip of about 10 miles back and reach traffic in town, engine starts missing especially when idling or coming to a stop at the speed bumps. I would have to keep the pedal pressed at a higher RPM for it not to shut down.

However, my timing with my foot on the pedal in heavy traffic may cause the engine to shut down. Once it shuts down, it would not start. Engine would just crank and crank and turn but never starts. It would only start if I leave the engine off to cool off after about 15 minutes. It would start perfectly fine after that and the cycle starts over by driving good for a short while and starts with the same problem after the engine warms up in traffic.

I have done the following:
1. Cleaned the gas tank
2. Changed fuel pump using original BOSCH
3. Changed fuel filter
4. Changed vacuum advance by the distributor
5. Changed throttle positioning sensor using original BOSCH
6. Changed spark plugs

And still have the same problem.

Any ideas?

Regards,
Mike Ayuso

 

[eddiemc05]

Lovely car mike
Not sure of your history with it but as im a newbie here also looking help ive just seen ur post..

Prob cant help much as u seem to have done everything and very odd that its playing up only after a right bit of usage!
Would make you think of god forbid starting hgf or a crack somewhere ?
Have you done any compression testing?
Well i hope u get it sorted soon mike.
Atb

 

[MikeAyuso]

Hi Atb,

Thanks for your comments.

I took it to the mechanic yesterday to do a cocompression test and I got with the test results as follows:

Dry test:
cyl1 - 85
cyl2 - 85
cyl3 - 88
cyl4 - 95

wet test:
cyl1 - 120
cyl2 - 120
cyl3 - I didn't get a reading from the mechanic
cyl4 - I didn't get a reading from the mechanic

Honestly I am not sure how accurate it is. I say this because according the odometer it has 51K miles on it. I wouldn't know if that was tampered but I got the car at 50,700 miles on it and I have it only a few months and restoring it little by little.

One thing was mentioned is that the spark plugs were recently changed but seem very carbonized which might be caused by not having the proper air and fuel.

The mechanic did mention that the distributor needed servicing and will need ti reset the timing since he's take out the distributor for servicing.

I will wait and see what happens next.

Regards,
Mike

 

[eddiemc05]

Not sure on your engine but yeah its pos that old mechanical destributor could cause ur issues or similer if advancing mechenism was say sticking etc, is it points and plugs or electronic?

 

[MikeAyuso]

Not sure what your question is but it has a distributor with cables connected to each spark plug. Sorry I am not a mechanic.

 

[eddiemc05]

Ah no problem mike, im sure ur mechanic will have that area working its best before getting to the problem, hopefully a good clean up or even new cap and and leads might do no harm...
I hope its nothing serious at the end of it all...
Enjoy

 

[eddiemc05]

Btw theres a guy on here has an 82 spider, says temp sensor faulty, lennylin i think....
Good luck

 

[1997InA1976]

Step dad told me a faulty distributor will run funny as it warms up. His exact words were that my car will run better as the distributor warms up because mine won’t cold start anymore. But if an old distributor is temperature sensitive could be an idea.

 

[MikeAyuso]

Thanks guys. My distributor was tested fine. I was told by my mechanic that since the plugs are too carbinized after a short run even after changing the plugs is caused by bad timing.

Can anyone lead me to instructions on how to set the timing on my 84 124 spider?

 

[rallycinq]

Back to basics.

When the engine stops, what is missing?

Take a spare spark plug and check for a spark.

If there is a spark, pop a plug out, is it wet?

One or the other is missing, you need to find out which.

I am more used to the carburetor version of the twink, but I think you will have a crank sensor, these can fail with heat.

D

 

[MikeAyuso]

All 4 plugs have been tested for spark and all are good. One thing was noticed is that the plugs get really covered with carbon in just a short trip. None of the plugs are wet with oil, only the carbon build up. Also noticed the exhaust pipe is also filthy with carbon build up. Even running the engine at idle you can see the ground where the exhaust is blowing is also black.

Regards,
Mike

 

[rallycinq]

I've been doing a bit of studying, is your temperature sender working properly. You'll be looking for a gentle change in resistance as the engine heats.

If the temp sensor thinks the engine is still cold when in fact its hot, it will send too much fuel.

The other option is your cold start injector sticking open

D

 

[MikeAyuso]

I will have my mechanic check the temp sensor and injectors. One thing to mention is that the engine never over heats. The electric fan comes on and off automatically.

 

[MikeAyuso]

Okay I finally found the problem along with my mechanic. The Mass air flow sensor switch was causing the problem. There was some slight adjustment made to it. It has part of the surface worn out where the copper needle passes over at the bottom end where pointed in the attached picture. In the interim, the needle was adjusted a bit for it not to reach all the way down. Since then the engine runs a lot smoother, and when it's hot it does not shut down. It still misses a bit when hot but does not shut down. I will need to get this replaced.

Regards,
Mike

See attachment.
https://www.dropbox.com/s/ukc10nmh7reqtpy/84_Fiat_spider_Mass_Air_Flow.png?dl=0