Suddenly running rough
 

My car went from runnnig smooth to what feels like a dead miss only while driving. Idles smooth. Havent pulled plugs yet but have disconnected each fuel injector one at a time and found the same change for each one. Plugs, wires, cap, rotor, green wire, were all replaced around 6 or 8 months ago not exactly sure. The most recent change out was fuel filter and fuel pump. That was around a month or two ago. I dont hear any vacuum new vacuum leaks and everything appears connected. Anything sound familiar?

Replace your coil. Scrub your grounds, too.

Bad gas?

It could be lots of things, but is only revealed under load, which makes me think weak ground.

If you told us what car you have it would make it alot easier to help you. I'm assuming it's not a CIS car based upon your statement "disconnected each fuel injector one at a time "

Sorry, forgot to add that, 84 S US model. Speaking of coil, I got it from Auto Zone around the same time I did wires and plugs etc. Lifetime warranty on it and it was labeled Bosch on the part itself. As far as grounds, all have been cleaned that I know of. Question, can a coil just become weak rather than fail all together. Guess I could try replacing that for start. Its free.

Hot only Flat Spot
 

Good advice - verify the quality of your last tank of gas, the proper operation of the recently changed coil, check for faulty grounds and make sure that the rectangular electrical plug connector on the passenger inner fender well is not the issue. Next you might check that your fuel pressure is always consistent at the fuel rails. Then move on to whether your symptoms occur during a cold start and/or while running at operating temperature. One “Hot only Flat Spot“ that chased me around a bit came from an internal split within the brake booster. Later, the lady said that the brakes had progressively felt a little stiffer than normal but work fine. It was tough to keep a straight face after that comment. What initially snookered me was that when her engine water and air temp sensors enriched the mixture during the warm up cycle, the vacuum leak was sufficiently disguise to make it seem like a warm engine problem.

Good Luck - Michael :)

Check and recheck that your plug wires go to the correct cylinders. I seem to have a propensity to switch plug wires for cylinders 6 & 7. And I don't really know why, but when I have done work on mine and it's running with a miss, I check my plug wires and found more than once that i have switched the wires.

Well, according to the wsm, the coil is bad, probably internally shorted. New one is on order.

New coil changed nothing, but moving further into the flowchart in the wsm, the green wire resistance to pickup coil is 665k ohms which green wire itself is good and book says replace distributer. I was able to order a new pickup coil separatly. I will repost results when it is in.

Update, pulsed all injectors and found they all drop the same fuel pressure. Found cylinder number 2 plug wet, checked for spark and had spark. Would only make sense injector not spraying properly. Waiting for new injectors.

Sweet. Where'd you order from?

well, have to wait for payday, got a 98 bmw 328i for a daily driver since porsche seems to go down a lot. not sure whether i am going to send the injectors out for 38.00 each or buy them from auto zone for 37.00 each. They have gp sorenson which is probably a rebuilt bosch. cant wait to get this running smooth.

Wet spark plug could mean an injector is sticking open or not closing all the way. Maybe swap it with another injector and see if the problem follows it?

Cheap unknown replacement vs cleaning, I would go with cleaning.

Did you check resistance on all the plug wires?

Try pricing Witchhunter on clean/refurbish. Last time I sent some it was $17 ea.

Am thinking vac leak. I can rarely hear them.

looks like gp sorenson is a oem parts rebuilder. Also, i have tried running various injector cleaner with no results, cant see having a vacuum leak due to it being the second time i replaced the runner gaskets and boots as well as the injector seals. I also did a compression test on that cyl and it was 120. And i found some carbon buildup in the cyl using a tiny lighted camera. I am unsure how the injectors are attached to the rails yet. since the injectors look as if they are original, i think its time to replace them anyway.

well, off again, tried a used rail of injectors and cyl #2 still not firing. did the old school test of paper on the tailpipe, and the paper sucked into the pipe, guess its time for a valve job.

run a compression test first with the engine warmed up

cyl no 2 now firing, compression test was 120, intake runner bolt was bottomed out due to a previous broken bolt so runner had vacuum leak. added a washer to all the runners. Runs a little better but rich as hell. tried another jetronic, another air flow meter and another ignition module with no change. is there a cold mode for the jetronic that it could be stuck in?

check the timing marks at TDC,
Then while running the distributor timing

I think I found something
 

I removed the distributer to have a look since the way the car runs just feels so much like ignition. The pickup coil contacts are bent, dragging along on some of them. How could vacuum advance work when the pickup contacts are scraping and binding. I have a used distributer on the way to try. Hope I have something here so I can start posting about upgrades rather than repairs. Thanks everyone.

double check the fuel dampers for gas smell, if you smell gas in the vacuum line replace them all