awilli6

Hey all,

89S4 with 160K on the clock was running fine with the exception of a shudder/studder at takeoff once it warmed up. Yesterday I unavoidably hit a pothole and the car immediately began running poorly (like it’s running on 4 cylinders). Transmission didn’t want to shift and when it did, it went into gear hard. I have it in the air and there are no leaks and the vacuum line to the tranny is in tact. Plugs and wires are fairly new. I changed the coils less than a year ago but with new/used ones from 928Intnl. Thanks for your assistance.

Ash

awilli6

I tried to upload a video of it running but it exceeds the 20 MB allowed.

Rembie01

You could upload a video to Youtube and post a link here.

I suppose it would have something to do with a part that could be damaged near the underside of the car. Thinking about parts on the underside, nothing really comes to mind. Do you remember which wheel(s) hit the pothole? It might give an indication to the possibly damaged parts.

As you said, it sounds like it's running on 4 cylinders so i'd suggest looking into the 4 necessities to make an engine run: air, fuel, spark and compression. Air could be a problem, MAF on ours was damaged. The thin wires might not have survived if they were already hanging on by a thread. Fuel seems unlikely. Spark should not be a problem, as you mentioned spark plugs are quite new as well as the coils. Compression also seems unlikely. But it does not hurt to check all.

Kind regards,
Rembert

awilli6

The rear passenger wheel hit.

Mrmerlin

Check the battery compartment see if the battery may have momentarily shorted out on the battery box ,
make sure you have a battery hold down installed.
Check the battery connections ,
then disconnect the ground strap for a minute and then reconnect it and start the engine

go to the computers in the CE panel foot well,
see if the IMR system has activated you will see a red or green LED in the relay,
this indicated a sensor has been triggered or bad temp sensor connection.put D100 on the sensor connectors.
keep an eye on your cats while trouble shooting ,
what you dont want is to see them glowing,
as this can cause a fire,
shut off the engine if this is happening.

do you have an IR gun?
if so start the car and check to see what exhausts are hotter than the others.
once this is done then swap the coil wires,
start the engine see if things change.

Next swap the connectors at the igniters on the front panel by the hood latch use the IR gun to see what exhaust ports are hotter,
this lets you test without exposing yourself to hi voltage by pulling plug wires off.

Also get a long screwdriver place it on each injector see what ones are/ are not firing/clicking

awilli6

Thanks for the list Mr. Merlin. I changed the IMR relay for a bypass a while ago. When you say exhaust ports, are you talking about the exhaust manifolds? Disconnect the ground strap. Are you talking about the negative battery cable or the engine ground strap under the car?

awilli6

All battery connections were tight. The temp on both sides are about the same but both seemed to reach 300 degrees pretty quickly. I changed both igniters when trying to track down the studder although they are not the same. Only one is a Bosh unit. Maybe I put the old one back on one side. I have changed the wires around once without a noticeable change in running. What should I look for when I change the wires?

I also disconnected and reconnected the battery. It’s running a little smoother but not totally smooth like before.

mj1pate

Very correct. A number of us have discovered that our cat matrixes are cracked/broken because of overheat during times that fuel is being dumped into non-firing cylinders, and completing combustion in the cats.

awilli6

Cats were removed and replaced with an X pipe

FredR

If you feel it is only running on 4 cylinders do some basic checks to find out whether it is the spark plugs that are not firing or the injectors that are not clicking.

awilli6

Thanks Fred. I’ll do more checks tomorrow.

Petza914

Open the battery compartment lid and post a pic of the underside of the lid and of the battery hold down.

mj1pate

+1
honestly, if something being jarred upset the engine operation, I would go over all of the accessible electrical ground connections and the electrical connections to “heavy” engine compartment components like the pair of coils. Make sure all those connections are sound, and not physically upset. Check electrical connections to the MAF and crank position sensor.
you may have to dig really deep for this, but I doubt it. Something has enough mass to shake itself free from a ground or electrical signal connection.

Mrmerlin

the exhaust ports are the 4 outlets on the side of each head ,
your IR gun can easily read each one and tell whats the hotter outlet about 1 minute after you start the engine.

still waiting on whats going on with the battery box inspection, and battery hold down plate.

awilli6