Cylinder 7 not firing at all. - Forums at Modded Mustangs
 
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post #1 of 17 Old April 9th, 2014, 05:31 PM Thread Starter
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Cylinder 7 not firing at all.

My car has been misfiring and throws CEL 307 code. Also saw a 300 code once. Whichever cylinder it is, isn't firing at all. I changed the plug in cylinder 7, old one looked fine, new one looks like it has never been fired. Changed the COP for 7 and started the car... ran for about 30 seconds... it was still misfiring so I returned the COP and got my money back.

When the car sits overnight and I start it in the morning, it's rough and spits out some blue smoke and sputters for 15 seconds. Even after it's warmed-up, it idles lower than normal and will stall sometimes due to the low idle and misfire.

Only thing I can think to try is see if the fuel injector is leaky or clogged. Any suggestions?

---------- Post added at 03:31 PM ---------- Previous post was at 02:27 PM ----------

Also, there is a short hiss when I blip the throttle at idle, or rev matching, which I haven't really ever noticed before. I figured it is normal from the CAI, and I never notice because recently the weather has been nice enough to drive with the windows down... but just thought I would throw that out there. I don't know a whole lot about cars and I suppose it could be a vacuum leak for all I know.

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post #2 of 17 Old April 9th, 2014, 06:38 PM
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Have you pulled that plug to see if its wet after running? If its dry, you aren't getting fuel on that cylinder.
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post #3 of 17 Old April 9th, 2014, 09:12 PM Thread Starter
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good call man... I got home from work and pulled the plug in that cylinder and it was dry as a bone. I suppose the next step is to take out the fuel injector to inspect and clean it.... probably run some fuel injector cleaner for the other injectors too.... I run a 93 tune never any octane booster but never used injector cleaner either. What are the best brands? I have seen chevron techron thrown around.

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post #4 of 17 Old April 9th, 2014, 10:25 PM
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Most of those cleaners are BS. Try to find a set of take off injectors. They should be cheap. Stop running octane booster. Also, swap another injector to that cylinder to make sure it's the injector.
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post #5 of 17 Old April 9th, 2014, 10:35 PM
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Seafoam works really well. Agree with above post to move injector to determine if that's the problem.
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post #6 of 17 Old April 10th, 2014, 09:58 AM
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I have also heard good things about seafoam... never used it myself though.

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post #7 of 17 Old April 10th, 2014, 12:26 PM
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I would probably just buy a set of injectors or 1 injector. I'm sure you can find someone to let a set go for $20. Just easier than hoping a little bit of seafoam will make your injector work again. If I still had a set, I'd just send them to you.
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post #8 of 17 Old April 10th, 2014, 12:29 PM
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Quote:
Originally Posted by AnotherS197GT View Post
I would probably just buy a set of injectors or 1 injector. I'm sure you can find someone to let a set go for $20. Just easier than hoping a little bit of seafoam will make your injector work again. If I still had a set, I'd just send them to you.
This^

All those injector cleaners are BS. 100% agree.
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post #9 of 17 Old April 11th, 2014, 09:02 PM Thread Starter
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Thanks for the replies. I havent had time or money to do anything more and had to drive all work this week. Other cylinders are misfiring now, although no more engine codes yet. This weekend I am going to pull things apart and see what I can do. I am pretty confident it is getting spark because the brand new plug I put in 7 has clearly been fired. Someone at work suggested I check the fuel pressure to rule out the fuel pump and fuel filter. I am going to just change the fuel filter anyway, never been done since ive owned it.

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post #10 of 17 Old April 11th, 2014, 09:59 PM
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If you're saying the one cylinder was misfiring and the plug was dry because of no fuel, then other cylinders start misfiring, I'd say my next guess would be fuel filter.

Always check the cheap problem makers
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post #11 of 17 Old April 12th, 2014, 12:36 AM Thread Starter
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yea... I was just logging in because I was going to say, the more I think about it, the fuel filter would cause these exact symptoms. Car is pushing 80k miles and I assume the previous owner has never changed it. Going to do that on payday.

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post #12 of 17 Old April 12th, 2014, 04:09 PM Thread Starter
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I disconnected the ground wire from the battery for a good 20 minutes to reset the ecu, and sprayed down the MAF with electronics cleaner, neither helped. Took off the fuel filter and was easily able to blow through it; also the cover was missing a bolt and looked as if it had been removed and serviced before. I took it for a drive earlier and was smelling gas so I was already doubting the fuel filter was a problem. getting shitty gas mileage of course. I revved the engine and didnt see any smoke or spray on the ground behind the exhaust.

I plan to clean the throttle body and fuel injectors this weekend.

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post #13 of 17 Old April 12th, 2014, 07:12 PM
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Let's break down the things you need for good combustion.

Fuel- comes from the injector. Have you moved injectors around in the engine, to rule out the one in #7? It's not hard, as they are bolted down by the fuel rail and clipped into place. If your miss is still on 7, continue on. If not, replace all the injectors with some good take offs. They are cheap.

Spark- comes from the cop and delivered by the plug. You say you've changed both with no change, but I would double check by swapping cops like the injector with another cylinder.

Air- you've got that in spades. Otherwise it wouldn't run at all.

Compression- this comes from the base engine. Piston, valves, head, block and gaskets. You should have 150 psi compression on a good engine with your mileage. If it's lower, find the cause. Could be a lifter, roller follower, camshaft, valve. Even the piston rings can cause low compression. Pray it's not this.

Control- comes from the PCM and the wiring harness to the engine. The PCM supplies power and ground for the cops and injectors. So the wiring would need to be checked between the PCM and the cop and injector.



I hope this helps. Diagnosing a miss can be maddening. But it can be figured out.

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post #14 of 17 Old April 12th, 2014, 07:25 PM
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If it was a fuel pump of filter problem would not cause just 1 cylinder to miss fire.

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post #15 of 17 Old April 12th, 2014, 08:31 PM
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I wouldn't buy any parts yet, at this point you suspect the injector. It's not a big deal on the 3V motors to change injectors, simply swap #7 injector with #6 injector and when your engine light comes back on it should throw a P0306 if it is the injector. Try this and check back with us.

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post #16 of 17 Old April 13th, 2014, 08:08 PM Thread Starter
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I took the injectors out and cleaned them, looked at them... plugged them back up and left them out of the cylinders. Had my girlfriend bump the ignition key to On, and immediately the #7 injector started dripping fuel at a good pace. Maybe 1/3 the flow of an average public drinking fountain. Turned the key off and over the next 3 minutes the flow slowed down until it was a slow drip. I swapped the #7 and #8 injectors just for the hell of it, but I suppose I need to buy a new set, or at least 1. I just want to make sure it isn't likely something else like the computer being retarded telling #7 to stay open a hair... but sounds like as soon as the key turns on and the fuel pump pressurizes the rail, the #7 injector flood the head with gas.

---------- Post added at 06:08 PM ---------- Previous post was at 05:33 PM ----------

Where would be a good place to get injectors? Local auto parts stores want $60 a piece; American Muscle $210 for a set of eight; $180 from new takeoff.

Driver side; left is front of car. Bad injector is third one from the left. Cleaned them and the ports with some carb cleaner.


#7 injector

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Last edited by Nytrix; April 14th, 2014 at 03:21 AM.
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post #17 of 17 Old April 14th, 2014, 08:46 PM Thread Starter
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I bought an injector for 65 after tax. it helped but still misfiring in another cylinder. havent seen CEL in a few days. guess I need to return the one injector and just buy a set. still not 100% convinced replacing them all will fix the problem.

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