355 Air Pump & Bypass Valve Questions

My mechanic diagnosed a bad air pump as the reason I'm not getting vacuum to open the exhaust bypass valve and the probable cause of rough idle and general power & driveability issues. On this advice, I purchased a replacement air pump and removed the 'bad' one last night. On a whim, I connected the old pump to a 12V supply and it works perfectly (of course AFTER I removed it....). Since my mechanic is on vacation this week and has been unreachable, any thoughts regarding what could be causing the vacuum failure to the bypass valve if the air pump is working fine? Unfortunately the idle and rough running issues persist but apparently the air pump is not the culprit.

 

Highly recommend that a compression test be performed for your rough idle issue. I'm not aware of any relation of the air pump and your vacuum problem.

 

Rough idle and bypass valve are not related. Find another mechanic.

 

Air pump is only for emissions, nothing to do with idling/drivablity. Maybe all you need is a change of spark plugs or check your fuel filter.

 

Check your fuse. I just saw mine was melted. If its to bad (melted box) I can tell you finding a replacement box is not easy as the 95 is not the same as the 96-99. I pulled my pump off and tested it and it only pulled 6-8 amps, so now I am going to replace the relay and keep an eye on it. While you are there check out your fan fuses to make sure that they are 30A and not 40A. If they are 40s then you also have a fan problem.

 

I can't speak to the air pump but the bypass valve and rough idle have nothing to do with each other. The bypass valve doesn't open until you're well up into the RPM range (depending on the load) so it being closed has nothing to do with idle. It sounds to me like you need to get a second opinion from a shop that is familiar with Ferrari's and has a SD2 to hook up to the car to start to properly diagnose the problem(s). Hopefully it's nothing major but those symptoms are too broad in scope to be able to really know what's the root cause without the proper equipment and, most importantly, experience.

 

your "mechanic" doesn't know what he's talking about.

The bypass valve on the 355 works on vacuum. There is a vacuum reservoir in the rear RH wheel house which is basically a sealed baked bean tin. It is made of top quality Italian steel and therefore corrodes and leaks. If this is leaking then not only is there no vacuum to pull open the bypass valve, but it'a also letting unmetered air into the intake system and contributing to the rough idle.

If the vac lines to the reservoir and valve are good & the reservoir not leaking then the other two elements in the system are the electric solenoid valve, also in the wheelhouse or the bypass valve itself. The bypass is easily tested with a vacuum hand pump. If you don't have one the other test is to disconnect the hose to the valve, lift the plunger manually, put your finger over the spigot and release the plunger. You should feel suction on your finger on the spigot.

The bypass system on the 355 is quite straightforward.

The secondary air pump has nothing whatsoever to do with it.

 

Thanks for the replies and for clearing up the mechanics of the vacuum/bypass valve system versus the air pump (bypass valve holds vacuum fine). Yes, I'm definitely concerned by the diagnosis, among other things, and waiting to discuss with my mechanic.

 

You're going back to the same guy after that diagnosis?

 

I would sure go back, to get a refund.

 

Breaking up is haaard to do.

 

Yes, I need to give him the opportunity to correct this. We've finally spoken and he's acknowledging the issues and assures me they will be corrected. I'll share the final vacuum resolution which seems to be the most difficult issue at hand.

 

Your air pump fuse is blown. It's common. Happened to me once. As for the other issues that I don't know.

 

Check the electrical connectors to the vacuum control solenoids and clean them. If the solenoid is not getting the electrical signal, it will not switch and allow the vacuum to open the bypass valve.
Also, I have heard that the MAF sensor readings can be impacted by vacuum leaks and you will get a P0102 code. Ask me how I know. Anyway, if a P0102 code shows up, the MAF information is ignored and the Motronic computer uses the TPS to approximate air flow. As a result, you get rough idle.

 

I am chasing a bypass issue similar to yours....my approach to repairs like this is system based. Understand the system, check each component and we should be good. Perhaps some of what I have done might help in understanding the system.

1. The air pump provides the vacuum to draw the bypass valve open.
2. The solenoid switch opens and closes at the direction of the Motronic unit
3. The valve itself is a simple unit that reacts to the vacuum provided by the pump and administered by the solenoid valve.

The fact that your pump spun on 12 volts on a bench does help...but really we need more data. Did you check the vacuum it was pulling? that would tell us that the pump has proper pressure....

Working from the pump to the valve. Splice in a "T" and attach a vacuum gauge to the vacuum side of the pump and start the car. Is the pump spinning now? If not, you have an electrical issue elsewhere because we know the pump does work....check connections & the fuse.

Do you have proper vacuum? 24 PSI if I recall....If so then we move down stream. If not...pump is bad even if it is spinning.

Next move the vacuum "T" to a point after the solenoid valve and before the bypass valve. This will sound crazy, but you need to pull a vacuum line into the car as we have to test the vacuum with the car moving. I forget the exact REVs but 4,000 in first gear sticks in my head. Anyway run the car in first past 4000 and look at the gauge. If you see proper vacuum, the solenoid valve is doing its job. No vacuum? the issue in the solenoid valve. Check connectors and/or cycle the solenoid with an external 12 volts and see if it is working.

Next test the valve. This is pretty easy. I used my air driven brake bleeder and set the air pressure to 24 PSI. Pull the line from the valve, attache the bleeder making sure it is tight to the valve inlet and pull the trigger. The valve should move to the open position. No movement? Bad valve. I shot a little video with my iPhone http://tessfamily.com/OIL/355ypassTest.MOV

Another less accurate way to test it is to pull the vacuum line, lift and hold the valve to the open position then put your finger over the vacuum inlet....let go of the valve. It should remain open...perhaps partially open as it needs constant vacuum for wide open. If it slams shut....well, bad valve.

If all of what we just did works, then the system should be mechanically functional as the only piece left is the thermocouple and ECU that feed the Motronic and if either of those are not correct you will get a check engine light and P1148 OBD code.

I am new to these cars so may have missed something....please feel free to correct me so we all have accurate data.

In playing with this 355 I bought, I have noticed a guy can get suckered into throwing parts at these things when they are not running right. Considering the cost that can get out of hand quickly.

Understanding the system, how it functions and how to check things helps diagnose the problem and not chase symptoms all over the place.

Best of luck.....

 

The car is back at the shop with the vacuum system being backtracked to identify the source of the problem. The emissions air pump is being addressed separately since it's not what's opening the bypass valve but does have a vacuum input. Not knowledgeable enough on the system to pass along more info now but will advise of the outcome.

 

The bypass system on the F355 is SIMPLER than any smog or vacuum system from any car from any country built from 1974 to 1991.

In other words, if the mechanic is guessing, he should not even be working at a gas station.

 

Good evening ladies and gentlemen,

after having quite some trouble with my new F355 on the vacuum system (burned fuse of air pump), I quickly want to give you my opinion on this topic/air pump issues.

Some of you have realized that the 328, 348, F360, F430 and F458 and many more do NOT have ITB's (individual throttle bodies), while the F355 has them. Their pro is a better throttle response, but the con is that such intakes are not suitable as vacuum sources (to keep the thread short, I do not explain here why). However, with the F355, Ferrari decided to still use it as a vacuum source.

This setup leads to an vacuum of appr. -0.2barg (-6 inHg) when engine is on idle and -0.5barg (-15 inHg) when revving the engine high and instantly closing the throttle).

On the F355, the "secondary air injection shut off valve" starts opening at around -0.3barg (-9 inHg) and is completely open with -0.4barg (-12 inHg). Pressure which the tank does not have during the first 2min of cold engine start, when the "secondary air injection system" is on and my engine is only idling to warm up the oil.

My conclusion: with the original setup, the "air pump" runs against a closed "shut off valve", with no air flow, heating itself up, and sooner or later welding its fan solid with the casing. Not to mention the (minor) negative consequences for the exhaust systems and environment when this system is not working.

My recommendation:
changing the spring of the "shut off valve" with a softer one. On my car, the valve now starts opening with -0.1barg (-3 inHg) and is fully open with -0.17barg (-5.5 inHg). Since I did this change, the air pump fuse stays happily in now for more than 7 months and 4000km. The softer spring and less closing force of the valve should not matter, since further downstream there are anyway check valves. By the way: the diaphragm type valve/actuator can easily be opened with almost no tools just by opening the snap fit.

Another conclusion: Ferrari did not care much about a proper vacuum system, since on the F355 it's not used for the power brakes as on most other cars of this era. Tuners that go from "Common throttle body" to ITB's usually install an extra air pump to overcome this problem.

Best regards from Switzerland

 

I am very impressed with this level of troubleshooting. It also explains why on 97 models, Ferrari introduced a cam shaft driven air pump.

 

well this thread offers some insight on similar issue my 1997 Berlinetta is having..but the OP never replied with an update since 2011.

long story short.. when I bought my car sept 2014.. I knew it had some issues to address.. brought it to my indie Ferrari mechanic..right away.

he got the SDL system corrected.. so that was good.

but my car had a rough idle.. at idle you can physically feel the car shake..
he cleaned tested all the injectors, all were good. plugs good.
compression test good.. all even 175 range..
opened the whole intake, cleaned all the injector ports etc..
put it all back together.

also my air injection pump was not working, fuse burnt.. cleaned it all up replaced fuse.. works perfect now.

bypass valve works.. but was not opening.. so for the moment he re-routed the vacumm hose so it stays open all the time..

no issues, no CEL lights etc..

he had the car for about 4 weeks in total, amongst other cars he was working on.

at this point it got to October.. so he suggested take the car, drive, and we'll tackle it in the spring..

I enjoyed the car very much for the last few weeks.. and then stored it.
car drove fine, nice power/response etc.. but that rough idle just drove me nuts.

one thing I noticed.. and why im thinking its in relation to this thread..
is on cold start up.. I hear the air pump whisle working perfect.. it operates for maybe 2minutes..

during those 2 mins when the air injection is on.. the idle is golden like a sewing machine.
then as soon as the air injection shuts down.. the rough idle sets in..

I read above, that there is that vacumm canister in the rear right corner.. and if its leaking, lets unmeasured air past the MAF.. which could cause the bad idle..?

this is what i observed up to now..

 

I have a couple bypass valves which I refurbished to better than factory specs, including stainless steel O-rings, if anyone is interested, shoot me a DM and I will discuss price.

 

Good afternoon,

the secondary air injection system has the task to inject fresh air into the exhaust to burn the surplus hydrocarbons that are there because the engine ECU lets the engine run "rich" during the 1st minutes of a cold-start because the cat converters and oxygen sensors are to cold to function yet. It seems your engine runs lean once this "enrichment" is finished and the secondary air injection system switched off and the lambda-control takes over. "Rich" engines typically run smoother than "lean" engines.

When troubleshooting anything with internal combustion engines, always keep the "combustion triangle" in mind: Oxygen (in our case part of the air), fuel and ignition source. In our case and because of the described symptoms, we better concentrate on the Oxygen-part.

On warm idle, the air flow is adjusted with the idler air regulator valve (throttle is fully closed) to adjust idle speed while fuel is controlled according the oxygen sensors in the exhaust.
Vacuum leak in the intake system can spoil all this control, depending how big it is. In your case its definitely a good idea to first check the vacuum system (on our cars easily accessible and the parts are super cheap) before changing any other expensive parts.

The quickest test (takes around 2min) you can do is following (pictures based on Bosch 5.2 engines which your 1997 for sure is):
- disable the vacuum system by turning both check-valves (part 20) on the vacuum source
Ferrari F355 M5.2 (1996+) Parts : Table 14 - THROTTLE HOLDERS AND CONTROLS
- disconnect the electrical plug of the air pump (part 40) to avoid damaging the pump because the shut off valve will not open anymore
Ferrari F355 M5.2 (1996+) Parts : Table 8 - AIR INJECTION DEVICE
- start the engine. When the warm-idle operation is smooth now, the leak lies somewhere in the vacuum system connected to these 2 check-valves (damaged hoses are "popular" on such old engine-out-maintenance cars, as well as rusted-trough vacuum tanks)
- don't forget to normalize all temporary modifications after testing

If this does not reveal anything new, check the integrity of following systems, which are also connected to the vacuum side of the throttle bodies
- hose to the fuel pressure regulator (part 9) and connecting hose between the throttle bodies (part 14) and check if pressure measuring connections are tight (part 44)
Ferrari F355 M5.2 (1996+) Parts : Table 14 - THROTTLE HOLDERS AND CONTROLS
- hoses of the idle air regulator valve (part 28) and anti evaporation piping (part 20)
Ferrari F355 M5.2 (1996+) Parts : Table 12 - AIR BOXES
- anti evaporation piping (part 2 and connected stuff)
Ferrari F355 M5.2 (1996+) Parts : Table 11 - ANTIEVAPORATION DEVICE
- hoses of the blow-by system
Ferrari F355 M5.2 (1996+) Parts : Table 12 - AIR BOXES

Since you cannot properly feel or hear vacuum leakages, a good way to detect vacuum leakages is putting smoke around the vacuum hoses and see if its sucked in somewhere. Another (non-EHS compliant) way is spraying engine start-aid spray onto the different vacuum systems, an accelerating engine would show you where vacuum system is leaking.

On my 1996 GTB 5.2 car which I bought one year ago, I had the vacuum hose of the fuel pressure regulator fallen off, a check-valve of the vacuum system damaged, a solenoid valve of the vacuum system broken and the plug of the TPS and knock-sensor swapped. Even the car was still running smooth, i had "CEL" lights popping up daily (after I realized that the seller removed the light bulp) and the car going to limp mode frequently (unfortunately not during the test drive nore PPI). After these items were fixed and (as previously mentioned) the air injection valve spring modified and the air pump fuse replaced, the car is running fine now and this already since 4'000km. However, also took me quite some days of my holidays to find out everything.....

Another good idea is to buy a OBD reader (cheapest are 20$, usable ones maybe 50...100$). Your 1997 US car is already equipped with an OBD2 plug. If you have an 97 Euro, most come with a 3 pin AWG connector for which you can buy/manufacture easily an adapter. With this OBD2, you cannot access all functions, but at least you'll be able to pull/delete the most important codes.

Best regards

 

thank you very much.. this is about the most detailed feedback on rough idle ive seen.. much appreciated.

as mentioned the car is stored now.. I look forward to investage/solve this in the spring when I get the car back to my shop.

having that nice smooth idle all the time, like on startup, will be that much more enjoyable..!

the repairs I mentioned above did help, and forgot to mention, a new set of ignition wires were also installed.

the end result was an improved idle from when I originally brought him the car.. but it wasnt still fully resolved..

since it was getting late in the season at this point, thats when he suggested to take the car, enjoy/drive these last few weeks.. he probably would have resolved it fully if I left him the car.. but I kinda wanted to take it too.. to drive abit..

I have confidence he will resolved it in spring when I bring car back..
since im not a mechanic, my inquiries here are to build knowledge for my owm understanding and in addition to better communicate/understand when im with him.

thanks again!

 

Terrific post and info Salbrech. Stay with us as many of us are in the dead of winter and the cars are hibernating but all the gremlins will come out of hiding as soon as the weather warms up.

I am very interested in your CEL issues. What codes were you getting? If you car isn't OBDII plug set up, how do you read your codes?

Do you think your SDL/limp mode issues were related to true hot cats as a result of your vacuum issues? The SDL system only measures CAT ECU output voltage , real or contrived due to issues with the measuring system. My point is, were you limp mode issues real as in true high temps or cat edu/TC/connection issues?

 

Good morning,
after I bought the car, I was getting the ODB codes "P0123 / TPS Circuit high" and "P0102 MAF low" (always happened after releasing the throttle with the engine running on ~3000rpm).

Unfortunately there were too many mistakes I fixed more or less at the same time without exzessive testing after each single modification.

So I cannot clearly tell you which modification cured what. I just now that is running fine now since a few thousand km.

Regarding the air injection, i am not sure what damage it might do during a cold-start without the "secondary air injection" working....


Regarding the OBD2: my car is a 96 EURO model with a 3 pin AWG connector. I manufactured a connector from AWG to OBD2. Of course the OBD2 reader for 60$ is always in the car.....