Running bad ?

[98SF19]

Eric, you've probably read enough of thread to know that the OP and I are in the same boat. 2 questions:

- What indicators allow confidence that the injectors are the issue versus plugs and coils?
I'm currently having bad stumbling, mostly at low end, and getting no misfire codes, or any codes at all! When I had LIM out, I had disconnected fuel lines and left fuel rail on, thinking this would reduce the chance of needing injectors or seals from the trauma of popping rail off and back on. I noticed the injectors could spin between fuel rail and LIM but still felt tight. Upon reassembly, I put key to start a few times and let fuel pressure build. There were no leaks or hissing and I did a sniff test all over intake and fuel lines and didn't detect anything. These are original injectors. When I cleaned LIM I used a solvent that claimed to be safe for intakes and cats. Is there still a chance that I botched one or more of them?

- From your experience, can a gen 3 run with 3 misfiring cylinders?
Local dealer told me I had 3 missing - 6, 7, & 8, all on front bank. Whether this was a cop out or not I don't know since they refused to run full diag and therefore didn't access rear bank, but when connectors were removed from these 3 one at a time, I didn't really notice a difference in stumbling. Perhaps it would be hard to tell. I have 8 new coils on the way and will replace plugs as well. I guess if it's still stumbling bad after those, the injectors are most likely culprit(s)?

 

[E1]

A stuck fuel injector will often allow additional fuel into the combustion chamber than what it is supposed to.
Too much fuel and one gets incomplete combustion or an outright failure of combustion.
The coil fired, it just hit a wet plug and you got no 'bang'.
All that excess gas goes into the exhaust and the cats try to burn it off. A little bit of extra fuel = a little bit warmer cats.
A lot of extra fuel = glowing red, can't burn off all this gasoline cats.

The reason it would run better at higher rpms is that the fuel curves are higher and the amount of fuel allowed by the misbehaving fuel injector would be closer to the correct amount. Therefore the combustion chances are improved.

In my experiences, 96 and 97 SHO computers are dumb as a box of rocks when it comes to actually throwing a coil code.
A popular way to get the car to throw a code when it had an obvious bad coil but refused to throw a code was to unplug a front coil and see if the car ran worse and if the check engine light would finally come on.
If the car ran no worse, you probably unplugged the bad coil by chance.
If the CEL was set, pull the codes, NOW there should be 2 coil codes - one for the coil you unplugged and the other for the real culprit.

 

[GEN 3 SHO FAN]

I'm with Eric, starting with this idea, there is some possibilities (in probability order) :

1) not enought air is going to cylinders : check air filter or an obstructed intake, mass air flow contamination (metering incorrect air/fuel ratio, probable with a cone filter)
2) too much gas is going to cylinders : misfires causing gas going to cats (probable aging bad coils, bad plugs probable too, rear wiring harness is fryed on motor), spark plug on this motor don't have a gasket and if you bolt them too tight, they may break during the process (happened to me), ceramic part (white) broke causing misfires during month before the motor catch which one it was..., watch for oil into spark plug wells too (o-rings gaskets around all wells (8) must be changed like valve cover gaskets (5-8$ each)
3) (Eric correct me on that one) faulty timing : check/replace cam shaft position sensor and crankshaft position sensor (one bolt and 10$ each)
4) Faulty fuel pressure regulator (less probable, 1-2 case documented only) and check his little black hose meanwhile (According to the dates on faulty ones of TSB, 97 can have a faulty one. I have a 04/96 car and the date on my original FPR is around 94/09/14 then 97 car can have FPR of 95...)

(As you seem new here, I put some links here for you)
http://www.v8sho.com/SHO/fuelsysdesc.html
http://www.v8sho.com/SHO/CamCrankPositionSensorPhotos.htm
http://www.v8sho.com/SHO/HardStarting.htm
http://www.v8sho.com/SHO/MAFCleaning.htm
http://www.v8sho.com/SHO/SparkPlugChange.htm
http://www.v8sho.com/SHO/Blown Spark Plug.htm
http://www.v8sho.com/SHO/StartingGremlinsFixed.htm
http://www.v8sho.com/SHO/IntermittentNoStartProblemSolved.htm
http://www.v8sho.com/SHO/SHO97TRWireLoomFailure.htm
http://www.v8sho.com/SHO/RearMainWiringHarnessIssue.htm
http://www.v8sho.com/SHO/AllSHOandNoGo.htm (bad #8 coil causing interferences, start with that one. "The PCM was overfueling the engine based on an incorrect MAF reading. Yet, the analog input from the MAF sensor was good.")
http://www.v8sho.com/SHO/IntakeManifoldVacuumTest.htm (procedure to know if your exhaust is operating correctly, mufflers can be clogged too)
http://www.v8sho.com/SHO/RearCOPReplacementPhotosandHowTo.htm

Depending on your money and time, I will check these things before going with new mufflers.

Also you can ask you mechanic to clean your injectors with a product introced directly on the fuel rail. Worth the money (around 75$) for a car of this age. That will keep the motor nervous near as new (don't forget to put always high octane into it, this gas is cleaner and better for the valves at long term).

Good luck, hope it will help,