jeff spahn

I was reading through the multitude of threads on knock sensors and what have you and seem to have seen a thread though I can't find it now that said you can possibly take the water bridge out and get under the intake to change the knock sensors.

Anyone know if this is the case with my 90 S4? Sounds like it might not suck as bad as taking the whole intake off though a refesh might not hurt either.

I was looking under the hood and it seemed plausible but I just don't know.

AO

I don't think you can do it on the '90. On the 87 and the 88's you can (just did it this past weekend), but I believe the casting for the intake manifold is slightly different on the '90. The problem is the the rear bolt of the water bridge on the driver-side. We tried to do it on a '90 and couldn't get a bit on the bolt.

If you can loosen this bolt, then you can get at it. You'll need to remove the fuel line in the front of the engine and then pull the water bridge out. Then you remove the oil filler neck (good time to reseal it anyway). It will be blind, but you'll be able to access the front knock sensor after that.

jeff spahn

So then the rear you just get to from the rear then? I would guess my oil valleys in the casting by the water pump are filling up from the probable leak in the oil filler neck? Takes about 6-8 weeks to fill them.

BTW Andrew, I used your idea of the engine mount made of 4x4's to do the motor mount change. I varied it by making it of 2x4's but it worked well. Super cheap since I own a pallet and crating factory and I had everything in stock. Did have to buy the 1/2 x 10 bolt. Just wanted to say thanks for thinking out of the box.

If anyone wants to make one I'll post what I used and the dimensions needed. Specie of lumber is important. You CAN'T use 2x4 stud material, too weak. Need either Douglas Fir or Souther Yellow Pine.

SeanR

Why don't you just pull the intake and change the TPS, rubber hoses, fuel lines and get it all done at once?

AO

Well the rear knock sensor is a bit tougher to get at I think. If you're going that far, it really isn't much more work to pull the entire intake off. The real problem with the rear knock sensor is getting the rubber elbow off. You might get lucky and be able to access the clamp that holds it to the intake, but my guess is no. Even if you do manage to get it off, I'm not sure how much room you'll have to get at the knock sensor.

If both your fornt and rear knock sensors are toast, it's likely you have other things that need attention in the intake.

AO

As Sean points out, FUEL LINES are probably in need of replacement.

StratfordShark

That's very interesting Andrew. I was thinking of trying to remove water bridge without pulling intake (one of the coolant bridge bolts has snapped so may as well renew all the bolts and gaskets, and do the oil filler neck while it's off). People have done this on earlier S4s but looking at my 91 it does seem very hard to get an allen socket or bit on that particular bolt as it sits just under the intake.

I had the intake off on my previous S4, so will just repeat the job on this one and inspect everything once it's off to decide on what needs replacement.

Anyway yours is the first post where I've seen reference to a different casting so many thanks for solving puzzle.

davek9

It was a '91 that we were working on where the manifold had to be removed.

The rounded head Hex wrench will break off, they won't take the stress it takes to break loose those allens and you really need to get a straight shot down to seat the hex wrench.

https://rennlist.com/forums/928-foru...o-they-go.html

edit: here are some pic's from the weekend, I'm working my way down the front also if you take off the intake I would do all the parts that you can not get to (hoses, WOT, all 3 Knocks, etc.).

borland

S4/GT/GTS intake removal is easy.

Knock sensors should be replaced as part of the intake refresh, where faulty breather hoses are replaced. All fuel lines can be replaced without pulling the intake. Additional recommended replacements with refresh include flappy vacuum actuator and the idle control valve.

Another thing to consider with the refresh for automatics, is the GTS dynamic kickdown mod.

jeff spahn

I did the fuel lines already. Might as well do the whole intake refresh and get it done.
I'll search on GTS dynamic kickdown mod cause I don't know what that is.

Bertrand Daoust

If I were you I would definetly remove the intake and do an intake refresh at the same time.
Not a big job. It takes a bit of time but not a really hard job. It would be then very easy to change both knock sensors.

Mrmerlin

if your replacing the knock sensor then you will want to remove the intake as the V will be full of dirt and oil ,
you will want to clean out the mess and reseal the oil fill spout as well
i suggest to use Hondabond on the O ring for the oil fill spout.
and also consider adding the 928International oil fill block off plate to reduce oil spray, in the fill port

the flyin' scotsman

I made the mistake of not doing the water bridge when I did the intake r&r so last year when I did decided to do the water bridge/thermostat project I didn't want to touch the intake so 'squeezed' the water bridge out; just. In retrospect I should have just removed the intake.

I believe Dave C. also stated that newer MY cars cannot do the water bridge without removing the intake.

If you do decide to remove the intake I'd strongly suggest getting your hands on a diagnostic tool and check out the TPS, idle actuator, knock sensors and flappy BEFORE you take anything apart; you need a running engine. That way your not second guessing what parts to replace.

dimmer

Yup .. this is an all-in job. You'll be pulling the fuel injectors also. The clips can be a pain the first time. I made up my own tool by filing down a screwdriver (I'm sure there are better ways). You might consider getting the injectors serviced. I took mine to a performance shop in town that bench tested and cleaned them. They said that they really didn't need to be serviced .. tough to know that without having them serviced though. At the very least, I would replace the injector seals. After 20 years, most rubber or plastic parts near the engine have had it.

Tails

I have gained access to the knock sensors without taking off the inlet manifold.

The thermostat bridge allen headed set bolt at the rear of the RHS flange can be difficult to gain access, however, it depends on what collection of tools you have. I was able to get it out with out too much difficulty and when I replaced it I coated the threads with an anti-scuffing compound (anti-seizing compound) for ease of removal next time.

With the oil fill assembley removed I obtained sufficient access to get to the knock sensor for inspection, cleaning and some repairs, however I did not remove it, but I could have if needed be.

I was able to clean up the valley, removing the oil and debris and I renewed a crankcase vent hose as it had a large split/hole in it. I was also able to fit a split plastic covering over the electrical wiring after inspectiong the wire shroud and insulation.

I gained access to the rear knock sensor by removing the air filter housing, the MAF, however, to gain access to the jubilee clip on the inner side of the MAF took a little more effort, but I have a long small tang screw driver that passed through the inlet maifold inlet pipes. I used a small shrouded 12 volt globe assembly that I made to give me illumination inside the valley. This is the same light I made to check my flexplate migration via the hole in the bottom of the bell housing.

WIWIT I cleaned up the back end of the valley of oil and debris and by using my small articulated mirror on a extendable handle I was able to check my hose connections and hoses. I also ensured my vacuum connection from the inlet manifold to the 5 way rubber connector was secure and not leaking. I carried out my inspection of the aft knock sensor, checked the shielding wire etc, and install the split plactic piping to give more protection and extera shielding. I could have removed the aft knock sensor at that time.

When all was buttoned up, I had a diagnostic knock sensor check and all was well, and the knock sensors are still working satisfactory years later. I also have a vacuum gauge that I connect to the inlet manifold to check the vacuum at idle and at various RPM to keep a running check for leaks.

I do not do my repairs on my 928 by replacement, I check the function of an item, carry out cleaning, repairs and checks and if it functions OK great. I now have a osilliscope, so I can now check the wave forms from the sensors.

Tails 1990 928S4 Auto