TomF

Just an update about my attempts to ascertain whether it is possible to change out an AOS in a Tip car without removing the engine. No one could tell me whether it was possible, so I took a deep breath and went for it. I can now say that it is possible, but appears to be a bit more difficult than a manual car. The issue is with the transmission itself and all the extras associated with it. I don't know whether my car being a C4 and a cab also complicated the DIY or not.

I used 450Knotoffice's excellent writeup as a guide and found everything to be pretty much the same, with the exception of the removal and replacement of the AOS itself. There is almost ZERO access and visibility to the AOS unit itself. I could see the bolts, but that was pretty much it. I had to remove and install the AOS unit itself completely by feel. Literally, I had to find the hole for the AOS to insert into by hand and the mounting of the unit probably took me 45 minutes, plus connecting the hoses.

All in all, it wasn't that bad, and I tried to keep the cursing to a minimum. My left arm looks like it got run through a food processor, but scars make the man!

One of the other issues I had was that clearly someone had blazed a trail before me and lots of hoses and wires were routed incorrectly and many of the clips broken. This made it very difficult to put everything back right.

A couple of suggestions- I would have a roll of vacuum line handy- those little buggers are incredibly brittle. I would also have a half dozen 3/8- 5/16 stainless conventional clamps handy as well. The old ones tend to break when removed.

I found that my AOS was leaking coolant from the top small fitting, and had been doing so for some time. The whole unit was brittle and crumbly around the smaller fitings. It was also leaking oil from around one of the seams in the body of the AOS.

It took me 6 hours to get the new AOS in and connected. It took me an additional 2 hours to reinstall the manifold, throttle body, etc... I could probably do it now in about 6 hours total.

Thanks to all that posted suggestions before and 450knotoffice for the DIY writeup!

dennis hiip

Good work. Thanks for sharing that. Although I wouldn't attempt this job, I now feel confident my mechanic buddy can do it if needed.

TomF

I forgot to add to the above that the plenums were a pain in the a$$ to get back in. The manifold went in fine, but the plenums were really tricky to get back in correctly and get the Vram solenoid in the right place. I think that next time, and hopefully there won't be a next time, I would mount the plenums loosely on the right manifold and attempt to get the left one back in under all the hoses... as 450knotoffice suggested, the ONLY way to get the front bolt in place on the manifold is to insert it before you put the manifold in. I only dropped the bolt once, and was able to retrieve it without too much trouble.

Here are some impressions after making sure everything was not leaking and in its proper place. The engine doesn't hunt for an idle speed on startup. It also idles nearly perfectly now as well. Additionally, and I am not surprised here, it runs quite a bit cooler than before with the temp hovering at the line at 180 rather than the "0" of 180 after a spririted drive.

I am going to have my local indy do a full coolant flush with the vacuum system as I have quite a bit of condensation-related gunk in the coolant. No oil, thankfully!

Given the condition of the AOS, it is clear that it is a wear item and should be replaced every 70-80K miles or so.

Next on the project list is plugs, coilpacks and plug tubes. Then on to CV joints and suspension... where does it end? LOL

jasper

I replaced my AOS while the transmission was out for a clutch replacement. The one that came out looked like new but for only $120 it was pretty much a no brainer, what with 75K miles on this reman engine.

Did you perchance cut the old unit open to see how it failed? I guess that would be a pretty messy exercise just to satisfy a but of curiosity.

Shark Attack

HA ha... I remember when I came here 2 year ago and told everyone I was doing my IMS myself, if we would have all been in a room all you would have heard was big gasps, whispers and pointing.

Good on ya! Whats the next DIY job?

TomF

Jasper, I haven't cut it open because it was clearly leaking coolant from the small hose nipple on the top. It also appeared to have spilt a seam where it was glued or fused together and was leaking copious amounts of oil from there.

Hey Kyle, I remember your great lead-in and writeup on the IMS. It was a great read to be able to follow your progress. Next is rear brakes (no brainer) and then on to CVs and changing out the tip transmission fluid as well as the front diff.

Gretch

Well you saved yourself at least $1,800 doing that job yourself. Conventional wisdom is on a tip, the motor has to come out to replace the AOS.

6 hours AFTER having done it once??????? I am all for dyi, but the fear of dropping a bolt in a place where I could not retrieve it........ sent me to the stealership.

TomF

Thanks for the comments. I should add that I have had 25 years of DIYs on 911s... I still count myself as a dedicated DIYer though, not an expert by any stretch of the imagination.

A total of 8 hours for this job isn't too bad. In the middle of the whole mess, I have to confess that I almost pulled the plug- my bruised arms coupled with everyone saying that it couldn't be done...well, I almost gave in.

It would be great if we could put together a DIY writeup on changing out the AOS on a a Tip cars. I love to prove people wrong! If there is someone local here in the Seattle area, I would lend a hand if someone else would take the pictures and do the writeup. Anyone interested?