athenian

I had my S4 Automatic on the lift last night trying to troubleshoot a hard shifting tranny problem....I was adding tranny fluid with the engine running for about 15-20 min...

My driver's side cat started to GLOW red and needless to say the underside of the car was very hot!! The left cat was also VERY hot but not glowing at that time....Shut the car off immediately and took off the exhaust (from the cats back). My first reaction was that the cats were plugged up since this S4 has NOT been driven on the open road for 2 years! It always starts up in storage and idles ok but the car has been sitting for a while....

Anyway, with the exhaust off and car running on the lift again after 20 min. the cats started glowing red (this time both of them but the driver's side more noticeably red hot than the pass. side)....I did a fuel rail pressure test and it's at 50 psi at idle...I pulled the spark plugs and I noticed that the front 4 plus were lean (very clean, whitish tip apperance) but the back 4 plugs were totally fouled (black tips)...Humm!!

I know that that 2 ignition control modules (top of the radiator housing) control different sparks and I thought maybe my module(s) are bad from sitting idle for this long...However, I checked my notes and I can recall that ignition circuit 1 (left driver's side) controls 1,7,6,4 plugs while ignition circuit 2 controls 5, 8, 3, 2 plugs...

Can someone verify that info on the control modules??

So basically, I have plugs 5, 6, 1, 2 (front 4 plugs) with a LEAN condition and plugs 7, 8, 3, 4 (back 4 plugs) with a RICH fuel condition!! Plus the engine is "missing" off idle and struggles to rev passed 4K RPM.

So I have my work cut out in diagnosing each and every problem....Suggestions are more than welcome at this point...Advice is also appreciated.

That's where I stopped my testing last night and hoping to continue troubleshooting tonight. Thanks for your time!

VK

'87 S4 Auto
'91 S4 Auto

RngTrtl

I have seen similar results in car that tend to idle alot and are driven rarely...A few cop cars, and several work trucks (both had occupants that like to sit and do nothing as the vehicle sat and idled for hours on end with the AC on). It is likely that the 2 problems are unrelated, engines are inherently bad polluters at idle and this can cause problems with the cats. I am not saying that this is what has happend to you, but it is likely. An Italian (or German in our case) tune up can help some if the problem is not too bad.

AO

BE VERY CAREFUL! SOME HAVE BURNED DOWN THEIR CARS BECASUE OF THIS!

This must be the 87, right? The thing about it being the back 4 is a bit confusing (to me).

I'm guessing either it's one of the final stages, a coil, a coil wire, or a plug wire is not functioning, but the engine is still pumping raw fuel in and it's getting burned up in the cat. Hopefully your cat has not melted. I wonder if this could also happen if you reversed some of the plug wires??

If this were your 91, the exhaust gas temperature relay would have kicked in and shut off the offending relays for that bank.

Needless to say, but I'll say it anyway, do not drive the car, and do not run it inside in case it should decide to go up in flames. A fire extinguisher would be good to have nearby.

dr bob

You will likely find that one ignition has failed. Possible causes are failed or disconnected coil wire, cap or rotor problem, possibly that ignition module. You can verify quickly by pulling one coil wire at the cap and grounding it. If the car runs the same (you'll know quickly), it's likely that you've found at least a solid symptom. If it doesn't start at all with one wire pulled, put that one back on and pull the other one at the cap and ground it. If it starts then, you have identified the issue for sure.

The problem with one ignition failing was serious enough that Porsche added a couple thermocouples and a smart relay starting in 1989 models, to shut down the fuel flow to cylinders that were too cold. It does this in banks with the ID's you list. For earlier S4's like yours, there are some horror stories about cat fires burning the cars completely. Your glowing cats description is a second sign of one failed ignition. First sign is soggy 4-cylinder performance, which you might not realize since you aren't driving. Third sign is your nerighbor or the fire department telling you to evacuate the house 'cuz your car is on fire. Glad you didn't make it past symptom two!

Gretch

Be VERY careful with yourself around the ignition system, especially the coils. Those are some bad boys and they can and will bite HARD if you do sketchy things with them. Grounding coil wires is an example of behavior that, done incorrectly, can knock you across the garage floor.

athenian

Okay folks, thanks for your suggestions so far...

I pulled each plug with the engine running and each coil is firing as it should and the plug wires appear to be fine. However, the engine was "missing" when revving off idle and the car was low on power when I took it for a short drive around the block this evening....It was "missing" quite a bit between 3K - 4K RPMs.

So there are multiple problems to diagnose here and my hard-shifting tranny is probably the least of my concerns right now...Tomorrow I will do a compression test to find out just how healthy this motor really is. It's definitely running sick now.

I swapped the 2 ignition modules from my '91 S4 to the '87 but it made no difference how the engine was running. So I concluded that my 2 ignition modules as working ok. I will also drop BOTH cats tomorrow just to be sure that those cats are not plugged (in the front) although there's quite a bit of back pressure exhaust coming out. However, I have no way of measuring that. There was no smoke of any kind from the exhaust and sure enough after 15 min. with the engine idling, both cats started to glow red again...I turned the engine off and called it an evening.

I will post any new findings soon....

VK

'87 S4 Auto
'91 S4 Auto

tommytomaso

if you keep getting them cats red your going to need new cats too...is it too much work to put some test pipes on till to fix this problem?

And is thier any sensors that the S4 crowed could use to warn them of burning cats......besides the burning cat smell..lol

athenian

That's what I'm going to attempt to do next....take the cats off and leave them off - besides I know these are original cats and most likely have passed their prime and are no good...I don't have any test pipes but I will fabricate something or just rip the guts out of the existing cats.

No, there are no sensors (like Ferrari 308/348/355 have) for the early S4 cars to warn of overheating cats....That's why some people have burned their 928s to a crisp while driving with overheating cats (someone above kindly shared that story). In my case, I'm not really driving the car....It's up on the lift running and I'm watching it spit out blue flames out the back! It's a cool (no pun intended) sight to see flames shoot out of a stock 928 exhaust!!

On a serious note, I'm not suggesting anyone should try this at home....Please use common sense. I do have my extinguisher close by and the car is up on a lift and I shut it down everytime the cats are starting to get too hot....I'm trying to diagnose my lean/rich fuel condition not to start a 3-alarm fire.

VK

tommytomaso

just cleaned out my cat, makes a nice sound now ........like two days ago..took me about an hr and half to remove and bash out it inards and re bolt.

WICruiser

Misfire as you decribe will result in raw fuel going into the cats as previously described. The fuel is burning in the cats, which is why they get so hot. Given the symptoms and your check of the ignitions I would guess spark plug wires are a good place to start. You also could have leaking fuel injectors that do not shut off and dripple fuel in all the time. Normally this would show up as a hot restart issue but it sounds like you may not have any experience with that situation given the limited operation.

If you are going to need cats at a later time for emissions I would replace them with a test pipe for now. They may be old but they still seem to work to some degree because if they were toast they would not get hot.

athenian

Thanks for the tip on the plug wires Roger....I have a really good set of wires on my '91 and I will test them on my '87 today along with swapping the coil packs as well. Just trying to eliminate possible causes at this point.

The engine starts and (appears) to idle well every time...no hot restarts even after coming back from driving the car around the block...Again it appears to be idling well within specs but the misfire and missing occurs off idle...I will gut the cats today as well and see what happens. I have an extra pair of used S4 cats sitting around for later use.

It pays to have more than one of these aging "mules" for testing ;-)

VK

Jim bailey - 928 International

It really sounds like it is running on 1/2 of the ignition system ....two cylinders on each bank. The none firing 4 cylinders (Two on each bank )are pumping fuel and air into the exhaust making the blowtorch/jet engine...If you have an inductive pickup timing light ...see if all eight plug wires make it flash. Gutted cats typically make a droning resonance at certain RPMs, like just about normal highway speeds And 928 cats those $2,800 units RARELY fail .

tommytomaso

Not that you'd like to sell me some cats...Jim..hehehe and cats go bad..sometimes for good reasons other times for bad...mine looked like it was from a hit....cats will mostlikly fail in the front part first...ie were all the heat is from and the front was not too good (oil or fuel most likly) but i had a busted section in the rear but the honey come was clean..
A good running engine should never burn out a cat but who knows what a PO did before.

PS. jim thanks for the parts i just got...cant wait till shes all back together. (Areo mirror kit, hood emblem, wheelspacers...whick realy make the car sit perfect! and a few other parts...thanks again)

athenian

Okay here is the latest update at the end of Thursday...

- Both cats are off the car (test pipes fabricated and installed)
- All plug wires and the 2 coils were replaced with good components from my '91 928 S4...All plugs are firing correctly and there's good spark on each plug...
- A compression test indicated between 145 - 160 psi on all cylinders.
- Pulled the front 4 spark plugs and they were bone dry! the back 4 plus were still fouled and wet (even after cleaning them).


So, it appears there's plenty on spark on ALL cylinders but fuel is getting only on the back 4 cylinders...Front cylinders (1, 2, 5, 6) are getting no fuel, but plenty of spark. The car still misses even at idle now and the missing gets worse off idle...No backfiring...The car is drivable but it's running like crap (low on power) ....To make matters worse, the Auto tranny is NOT shifting to higher gear when pressing on gas...If I let off gas, then it shifts to higher gear okay.

I thought maybe this problem was related to vacuum or modulator but a quick vacuum test indicated plenty of vacuum at the modulator...Visual inspection and the modulator looked fine. The tranny was just filled to MAX with Dextron III fluid and it's good to go.

Back to the engine problem, I'm suspecting bad injectors at this point but taking the fuel rails off to check for injector flow looks like a major pain in the butt...Any suggestion of how to get the fuel rails off (with the injectors still attached to them for testing) without having to take half the top engine apart??

The fuel pressure was measured at 50 psi at idle...There's old gas in the tank from the smell of it but almost empty.

It could also be that old gas gunned up some of the injectors so I've ordered some LUBRO MOLLY injector cleaner to add to my tank...It's good stuff and it works!

Tomorrow is another fun day!

VK

michaelathome

I haven't done it yet yet on the 928 but on a 944 you just gently pry each injector up after unscrewing the rail, it's the rings that keep them in snugged in place. I may have a complete set of injectors if you need them, they will need to be rebuilt but none the less for shipping I will send them your way. I have heard nothing but good things about http://www.witchhunter.com

Are you positive that your plug wires are on in the right order? Almost sounds like they aren't to me. From each coil you should have 2 wires running to each bank. I am not sure of the order ATM, would have to find the paperwork.

What is the pressure in your rails? Should be at 40+/- idle IIRC and higher under throttle.

Then again you are listening to someone that failed their VA inspection for a cracked steering bellow.

Michael