engine stumbles/hesitates during onset of acceleration

MikeHynes

True Classic
10' BTDC also for carb-fitted engines you mean? I noticed that if I advance timing even a bit more the problem of the engine hesitating when accelerating gets better. It also idles a bit better when I put it more advanced, as if the engine likes it that way: Is there any risk of having ignition timing advanced beyond 10'BTDC? Thanks for your input Mike
I didn't take into account that this car has a Euro dist. I'm not sure how much total mechanical advance that particular dist has, but I'll assume it's pretty close to the amount the USA versions have?
In the end what's most important is the amount of advance at full advance. I know that's kinda hard to measure that without a dial back timing light though. I don't think you'll hurt the engine by setting the initial advance to 10' BTDC. You'll know that it's advanced too far if the engine starts to ping, or rattle - has pre-ignition. Some have assessed the SOHC combustion chamber as being pretty inefficient causing the burn to be slow. If that's the case more ignition advance is needed. I suppose a dyno can tell you how much advance is best, but a total of 36' BTDC is pretty conservative - IMHO. If that much advance worries you - use premium gas. Back it off if it detonates.

Bad news, I don't think that mildly retarded ignition timing is causing your stumble though.
 

kmead

Old enough to know better
I suspect much of your issue lies in the carb but as you have points, have you replaced your ignition condenser lately? A bad condenser creates all manner of driveability issues.
 
Before I had a dial back timing light, I counted camshaft teeth to measure advance. The is a little over 17 degrees of crankshaft rotation per camshaft tooth (tooth plus space) or about 8.5 degrees per half tooth (tooth or space). With a little interpolation, you can get close enough.

I did not realize this was a points distributor. That being the case, the dwell is important, as is the condenser as Karl mentioned. The condenser not only keeps the points from burning up, but along with the primary coil inductance, determines the waveform produced in the primary.
 

frank Jacobs

Daily Driver
Thanks everybody for your great help and advice. I will work through the suggestions you posted (double checking timing, checking accelerator pump, checking the inside of the distributor and will get back to you if I have an update.
 

frank Jacobs

Daily Driver
OK, time for an update about the engine hesitating issue (which is still not solved), and some potentially related issues that have started to appear in recent days...

Even though I am able to drive the car pretty well, the engine keeps hesitating/stumbling upon pressing the accelerator; It's really that single moment of acceleration, when I start pressing down the pedal that the engine hesitates and it gets slightly better with the engine at operating temperature. Beyond that, the car accelerates beautifully to at least 5000 rpm.

The ignition timing, accelerator pump and distributor were the suspected culprits: Here are some details on those:
- I double checked cam/crankshaft timing and they are correct. Ignition timing is set at 10 BTDC, because at 5 BTDC the problem is even worse.
- Accelerator pump seems to be working properly as I see a decent squirt of petrol when the lever is pressed.
- The car comes with what probably is the US-type distributor, with the vacuum unit attached and no condenser present

Then new issues are starting to emerge: Even though cold starts were fine about 2 weeks ago, right now the engine is more difficult to start, and runs on probably 3 cylinders for a while and it wont engage the 4th until I rev it for a little bit.

I am suspecting that the coil might be failing/underperforming and a weak spark may be the cause of my problems. It has clearly been in the car for a long time. The wires are new and everything is tightly connected. I hope to get your input on whether this makes sense, before I order a new coil. Can someone give me directions on how to test the coil?

Thanks!

Frank
 

Rupunzell

Bernice Loui
The ignition system is a Bosch EI unit?
If yes, check all connections, check the condenser for intermittent short.

More likely is the distributor cap and or rotor. If this exxe has a right angle distributor cap, it is possible the cap has an intermittent short causing mis-fire ignition. The other is the rotor, stock Bosch rotor has a resistor built into the rotor, if this resistor becomes intermittent, it will cause similar problems. Similar applies to a non-EI ignition system.

Not all distributor caps are created equal, the OEM Bosch units are mostly good. The aftermarket ones can be absolutely horrid to dead out of the box. The non-right angle cap from a VW, Porsche, Volvo and similar can be used if this exxe has the Bosch EI distributor and EI system.

Third would be a water flooded EI, water damaged EI unit which should be located on the RH hidden compartment above the power train compartment.


Bernice
 

Cratecruncher

True Classic
You can check the coil easily with an ohmeter. I just went through it on another car. Just look up the resistance specs using the part number on the internet. The primary coil is tested between "+" and "-" terminals. The secondary is tested between the "+" and center high tension lead to the distributor. Coils very seldom gradually fail but when they do it is usually due to heat causing a short in one or both windings reducing the total inductance (indicated by less resistance). Also check to see you have full battery voltage to "+" terminal with ignition switch in "run" position then turn it off before the coil overheats and shorts out, haha.
 

frank Jacobs

Daily Driver
The distributor on my X is a SE100EX type: Can anyone advice me on what components I could check to rule out (or blame) the ignition system? How can I check whether the vaccuum advance on the unit is working properly? Am I right that this type does not come with a condensator? Any other parts that could be checked for defects? Thanks a lot for your input!
 

Rupunzell

Bernice Loui
Pictures of the distributor-ignition system?
Pictures of the what the insides of the distributor cap and rotor?

Ignition wires/connectors can also be a factor, if they become intermittent or iffy, mis-fire of spark plugs is the common result.


Bernice
 
The distributor on my X is a SE100EX type: Can anyone advice me on what components I could check to rule out (or blame) the ignition system? How can I check whether the vaccuum advance on the unit is working properly? Am I right that this type does not come with a condensator? Any other parts that could be checked for defects? Thanks a lot for your input!
You can check the vacuum advance by applying a vacuum to the diaphragm while watching the engine timing with a timing light. The timing should advance when you apply the vacuum. Many modified engines do not bother using the vacuum advance at all. You might want to try timing the engine to 10 deg. BTDC with the diaphragm disconnected and see how it runs.

If it is a Kettering type of ignition (most are), it needs a condenser. However, it may be built in to the on board electronics.

Have you checked the total advance yet at speeds above idle (per the earlier suggestions)? Since that is not an original distributor, it might be a good idea to check it. It should top out around 30 degrees total advance somewhere in the 3,000 to 5,000 rpm range. The carbed cars had their stock distributors set for the higher end of that RPM range due to emission controls. The FI cars had full advance toward the lower end of that range which is what I would recommend if you are looking to optimize performance.

Most distributors have a centrifugal advance range of about 20 degrees. That plus 10 degrees static advance get you to around 30 degrees total. However, there are some distributors, including the ones on early X1/9s, that have about 30 degrees of centrifugal advance due to the emissions setup. That would lead to too much advance at high rpm. It would be good to check the advance across the rpm range instead of just at idle. Also, see if you can find the specs on that distributor.
 

Rupunzell

Bernice Loui
Ignition advance is important, but not that important. Keep in mind all available ignition advance should be in by 3,500_4,000 rpm. From then on, total advance should not be more than 32 degrees total.

"Vacuum" advance should be termed loaded ignition compensation as it bends the advance curve slightly with engine loading to aid in when the spark happens.

As noted before, driven street excess with a fixed advance distributor. Works ok with a performance modified engine and not allowing the engine to spend much running time below 3,500 rpm. Driving style dependent.


Bernice
 

fiatfactory

Steve Cecchele
The distributor on my X is a SE100EX type: Can anyone advice me on what components I could check to rule out (or blame) the ignition system? How can I check whether the vaccuum advance on the unit is working properly? Am I right that this type does not come with a condensator? Any other parts that could be checked for defects? Thanks a lot for your input!
thats an electronic ignition from a later model Fiat like an Uno etc.... I doubt that is your problem, look elsewhere.

SteveC
 

frank Jacobs

Daily Driver
Thanks all for your valuable input: I found out today that when I (accidently) drove the car with the vaccuum hose from the Vaccuum unit on the distributor unplugged, there is no clear difference in performance AND the hesitation problem.. It seems to me that this means I have a vaccuum leak somewhere right? I inspected the vaccuum lines and they seem to be without cracks, will give it a more thorough inspection later. Any suggestions are welcome.

By the way: Ignition timing is set to 10 BTDC.

Am I right in assuming that a vaccuum leak like this should give a noticeable effect in performance and could be the cause of the hesitation problem I keep having?
 

fiatfactory

Steve Cecchele
well your car was never fitted with a vacuum advance unit as standard, someone has replaced the distributor with another that has a vacuum avance unit, but we have absolutely no idea where that person has attached the vacuum hose to.... more than likely it's not hooked up properly, never was, and again I kinda doubt that's the problem...

SteveC
 

frank Jacobs

Daily Driver
You can check the vacuum advance by applying a vacuum to the diaphragm while watching the engine timing with a timing light. The timing should advance when you apply the vacuum. Many modified engines do not bother using the vacuum advance at all. You might want to try timing the engine to 10 deg. BTDC with the diaphragm disconnected and see how it runs.

If it is a Kettering type of ignition (most are), it needs a condenser. However, it may be built in to the on board electronics.

Have you checked the total advance yet at speeds above idle (per the earlier suggestions)? Since that is not an original distributor, it might be a good idea to check it. It should top out around 30 degrees total advance somewhere in the 3,000 to 5,000 rpm range. The carbed cars had their stock distributors set for the higher end of that RPM range due to emission controls. The FI cars had full advance toward the lower end of that range which is what I would recommend if you are looking to optimize performance.

Most distributors have a centrifugal advance range of about 20 degrees. That plus 10 degrees static advance get you to around 30 degrees total. However, there are some distributors, including the ones on early X1/9s, that have about 30 degrees of centrifugal advance due to the emissions setup. That would lead to too much advance at high rpm. It would be good to check the advance across the rpm range instead of just at idle. Also, see if you can find the specs on that distributor.
Thanks Don: to apply a vaccuum you mean just connecting a hose to the vaccuum unit and suck on it I guess?

I have not managed to check timing at speeds above idle yet, my timing light does not allow for that and I havent had the time to ask around. The engine has no trouble in the high end of RPMs, the hesitation is most pronounced at lower RPM, when speeding up after driving at a steady ~2500-2800 RPM; It will stumble for a bit and then pick up in RPMs. As long as I keep my RPMs above 3500 while shifting gears the car runs nice without hesitation or stumbling.
 

frank Jacobs

Daily Driver
well your car was never fitted with a vacuum advance unit as standard, someone has replaced the distributor with another that has a vacuum avance unit, but we have absolutely no idea where that person has attached the vacuum hose to.... more than likely it's not hooked up properly, never was, and again I kinda doubt that's the problem...

SteveC
Hi Steve, I am a bit confused, both workshop manuals I have show a vaccuum capsule attached to the side of the distributor, with lines coming out from the carb ?
 

fiatfactory

Steve Cecchele
Hi Steve, I am a bit confused, both workshop manuals I have show a vaccuum capsule attached to the side of the distributor, with lines coming out from the carb ?
that's simple, both workshop manuals are not for the model / market that your car was supplied for.

USA spec cars have vacuum advance modules ... European spec cars do not ... well X19's don't anyway. You have a distributor from an Uno /ritmo fitted, thats why you have a vacuum module on your distributor... but the car wasn't "born" with one.

You could check the function of the vacuum advance module. with the engine off, remove the distributor cap. By mouth, apply suction to the hose that runs to the vacuum module on the distributor, you should see the rotor move and then return when you cease suction... that will confirm the unit functions... if the unit is hooked up properly is another test... but as your carburettor did not come from the factory with the correctly positioned vacuum port, that's why I kinda doubt it's been hooked up correctly.


SteveC
 
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