jlegault

I have a 928S 1983 4speed Automatic that I baught from a guy in california with a deffective transmission. I changed the tranny with a used one and now I am facing an engine issue: the engine won't rev easily. It idle smooth and rund smooth even when I try to rev it. On the road, it's like if the throttle sets the rev: the more open is the throttle, the more rev I get. If go on full open throttle, it can do the 0-60 in ~7 seconds, which I think is the spec.

Here is what I have done so far:

- Checked and replaced all the 'rubbers' in and around the intake.
- played with the timing (I dont' have a timing lamp yet but played wit the timing a little bit at the time)
- Checked the cam timing
- disconnected the O2 sensor and forced the full throttle switch to ON
- Pushed on the AFM plate to simulate more air flow (and hopefully enrich the mixture).
- Opened a vacuum hose to let un-metered air in the intake (to lean the mixture)
- Changed the sparkplugs (that was last year, when the idle wasn't really smooth)
- Verified the resistance of the AFM and temperature sensors. The AFM resistances are within the values of the later AFM as per the workshop manual (i.e. twice the values of the previous generation of AFM). but the Temperature sensor on the AFM has a resistance value that corresponds to the previous generation according to the workshop manual... Can the workshop manual be wrong for that one?

Because I can have 0-60 in ~ 7 seconds, I don't think it can be fuel pressure or friction in the tranny.

The next things I will do will be to take the tranny down once more ($#%#@) and try the engine with no tranny (I have to change the torque converter seal anyway @#*&^@$#)

I will defenitely check the timing when I get a timing lamp in a couple of weeks.

I definitely need some help on where to look . Is there a way to check if the air-fuel mixiture is good by using the O2 sensor? What kind of test can I do on the ECU?

Thank you in advance for your help.

Jeff

Randy V

Hmmm, not really sure what type of problem you are describing.

Have you checked that the catalytic converters aren't plugged?

ErnestSw

You're saying that you need to press down on the accelerator to open the throttle to make the car rev higher and you can do zero to sixty in 7 seconds. What am I missing here? Oh please, kind sir, help me understand what your problem is.

G Man

I'm confused.

heinrich

Jeff, to fix your problem, you need to use the gear shifter. Set it to "2" and "3" and see how you like it.

jlegault

The problem is that the engine is not nervous. It is my first 928 so I can't compare with another 928, but I feel it is not normal that I need to depress the accelerator to 50% to rev the engine up to 3,000 RPM. On all the other cars I've had (includeing a 924S), I just slightly press the accelerator and the engine nervously rev up to 3,000 RPM; another slight push and it goes to 5,000 RPM. So the problem feels like if I had a bad timing or a the belt has just skipped a tooth. Because the engine doesn't rev easily it makes the automatic transmission shifting a bit erratic. I played with the timing with no success. I checke the cam marks at TDC and they are aligned with the marks on the cam case.

Is it possible that the cams are shifted by few degrees even if the marks are OK?

Can someone with a 4.7L engine and AFM tell me how much does the accelerator need to be depressed to reach 3,000 RPM or 4,000 RPM on neutral (e.g. 1/2" at the top of the accelerator).

Is there an easy way to check the air/fuel mixture? With the O2 sensor?

Any ideas?

Thanks

Jeff
928S 1983 4speed Automatic

AO

Jeff-
What you are describing sounds normal to me. It is a very linear relationship. If throttle response is slow I would suggest removing the cats, and maybe check ignition timing. Cams should be lined up, but it's possible one cam jumped a tooth, but pretty rare. Unfortunately, there no easy way to set cam timing on the 16v engines.

Remember this car has a V8 and gobs of torque. It was designed to be a GT, not a go-cart, so it will feel very different from a 924.

BTW, welcome to Rennlist.

WallyP

My first suggestion is to find another 928 owner nearby so that you can drive each other's cars. This will quickly tell you if your car has a problem.

Best way to start is to give your location...

jlegault

I still think that it doesn't rev as it should. I understand that this is a big V8 engine and will not be as nervous as my 4cyl. on my 924S, but it doesn't rev enough to match the shift points of the automatic transmission. Is there a table that shows the RMP vs. Throttle position?

Thanks for your help.

By the way, my wife starts to tell me that I shouldn't have baught this car (@#$@*&#) because I have been working on it for almost 2 years now (the transmission took most of my time), but I just love these 928s and would like to enjoy driving mine soon.

Jeff

jlegault

I am in Fort Wayne, Indiana. I am willing to do a little drive during this Thanskgiving weekend if someone within ~100 miles has a 928 that I can compare with.

Thanks

Jeff

AO

Jeff as Wally (serious 928 Guru BTW, ) suggested, it would be good for you to compare your 928 to someone elses. Where are you located?

But from your last post, it sounds like your issue is not with how the engine revs on its own, but how it revs while driving (under load). Is this correct? Throttle position should have nothing to do with it as this is an arbitrary measure. I've not driven a 924, so I don't know what the gas pedal feels like in that car.

Does your car feel like it's shifting early? Maybe not revving to redline? If so, it could be a couple of things, but most likely the addition of a kickdown override switch will help liven up the performance. I've only had manuals, but I think it's just a matter of putting an inline switch connected to the leads on the kickdown switch under the gas pedal. 5-minute install - if that. Give it a tray and see if that improves things.

jlegault

The tranmission doesn't up-shift unless I release the accelerator. There are 3 things that influence the shifting points: accelerator position, oil pressure (proportional to RPM) and speed. So when I accelerate, I have to presse on the accelerator a lot to get a decent acceleration; the engine doesn't reach the RPM it is supposed to for the accelerator position so oil pressure is too low for the transmission to shift up.

This is all from my understanding of this automatic transmission... And I agree that it will be very instructive if I could check with another 928.

Jeff

heinrich

Have you left the car in Drive or have you been shifting manually?

heinrich

If you can get to 7sec 0-60 on that car your engine is fine.

SharkSkin

Double-check check the bowden cable adjustment vs. spec, make sure the vac line is hooked up properly. Not sure if you have a kickdown switch, but if you do, check that too.