Some jerking when low revs, 87 Testarossa

Hi,
I just completed the first longer drive (300+ km) on my Testarossa. A wonderful day and drive. The car runs perfect now. Some minor issues still need to be fixed. But what I realised is some jerking at low revs (around 1500rpm up until just below 2000rpm).
It happens not really in first gear but in all others. When I am in 2nd gear and try to speed up slowly from 1500rpm the car might jerk heavily. However, when I full throttle it out of that rev range it is not really jerking.
When I am in 5th gear on the motorway in that rev range and I stay in it, it sometimes feels as if it is slightly misfiring - but only very minor.

Now here is some additional info:
- The plugs just got changed. It had it before and after the spark plug change. The spark plugs that came out of the car all looked fine (according to my mechanic).
- one of my cats is a little clogged up (already have a new one, will get changed with the next engine out service end of next year).
- the engine bay (maybe the exhaust) smells a little bit like gasoline sometimes. I couldn't pinpoint any specific location in the engine bay, so maybe it's the exhaust fumes.
- It just had a full service (oil change, new fuel filters, new spark plugs) but it had it before and after the service.
- Never had any fault lights in the dash come one.
- The car drives perfect otherwise and pulls nicely.
- It keeps temperature almost perfectly when driving on the motorway at 140kmh. Water stays just or well below 90. Oil barely comes up to 80 (with 80 being the dash between 60 and 100 degrees?).
- It starts right up when cold or warm. Just a beauty on warm start-up. One turn and she's there
- Idling is fine.

I read some threads on the forum that it might be:
- The clogged up cat plus maybe a clogged up pre-cat.
- Faulty metering heads.

Anybody has any ideas?
Best

 

typical sign of running lean. but I think this only happens when you accelerate slowly? when more than 3500 rpm all ok? if you can go so high in switzerland without risking going to jail and get the car confiscated
also it depends if you go up to the mountains. there the engine will run then also much more lean

can not remember now: you have cats? mine also is a 87 and never had cats.

 

Thank you. What might cause the car to run lean?
Yes, it only happens when I accelerate slowly.
Yes, when above 3500rpm all is OK. Already at 2000rpm, or at the latest 2200rpm everything is fine, no matter the gear.

All can be tested in Switzerland

Yes, I have cats. It is a Swiss version Testarossa. So, it seems to come with cats and pre-cats

 

try to disconnect the lambda sensors and measure the exhaust gases before the cat and adjust them to be equal

but you may also remove all that you can push down the plates from the fuel distributor and check if both plates move equal light

 

I had the jerking around 5k in high gear at full throttle and the issue was running rich.
Maybe the same happens in slow acceleration when it is running lean.
A tune should fix that.



Sent from my iPhone using FerrariChat

 

You sure it is not ignition?

 

What specifically about the ignition and how could it be checked?

 

My car did that until I fixed the cam timing with a degree wheel.

 

Plug misfire, Ign. wires etc.

 

So, the story continues and is not solved so far. Maybe someone knows what it might have to do with.
- The injectors were changed (new ones)
- The ground points were checked and are OK

However, it still shows the same jerking between 1000-2000 rpm, especially in 2nd or 3rd gear. And also some small stuttering when driving in 5th gear for example in that rev range, up to 2200rpm.
And also the idling is not perfect.

My shop did an exhaust check:
CO and HC are both high, CO2 low. They say it runs too rich (not lean).

Anybody has any ideas?
Best, alex

 

what you understand under high? numbers please

CO I would not care much, only HC

 

New spark plugs cured my problem.

 

If your shop has the ability to measure the exhaust gases, then they should be able to adjust the fuel mixture & air flow - I would assume?

 

Hello Alex_kay,
My 1989 non-catalyzed Testarossa is experiencing the same problem. A Ferrari mechanic pointed me towards an unintended air intake issue, and a Kjetronic mechanic suggested it might be due to low octane fuel. So far, I have not resolved the problem.

 

@turbo-joe I will find out for you. At the latest you will hear from me next Saturday

@ago car nut spark plugs were already changed and are brand new.

@carguy I am on it and I will report back once I know what exactly it is.

@TestaDDS I will report back once I have the solution. I hope to help out some people with documenting the solution

 

You have to adjust the idle according the manual. It’s kind of a pain to do it, but you must equal both sides of vacuum pressure at the correct rpm every time you mess with anything in the loop. Air, fuel, spark.

 

My mechanic solved the issue. Both oxygen sensors (lambda sensors) were broken. One was stuck at 0.81 and the other at 0.21. So one bank ran lean, the other fat.
Will change the oxygen sensors. At the moment I am driving with both oxygen sensor unplugged and the car runs perfect (compared to before). Probably with functioning oxygen sensors it will run even better

For the record: The original Ferrari parts number was 125881 which was replaced by 121515. And the Bosch number is 0258003009 (or 0 258 003 009).

Thanks for everyone helping.

Best, alex

 

I might add: It seems that Bosch is no longer manufacturing the 0258003009 (or 0 258 003 009).
They seem to have been replaced by 0 258 986 502 (or 0258986502) and 0 258 003 957 (or 0258003957).

Does anyone of you have any experiences with either?
https://www.boschaftermarket.com/de/de/ersatzteile/product-search.html?query=0258003009&prodKey=0258986502
https://www.boschaftermarket.com/de/de/ersatzteile/product-search.html?query=125881&prodKey=0258003957

 

two times the same bosch number?

 

Yes, I always try to include both numbers for the search function on the forum. When you for example search for "0 258 003 009" it will not show you the results for "0258003009" and vice versa.
Whenever I write parts numbers I try to make them as easily findable as possible for people having the same issue or looking for advice.

I did some further research and it seems the 0 258 003 957 (or 0258003957) is the replacement for the 0258003009 (or 0 258 003 009) and has the right plugs. I will try tomorrow when stores are open again, buy them and try them.
Best, alex

 

I never recognized a difference when searching if I use the x xxx xxx xxx system or if I use without spaces. I always look for bosch and then 10 numbers

 

Google recognizes that automatically and gives you the correct results. However, the search here on the forum does not. It gives you different results whether you use spaces or not in the parts number. And I try to make it as easy to find as possible for everyone hereonafter.
I quite often stumble across a forum post from years or more than a decade ago and I am so thankful for the person having solved that issue already

 

Alex, purchased two 0 258 003 957 for my 1986 Testarossa from RockAuto (on 1/1/2024 for $$35.79 each) and the plugs are identical to my originals. You may find a little more cable length on the 7-12 bank than you need though. EDoug

 

Oh boy, before I changed the oxygen sensors I did some digging while the old (supposedly dead) ones were still in the car.
I wanted to make sure the right oxygen sensor from the right exhaust was connected to the right ECU for the right cylinder bank.
What helped me was this great explanation https://www.ferrarichat.com/forum/posts/137085579/ from Steve Magnusson.
It is exactly as he mentioned in the thread. I only write this because the thread stops there quite suddenly.
"the single wire from the O2 sensor in the 7-12 bank exhaust stream should be connected to pin 8 of the forwardmost injection ECU

and, likewise

the single wire from the O2 sensor in the 1-6 bank exhaust stream should be connected to pin 8 of the rearward most injection ECU"

And it turns out: They had connected the wrong oxygen sensor. So, the oxygen sensor for cyl 7-12 was connected to the ECU for cyl 1-6 and vice versa.
They had even marked it wrong with a red pen.

Huge shoutout to turbo-joe who made me aware of that and asked me to check it before I put in the new oxygen sensors.
I will try to make it up to him when I meet him

Thank you all for helping me out in this. It is crazy that this can happen.
Best, alex

Edit 1:
This also explains why we measured 0.21v and 0.81v. If the oxygen sensors are connected to the wrong bank, the up or downregulate to the max and the other regulated in the opposite direction.
Example: sensor connected to bank 1 (but measures exhaust gases from bank 2) wants to fatten up mix. So bank 1 fattens up. Which in turn leads the sensor connected to bank 2 (measures exhaust gases from bank 1) to try to lean the mix. And on it goes until you land at the extremes of the voltage amplitudes (i.e. 0.21v and 0.81v; of course it could to 0.1 and 0.9 volts but they never work perfectly across the whole range)

 

good that you found the mistake. so no need for new sensors now?