[cal]

Hi has anyone encountered the problem below?

The car is perfect when cold but once it reaches operating temperature, the engine begines to hesitate or "jerk" when it reaches around 4000rpm.

My mecahnic has changed the throttle position potentiometer, the vacuum capsule below the air plenum, We have checked that the vacuum pressure is alright, we have swapped injectors with another car, swapped coils.

We originally thought that there was a problem with injectors that do not feed enough fuel to the cylinders and later we thought that the butterfly located inbetween the 2 air plenums was not opening enough but after the parts change the problem is still there.

As my car has a 2.5 motronic, there is no way to figure out the problem except through a trial and error process.

Can anyone advise what to do?


Regards,
Calvin Sim
Singapore

[Gcalo]

A few prime suspects:

a) air filters - check, clean or replace
b) fuel filter - can do strange things
c) lastly battery condition

A few good areas to check.

This does not preclude the possibility of a bad plug or coil assembly.

[io sono tifoso]

Originally Posted by Gcalo

A few prime suspects:

a) air filters - check, clean or replace
b) fuel filter - can do strange things
c) lastly battery condition

A few good areas to check.

This does not preclude the possibility of a bad plug or coil assembly.

Fuel filters can cause that, if they're clogged up they will let the right amount of fuel through until a certain speed, or RPM, which may b your problem.....

try to post on a forum like this one, or research the web before you throw parts at a car you can spend hundreds of dollars and not fix it or if it turns out to be the fuel filter it will be $30 or cheaper

also forgot, make sure you intake tubes or anything that provides air to the plenum is in the right place or not clogged may just be that its not getting enough air.

[Gcalo]

Fuel filters always cause probs at revs and so do bad electrical components.

I'd go the filter route first.

Great advice to search the site before spending.

[io sono tifoso]

Originally Posted by Gcalo

Fuel filters always cause probs at revs and so do bad electrical components.

I'd go the filter route first.

Great advice to search the site before spending.

yea i've thrown parts at cheap japanese cars, and i hated myself for it, but a Ferrari......man

[Boxer]

Could very well be a bad plug.

[Boxer]

Suggest you also PM Nightlife & P B-B. Both are 348 experts.

[Night Life]

Hmmm interesting I don't think it is a fuel filter from what you describe you have full power when cold only when engine warm you have this problem correct?
Also look for next time after engine warms up and problem arises open your gas cap and let me know if you hear air rushing in.

[Granucci]

Originally Posted by Night Life

Hmmm interesting I don't think it is a fuel filter from what you describe you have full power when cold only when engine warm you have this problem correct?
Also look for next time after engine warms up and problem arises open your gas cap and let me know if you hear air rushing in.

I agree and like this approach. There might be a clogged or [possibly] empty recirt canister and you don't want that. this car is about that age, and the canister is a PITA to get, but IF empty the bits get into the air intake valves and may cause some problems....doesn't sound like your problem but the whooshing sound on releasing the gas cap will be somewhat an idicator, as the canister solenoid might be toast and not allowing tank to get proper pressure. [I think I'm getting that correct?! ]

I am almost thinking that since at 4k rpm something else might be happening here. IT IS possible to upgrade IIRC--I've not need to do--to the next motronics.

PM also Dave Helms here and see what might pop up.

[Gcalo]

Ouch!

[Granucci]

Originally Posted by Gcalo

Ouch!

stub your toe? what?

[Gcalo]

I think Andrew may filter my comments!!

[Saint Bastage]

The rev limiter on the 348 is set for 7700 RPM (7850 on SS models). The issue your having sounds much more like ECU slow down limiters. I'd be making sure my Slow down light bulbs were operational then looking at, catalyzers, Cat ECU's, O2 sensors, cam position sensors and things like that. It really sounds more like an engine save system than anything else.

[cal]

Hi Guys, It great to hear all your advice, I will get the mechanic to do as suggested. Will keep everybody posted!

Regards,
Calvin Sim
Singapore