348 348 Odd throttle response issue - high revs - engine bogging etc

Recently replaced my throttle cable and broke a vacuum tube. Cut the tube, popped it back on the intake manifold and called it a day. I'm not sure if my issues have to do with a vacuum leak or not but here are my symptoms.

If I slowly ramp up my throttle in second gear I can get all the way to 7500 RPM without any issues. If I shift into third and floor it one of two things will happen, the engine will over-rev as if I missed a down shift or it will rev up past 5000, and then be stuck there for a while while sounding bogged down. I've heard that this 5000 or 5500 being a number for the camshaft sensors needing to be replaced. In general the engine seems like it's not getting enough of something once I floor it and I'm curious what it could be.

I also thought this could be my clutch slipping, but that doesn't make sense because we just replaced my slave cylinder a few months ago and the clutch was fine.

 

The fuel system is not keeping up with the injector demands.
That is:: it runs up to peak TQ and then falls flat as if it were not getting enough fuel.
Check fuel pressure and injector spray patterns.

 

This may make sense since the vacuum tube I broke went to one of the little fuel pressure vacuum cans. Maybe it has more damage than I thought. I'll check those vacuum hoses and if that doesn't work, i'll see about injector issues. If you have any helpful links, much appreciated.

The vacuum cans my tubes run to that I broke: https://www.ferrarichat.com/forum/threads/fuel-pressure.626088/

 

Sounds like the clutch is toast.

 

Could very well be. I have smelt an unknown burning smell recently in a couple drives. Maybe I'm at the bite point at stoplights far, far too long with the brake depressed. Curious to know if that's a sure fire way to toast the clutch. Need to hire a trainer or something to smack me upside the head for a day and teach me properly.

 

You do what?

put it in neutral, clutch out. Don't hold the clutch pedal down for an entire light!! That's not how any clutch works. Traffic can wait while you put it in gear and go.

sjd

 

I don't even hold it fully depressed at a stop light, I hold it at the bitepoint generally. Here to own up to my mistakes of being a bad stooge. Duly noted

At this point in the thread I'm sure I nuked the clutch then. I did this to prevent traffic from having to wait on me get it into gear and go. Saw a video prior to getting the car that holding the clutch at the bite point in traffic generally isn't a bad thing.

 

If your foot is floored (throttle) and the engine revs up but the car does not accelerate--it is the clutch

If your foot is floored (throttle) and the engine bogs down and does not accelerate or raise RPMs, it is the fuel or ignition.

The difference is whether the RPMs move with the speed of the car (clutch if fine) or not (clutch is not fine)

 

The exact sequence of events is once I let off the clutch, I floor it. The car revs up quickly to about 5,000 RPM and then sounds like it's bogging down around that area. Despite it bogging down, my speed is still increasing. If I hold The throttle long, It will begin to raise RPMs past 5000 and make the climb up the tachometer. It doesn't continually rev higher as if there's no clutch. I found a friend tonight about the clutch potential and after talking on the phone he said despite my methods at a stop light being wrong, since I haven't had the car along at all it probably isn't the clutch since the clutch was newly replaced a thousand miles ago. The clutch feels pretty grippy when in reverse or coming from a complete stop. My driveway is pretty intense and I haven't felt the car slip when going up or down it.

 

If it's something fuel related, then here's something that I found just a bit ago. If I put my head over this area here that circled in red, I smell fuel vapor. It's quite intense if I'm around 6 in away from this area.
Image Unavailable, Please Login

 

You're in a 30+ year old Ferrari, they can wait.

...and holding it at the bite point is a terrible thing. Whoever made that video you watched must think clutches are a maintenance item. Is this your first manual transmission car?

sjd
(I'm actually wondering if you're just messing with us...)

 

find where the fuel is leaking...quick.

sjd

 

I'm not messing with you unfortunately, but now I know and i'll kick it in to neutral when stopped at a light. I did learn in a miata many years ago from my dad, but I didn't drive it often enough to become excellent at it, rev match, and things like that. Some years later here we are with me owning the 348. So substituted with a lot of driving videos. I also did a 3 day racing course at skip barber to prepare for the driving portion, but the formula cars had an automatic clutch after first gear.

Looks like I'm going to try to find the leak. My car already drips oil like nobody's business despite every gasket on it being new within the last year. I think its just time for new hoses on a lot of this stuff though I believe the braided fuel line is new within the past year. I'll need to look at the previous owners receipts.

 

I think of it like this. The clutch pedal's natural position is with your foot off of it... how can I keep my foot off of it as much as possible.

 

Your clutch is shot if I interpret you comment. I.E. You let out the clutch and it revs to 5k while slowly accelerating (clutch is slipping). Then it seems to bog down (it has reached a speed where the load (torque) is lower and the clutch starts to grab. Then as the speed equalizes to around 5k RPM the clutch fully grabs and the engine RPM increase as it should with speed.

You can further test the clutch by trying to start from a dead stop in different gears and letting the clutch out completely. In 1st it may start pretty normally. In 2nd may slip a little. As you try higher gears it will slip more. If you try starting out in 5th and let the clutch out completely it should stall the engine of the car should buck.

 

If it stalls the engine in 5th, clutch is good?

 

If you put it in 5th and then try to move from a dead stop, just as you would if it was in 1st, it should either stall or bog the engine down if the clutch is good.

Another way to test is to start the car rolling in 1st, and reduce the gas to idle so you are moving very slowly. Then, without giving it gas, shift to 5th, let the clutch out fully. Once the clutch is out give it some gas, (not just a little). If the clutch is bad it should slip. If the car bucks a little and accelerates slowly without the engine RPM shooting up, the clutch should be ok.

 

I'll test this when I have time, I should probably figure out the source of my fuel leak (assuming there is one due to how potent the vapor is near the area I circled.)

Will look up how to figure out where a fuel leak is coming from etc.

 

BTW those injection check valves circled can melt if touching the engine and create an opening in them.

 

This sounds like the fuel pressure is a bit low--it is sufficient to fuel the car to peak TQ but not to peal HP.
This does not sound like ignition (ignition would be a staccato sound in the exhaust (and likely a CEL)

{{BTW I had this same problem in my F355 2 years ago--rubber surrounding the fuel pump in the tank had corroded into a "mess"}}

 

I've been leaving my gas cap really loose due to pressure build up. Could that cause it?

 

Yes, it could be the cause of fuel vapor smell. Pressure build up is normal. Put your cap on tight.

By the way, what gear are you in when what happens as described in your 1st post?

 

It can happen in any gear with engine bogging, but is most prominent in 3rd and after.

 

Double post, but doesn't something like a fuel pump help keep and make pressure or does the tank itself need to have the tight cap for said pressure to effectively build?

 

When you say it revs to 5k rpm, then bogs down, is the revving to 5k consistent with the speed (acceleration) or does the engine seem to rev higher than it should for the rate of acceleration, then bog down as the speed increases further?