My 420 isn't feeling very well.
Can you help? Please!

Any owner having a problem with their Maserati can send me details and I will publish these, together with any subsequent advice I receive, on this page.

Just drop me a line at


Even if I don't succeed in helping you with your problems; and I do try, it would help other Maserati owners a great deal if you could let me know how you managed to solve your problems. THANK YOU!


Jens from Denmark writes:



Anyone know where to find a complete electrical diagram specifically for 420Si '87. Would like something with descriptions on symbols etc.

Thanks in advantage,



Jens from Greenland writes:



Regards to all fellow Maserati owners and what a great site this is!

I have 2 questions, that I hope some one are able to answer. Both directs to my 420 Si from '87 that I'm preparing for the summer:

1. I have on a German Biturbo website ( ) seen what they describe as a "time bomb". The German language is not my strongest side, but so far as I can understand it is a small internal oil filter in brass that will close by corrosion as time goes by and there by cause a terrible mess.

Any one familiar with this problem and able to describe it in detail in English and point out where this filter is to be found. Also how to eliminate the problem? Andy, I know about this one! I'm learning!

2. My power steering does not work correctly. Feels like steering wheel lost is grip around middle position and "floats" around. It was also fixed 10 years ago by my former workshop.

At that time I was informed that problem was caused by a white plastic piece inside power steering unit that had broken loose. For now I am not able to find a drawing showing those internal parts on power steerin unit. Any one knows what causing this problem and how to solve it?

Thanks in advantage,



Reply from Enrico and Andrea:-


Re: "Time bomb" and power steering.

"From the illustration below you can see the small brass filter. This can clog up over time, especially on a car that does not have its engine oil changed regularly. Once clogged up it will restrict or prevent the oil flow, and this can cause serious problems. The obvious cure is to remove this 'brass filter'.

While you are doing this, AND WITH THE CYLINDER HEAD REMOVED, you should enlarge the oil passageway of the brass restrictor within this oil gallery. This brass restrictor has a passageway with a diameter of 0.5mm. This should be drilled out to 0.8mm AND NO MORE!!! Make sure you then pass an air pressure hose through this oil gallery to clear out any metal shavings.

With regards the power steering, I don’t know what the white plastic bit is. The most likely cause of this is that the steering rack rubber mounts have deteriorated and you should replace these (very easy job) before you do anything else.


Csaba in Hungary writes:


"Hi Enrico,

I am writing you from Hungary. I have an `85 420, with a later injection engine. My problem is that in cold conditions if I start the engine the machine runs on idle for a while (for about a minute). Neither the electrician nor the previous owner knows why it happens.

Could you give me at least some clue where we can start? The electrician told me there is a part on the top of the engine (I think he was referring to the air temperature sensor), which he had never seen before; it was constantly working (also in case the car was not running). Could it be the problem?

Another question: is it normal in case of an injection engine that I have to push the gas in order to start the engine?

Many thanks for your help in advance,



Reply from Andrea:-


Re: 420 starting.

"Firstly, on an injection engine, you should not have to touch the throttle to start. If you are then this is the beginning of the problem. If you are saying that the engine will idle but not rev up for a minute then I don’t think this would be the air temp sensor, unless it is making the mixture so rich that it is flooding the engine with fuel. Have you tested the carbon monoxide level – should be 2.5%. If this is OK, I think the problem is more likely to be with the throttle potentiometer.



Matt in the UK writes:


"Hello Enrico,

I have a 1985 Biturbo 420 which is an import from Italy.

I am having trouble as the vehicle will not tick over on idle. First I thought it was running rich as the plugs and exhaust were sootted up but I put the car on a emissions machine and that said it was running weak.

I have altered the CO setting which has made no difference. Could you give me the CO setting with plenum chamber off and the location of the setting screw.

Also the ignition timing settings, also do you know of any other things that it could be.

Looking forward to your reply.

Thanks, Matt."


Tony in the UK writes:


"Hello Enrico,

I'm not sure where to start with this, but I'll try.

I have a 1987 Biturbo 420 Si imported from Italy. It has a 2.0-litre engine. I had a water pump failure and whilst removing the pump managed to tear the timing belt. This did not matter too much as I was to replace this anyway. However, the car has been standing for a while now and when I visited the car recently noticed that the cams had moved from their set positions.

The problems I have are:-

How do I remove the belt from the pulley on the crank? I have removed the 4/5 bolts on the outer edge of the pulley (inside) and can not get the pulley off. Does the whole of the pulley need to be removed? Or do I need to apply more pressure? I am mindfull of not wishing to rotate the crank incase any damage to the valves might be caused.

Secondly how do I set up the timing? Can I rotate the cams with out fear of piston meeting valves?!

Finally, is there a Maserati specialist or competant engineer etc on the South coast close to Southampton, Bournemouth or Portsmouth, who is not too expensive? This is in case I am unable to carry out the work myself.

Alot to ask I know, but if you can help, I would be grateful.




Reply from Enrico:-


Re: 420 Si timing.

"Hi Tony,

How do I remove the belt from the pulley on the crank? I have removed the 4/5 bolts on the outer edge of the pulley (inside) and cannot get the pulley off.

- So far, so good! But, have you also loosened the sensor capscrews and removed the sensor?

Does the whole of the pulley need to be removed?

- Yes.

Or do I need to apply more pressure? I am mindfull of not wishing to rotate the crank incase any damage to the valves might be caused.

- With the removal of the centre bolt and the four outer bolt you should be able to prise/lever off the pulley, using care and a little penetrating oil of course.

Secondly how do I set up the timing?

- I've posted the relevant pages from the Workshop Manual below .

Can I rotate the cams with out fear of piston meeting valves?!

- NO. It is not a safe engine.

Finally, is there a Maserati specialist or competant engineer etc on the South coast close to Southampton, Bournemouth or Portsmouth, who is not too expensive? This is in case I am unable to carry out the work myself.

Try Michael Jones (ex-Corley Motors - Maserati experts) on 01675 462860 (evenings only). He will come down for the day and work on the car for reasonable money plus travelling expenses.

Best regards,


Gijs from The Netherlands writes:


"Dear Enrico,

You must have heard this a thousand times by now, but once again: Congratulations on your website, it's a digital sanctuary for every Maserati enthousiast!

About a year an a half ago I purchased a Biturbo 420i of November 1986. It appeared to have some engine trouble, especially regarding cooling and oil fume ventilation. This resulted in a blown-up engine, about six months ago.

Fortunately, I was able to find a rusty Biturbo Si with a well running engine that could serve as a donor heart for my 420i. Since the Si has greater engine output, I wondered if it's strictly necassary to have the exhaust of my 420i replaced by a larger one.

The Si seems to have some more usable parts, such as suspension gear, which is slightly lower (and therefore nicer!) than the one on my 420i. I intend to have the suspension exchanged, but the 420i is the longer and a bit heavier car (plus 60 kg).

So my question is, does the suspension (or the car) need any adjustment to make it lower?

I look forward to hearing from you soon.

Kind regards,



Fernando from Portugal writes:


"Dear Henrico,

I have a starting problem for several years, unfortunately now it is getting worst. Sometimes when turning the key to start the engine, the starter motor turns, and so the engine but it doesn't fire up.

After trying lots of things, I discovered that taking the fuel pump and EAV relay, located in the engine bay, out and in, several times with the ignition on, then the engine starts immediately.

This was a nice solution, while it was efficient; in the moment, sometimes it only starts after lots and lots of tries. Examining the main components that are commanded by this relay I always get the air modulation electric valve (EAV), is it possible that this valve it is functioning erratically and some times work well and others no?

Before ordering a new valve I would like to know if you have any kind of experience with EAV valves or this kind of 'uncommon' failure in biturbos; I also find strange that the car, when starts well, it runs perfectly never showing any problem, until I stop and try to switch it on again...

Thanking in advance,



Reply from Rossano of Repartocorse:-


Re: 420 starting problems.

"I problema della valvola EAV potrebbe causare l'inconveniente, comunque questa la si può testare per verificarne il funzionamento, però consiglierei di controllare la pressione benzina ed il CO (analisi gas di scarico) in modo da escludere problemi di carburante e concentrarsi su problemi elettrici quali sensori e candele.


"A faulty EAV valve may be the root of the problem, this he should check to see if it's working properly. However, I would suggest checking the fuel pressure and CO emmissions (an analysis of the exhaust gases) to eliminate problems with the fuel mixture and concentrate on an electrical problem; the sensors and the spark plugs.



Djukic from Yugoslavia writes:


"Hi there!

My Maserati 420 Biturbo is carburettored.

Thanx , but where are going hoses from the carburettor, on what ??? and hoses of the turbo?

About the hoses I`m interested where are they going to (I now the begining of them), but don`t now where is end of every hose.

Best regards,


Reply from Enrico:-


Re: 420 hoses.

If you could send me more detailed photos showing which hoses need to be connected, I might be able to help you.

Meanwhile here are some pages from the Workshop Manual.



Francesco from Rome writes:


"Ciao Enrico,

1) Nel novembre 2001 ho acquistato una Maserati 420 Si 'Black'.

Dopo qualche tempo ho notato che il minimo si attestava sempre sui 3000g/m circa e l'auto non voleva sapere di ritornare al suo minimo prestabilito, questo succede ormai tutte le volte che la metto in moto, e l'auto praticamente e' inguidabile.

Secondo te e'un problema di elettronica? Tipo la centralina?

2) Esistono in commercio centraline per fare alzare la pressione del turbo?

Grazie. Un saluto da Francesco. Ciao."


"Hi Enrico,

1) In November 2001 I purchased a Maserati 420 Si 'Black'.

After some time I noticed that at idle, the revs would remain at (creep up to) around 3000 rpm and the car just didn't want to know about returning to its proper idle speed, now this happens every time I start the car making it virtually impossible to drive.

Do you think there is a problem with the electronics? The management system?

2) Are there any managent systems on the market that will increase the turbo boost?

Thank you. Greetings from Francesco. Bye!"


Reply from Andy:-


Re: 420 Si 'Black'.

"His problem sounds like either a dud idle control valve, a dud air temperature sensor or a bad body earth connection. If he wants to increase the boost then there are no management kits to my knowledge that are specifically available nowadays for that car but by removing the restrictor in the boost solenoid (the brown valve) he will get a significant increase in boost - careful though as protracted boosting into the red sector on the gauge will cause engine problems.




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