Engine has problem with #5 injector or coil.

[mattd1979]

I have a problem with cylinder #5 that surfaced shortly after replacing knock sensors and putting the top back on. The cylinder seems to run good when you first start the car but once your on the highway #5 cuts out and the car runs on 7 cylinders. When you come to a stop the car is loping. I'm not for sure if it is the injector or maybe the coil but the problem will come and go while on the highway. The car will be driving rough and then smooth out and gain power and then #5 will drop out again. My Mom is driving my car right now until I can get the fuel line replaced on her 1991 Q which will involve pulling her upper intake off also. What I need to know is weather or not this will damage the cylinder and piston due to not getting any fuel from the injector at times. I have been thinking that this lean condition may burn a hole in the piston. Please let me know if it is safe for her to drive my car like this until I can diagnose further as other then my car, she has no transportation until I get her fuel line replaced.ThanksMatt,Jacksonville, FL

P.S. does anybody know how I can check the coil to see if it is firing as the car is running and also check the injector the same way? Thanks again.

[3Q Jay]

yyou aren't worried that there is fuel, but no spark and washing the cylinder walls? Daedalus has a permanently low performing cylinder due to leaky injector. how do you know it's #5? do you have an IR thermogun? read the header pipe and compare to the others.

[Q45tech]

Check the harness connector for corrosion...........intermitent.

[mattd1979]

I believe that the harness may be the problem. When I had the intake off I was cleaning the connectors to the fuel injectors because they all had green fuzz on them like a penny if left in salt water and I may have bent the female connector prong to the point that it wouldn't make good contact once the connector was plugged back in. I noticed that it seemed to kick in when I botherd with the connector as it was running. The reason I know it is number 5 is becuase I did a balance test with the consult and all but number 5 was in between 110 and 120 rpm difference. #5 read at -10 rpm.

I am thinking about just getting a new harness for the injectors and replace the brittle one. I last heard on a post that was a couple of years old that the harness was $50 from Joe but I don't know what it is now. It may be the same as the cost of the knock sensor harness which was $75.

Speaking of knock sensors, after replacing the knock sensors I erased all trouble codes and after test driving the knock sensor codes never returned. The only problem now is that when I showered down on it, It began to knock and ping like bad gas but the knock sensors didn't seem to see it and try to retard the timing to avoid any damage. The only time that it would stop is when I'd let off the gas after flooring it. I use Amoco 93 premium and I had added a can of BG fuel injector cleaner just after this.

[maxnix]

The only problem now is that when I showered down on it,....

Could you explain what you mean by this please? Hopefully you don't mean you literally sprayed the top of the block!

[Q45tech]

WOT, getten on it = showered down.

The knock sensors can only do so much when even purported 93 octane [as sold ] doesn't meet oem specs.

These days impossible to trust pump stickers because the tests. are obsolete for modern engines.

With new KS an engine that knocks is being fed unsatisfactory fuel.

My Q knocked all Fall from Sept until Christmas.......then it totally went away when the fuel blends became normalized.

[maxnix]

WOT, getten on it = showered down.

Man, I am so not hip!

[mattd1979]

Q45tech,

Is there anyway that I can test the coil and injector while the engine is running to determine weather or not it is either an injector or coil? Please let me know if you can and thanks for all of the feedback.