Geo55

So since I have owned my 1987 S4 Automatic I have never taken the time to check its 0-60 MPH performance. So yesterday I thought that I would put a stopwatch to it. My times ranged from 8.1 to 8.2 seconds. When I did my upper end refresh TB and water pump I replaced the knock sensors also. Cam timing was done and rechecked with the Porken tool and was right on. I have also replaced the MAF with one from Roger. Only thing I can think of is the hall sensor. Is there a way to test the functionality of it?

FredR

If you disconnect the Hall sensor and there is no difference in performance chances are it is shot providing the knocks sensors are sound - a fault in just one of the knock sensors or the Hall sensor will knock 6 degrees of advance off the timing and that is significant.

I saw 5.7 seconds 0 to 60 in my late 90S4 - my expectation was 6 seconds so it was there or thereabouts and top end was where it was supposed to be so if you can only get 8 seconds that is a big difference. Same motor in my current 928 but no idea what the performance numbers are today- I have a feeling they are just the same or slightly better but...?

Geo55

Thank you Fred, that makes sense. But as you said, it could be a bad knock sensor too (that would cause the same problem?). Hopefully they are still good. I will try to get to it soon (within a week as I am a caregiver) and post my finding.

FredR

Knock sensors at that age are pretty reliable- thye tend to go south after about 15 years but there will always be exceptions not to mention after market knock offs. I rely on sharktuner to tell me that status of these items but without an analytic software capability one is left to deducing the problem.

Another point to consider however is that for reasons not clear to me the male connectors on both the knock sensors and the Hall sensor appear to fall apart when they get older- the body literally turns to dust, same with the CPS as I recently experienced. They can be rebuilt with a new connector - not such a big deal with the CPS and the Hall sensor but questionable value when one has to remove the inlet manifold to get at the knock sensors so not worth it with those items. I have just fitted a new CPS for that reason and temporarily connected each terminal on the Hall sensor separately as I had no spare- the repair worked as indicated by ST2 but how long it will last may be another matter.

Darklands

Is the Catalysator core collapsed?

FredR

I forgot to add that considering the above it is easier and less risky to disconnect a knock sensor to test for degraded performance

Zirconocene

@Geo55 : I am very interested to see what you find. My car is also slow right now (since I got it, really, but I didn't know that at the time). Right now I'm just throwing parts at what might be the problem, so long as they're in line with what I wanted to do anyway (SharkTuner chips, X Pipe/cat delete). If that doesn't make a huge change, my plan is to keep following the write up that RL has posted on the general troubleshooting area: vacuum leaks and issues with the fuel system (filter, dampers, regulator). Those are a little more involved so I'm taking the easy road right now.

ETA: Any chance you'll be at Camp 928 this year? I'd love to hear what you found, in person.

Good luck

Darklands

I think if you need 8,1 s 0-60 your car has 200 hp and something is seriously wrong. Running on 6 cyl. , wrong ignition wiring, MAF broken, clogged exhaust and so on...

Geo55

It has only been 3 yrs since I did my upper end refresh. That was when I replaced the knock sensors. However I did repair the connector on the hall sensor at that time. The MAF was replaced but a rebuilt at the end of last year. As far as the exhaust being plugged..not sure how to chweck that. I do not leak/ burn any oil to plug it. I will check the sensors by disconnecting them one at a time. But as I said, I do not have much time at this point in my life. But will get to it as soon as I can and report my findings Thank you all for your suggestions and positive comments.

FredR

The OP asked how to deduce if the Hall sensor is working [or not]. To understand the difference 6 degrees of retard makes is very easy to simulate.

If the OP is looking for suggestions as to the cause he is quite right to eliminate the retard scenario. As to potential causes for loss of power a commonly overlooked degradation is dirty injectors that can easily cost around 10% loss of power output across the board- Bosch injectors like our stock ones seem prone to this. Poor electrical components [distributor cover, rotor arms, HT leads] can add to the attrition as can blocked cats. Things like running with a cylinder down are easily detected - I once had an injector stick closed shortly after having had them cleaned and that stuck out like a sore thumb [to me at least]. The OP is savvy enough to not have a blocked air filter [or so I assume].

dr bob

Will you make it to Camp 928 this year? Even for a day? I'm sure someone can toss a diagnostic tool in their car and give you the definitive answer on what's working and what might not be.

Consider unplugging a knock sensor or the Hall sensor, then drive the car and see if there's any difference. You'd probably like to know some mixture numbers from the exhaust sensor. Grab your IR temp unit and read the exhaut pipe temps to see if there are partially-blocked injectors. Plugs tell you a lot. Lots of relatively easy things to look at even without a Hammer or other diagnostic tool.

Zirconocene

This is the article I was talking about: https://rennlist.com/how-tos/a/porsc...g-power-383830

There are some good tips in there for diagnostic work. Knock sensors, MAF, and other things are covered, including the exhaust and how to test for it.

Cheers

Bertrand Daoust

Also, make sure that it's well adjusted (bowden cable) and it shifts at the right RPM.
If it shifts to fast (early), you will lose some performance.

Geo55

I would love to go to camp 928 and see everyone, unfortunately I am tied up with taking car of an ill family member. Maybe next year. But for now I will follow the recommendations I have an IR gun and will check the pipe temperatures and unhook a knock sensor then hall sensor. Maybe pull and read some plugs. I also read the article on lost power and things to check. I will say that the injectors are just over a year old, but you never know right. I adjusted the bowden cable when did the tranny work, TT bearings and super clamp. Thank you all for your help and guidance. It is very much appreciated.

FredR

Although it is a somewhat obvious question and please pardon me for asking but did you get the injectors from a reliable source?

There is a lot of junk out there that on their own can account for a serious loss of power as some of our friends have found out the hard way..