Can I use my spark plug connectors to check compression?
 

Hi, I have a second gen S4 a 1987 GXL to be exact and it has had a hot start issue for about 2 months. When I shut off the car and start it again (hot start) it cranks but doesn't start and then I would have to pull the EGI fuse, crank, then it would start up.

Now my car won't run, it starts up but the engine bogs alot when the tach gets below 1000 RPM and then it shuts off, I have to hold the throttle to keep it alive.

When I disconnect the T1 and L1 connectors the car still starts while T2 and L2 are connected. However if I do the reverse with T1 and L1 connected and L2 and T2 disconnected the engine won't start.

Does that mean my front rotor doesn't develop enough compression?


Thanks,

yes.

It does sound like low compression in rotor #1, but what you're describing also sounds like bad flooding symptoms. Putting the two issues together just makes the symptoms worse. Before writing the engine off as dead, do this to check for flooding next time:

1. Start engine & get it up to operating temps. Do whatever you need to do with the throttle to keep it running, then shut it down hot.

2. Wait about 5~10 minutes, then try starting it again. If it starts up and dies, let it be. If it actually starts & idles for you and wants to stay running, shut it down before it runs for more than five minutes.

3. Remove the leading plugs from both rotors, and describe what you see & smell - are either of them wet with fuel? If either of them are wet, it's flooding - probably due to leaky fuel injectors. Fix there is to remove the FI's and either replace them with new, or have them professionally serviced (i.e., cleaning & flow tested).

You still should get a compression test done, but if you find flooding as described, fix that first, and you might get more years out of the engine even with weak compression.

Its time to start with a rotary specific compression test. If the base engine you are working on has good compression then you can go forward with diagnosing fuel issues such as a sticky injector that may be loading up the combustion chamber. Typically poor hot starts are the sign of low compression however.