: # 8 misfire



cj489
02-04-06, 11:09 AM
WE have an 02 DHS with a 4.6. We started getting service engine soon light. Caddy dealership says throttlebody and injectors needed to be cleaned. Also had two crank sensors which were bad. Thought I would change the sensors myself but did not have proper tools so took it to another dealership as the first one ripped us off before. So one thousand dollars later and the # 8 still misfires. New coil pack was installed on the rear but # 8 blew within minutes. Need help:want:

darcy
02-06-06, 08:24 AM
I just a problem with my 94 4.9 missfiring. the wires were only a little over a year old. i thought they were ok. found out that when you put in new wires and cap you have to put some dioelectric grease on or they will rot out. I found one of my plug wires did rot out. just something to look at.

JimD
02-06-06, 08:43 AM
WE have an 02 DHS with a 4.6. We started getting service engine soon light. Caddy dealership says throttlebody and injectors needed to be cleaned. Also had two crank sensors which were bad. Thought I would change the sensors myself but did not have proper tools so took it to another dealership as the first one ripped us off before. So one thousand dollars later and the # 8 still misfires. New coil pack was installed on the rear but # 8 blew within minutes. Need help:want:


Pull your trouble codes (DTCs) and list them for us to see. In particular, the "P" codes.

You have not explained why a coil was replaced on the 'rear'. Number 8 cylinder is in the 'front' bank.

cart69
02-06-06, 01:45 PM
number 8 is the front bank tranny side, or the farthest right plug on the front looking at the car.

my 94 had a similiar problem turned out to be wires. i replaced the plugs and it was fine for 40-50 miles then it started missing again

cj489
02-07-06, 06:12 PM
Changed out the spark plug boots but still have the misfire on # 8 which I found was in the front bank after reading the proper book. Replaced the coil pack and still had the misfire. Could the computer be sending the wrong message to the coil pack? Could the throttle bady sensor be bad but not throwing a bad code?

eldorado1
02-07-06, 06:18 PM
Have you tried just replacing that spark plug? If that doesn't do anything, you can depressurize the fuel rail, pull it off, and switch the #8 injector with the #6 injector, to see if the misfire code follows.

infin1ty
02-09-06, 09:32 PM
My '97 set a #8 misfire code. Had newer wires and plugs within 15k miles. Replaced #8 plug only - problem was solved.

cj489
02-10-06, 04:57 PM
I have replaced all the plugs, wires. When I replaced the coil in the front it ran fine without showing any codes then shot all misfire but only the # 8 was misfiring. I'm wondering now if there is a short or something not being grounded properly.

cj489
02-16-06, 05:52 PM
new problem: We drive the caddy to Tampa for the weekend and on the way home the misfire clears up, running like a top. Pull it into the garage shut it off, start it back up misfire has returned. Is there some typ of command in the computer gone array?

eldorado1
02-16-06, 07:03 PM
you can depressurize the fuel rail, pull it off, and switch the #8 injector with the #6 injector, to see if the misfire code follows.

^^^

Ranger
02-16-06, 10:25 PM
I just a problem with my 94 4.9 missfiring. the wires were only a little over a year old. i thought they were ok. found out that when you put in new wires and cap you have to put some dioelectric grease on or they will rot out. I found one of my plug wires did rot out. just something to look at.
It takes a lot longer than one year for rubber to rot. The purpose of dielectric grease is to prevent the boot from sticking to the plug. Not to prevent rot. If that were the case, then the entire wire should be coated, right? Infact new A/C Delco wires come with a message in the box that says not to use dielectric grease because the boots are coated with something at the factory. If your boots or wires were rotted in less than a year, there are other factors at play. I know that coolant (Dex-Cool anyway) does not play well with rubber (serp belts).

PAULSTSMAN1
02-18-06, 09:07 PM
With the 4.6 Northstar several things can cause a misfire. Some questions you might ask your are:

1. Are you losing Coolant? Could there be a HeadGasket issue?
2. Did you change the Fuel Filter? Dirty Fuel, or Pressure problem?
3. Did you see what the Spark plug you removed from Number #8 looked like.
4. Why did you change the Coil? Was it tested and found to be defective?

Recently I had a similar problem, my car has 109500 miles on it and I ran out of fuel, then the misfire malfunction started. I took my car to Tune Masters, paid for a diagnostic and found out #3, and 4 were the culprits. I was way over the 100K tune up recommended time, so I had all the plugs replaced, and the fuel filter. The plugs came out looking somewhat ashend, and old.

Bottom line, the car is now running like new! So much power, fuel economy up, and so Cadillac quiet.:)

Tune up and Speed shops that have OBII and III systems can figure out if your issues are electronical or fuel related. I find when I experience these problems private repair facilities can be much better than the Dealerships. Dealers techs often have a pull/replace mentality. You have already spent way too much money and time, not to have a decent diagnosis and resolution.

I hope this helps!

cj489
02-21-06, 05:52 PM
Whole new ballgame: Driving down the road 35 mph hear several pinging noises car dies we pull off to a side road and try to start the car but sounds like fuel pump problem. Tow driver arrives he tries to start it says sounds like a fuel pump. Towed to the mechanic and left for the weekend but we did return to gather things out of the vehicle. I thought one more time, vehicle starts but now is banging shut it off immediately. Mechanic looks at car on Tuesday says rods are knocking but it's full of oil and he has know idea. @001 4.6 had a ring problems being too soft, could this be the problem and one of them was broken or split. Please help.

eldorado1
02-21-06, 07:03 PM
Does the fuel pump prime for a couple seconds when you turn the key?

How severe is the knocking?

I know you said you replaced them, but it sounds suspiciously like an out of time/bad crank sensor. Run it out of time enough, and it will sound like your engine's rattling apart. Running it lean or out of time is obviously not good for it either, so get it looked into.

cj489
02-25-06, 09:25 AM
yes the fuel pump primes when you turn the car on, you can actually hear it. We are in touch with Cadillac and they claim we have to get the car to their shop in order for them to figure out what is wrong, duh. Thank you to everyone who has answered any of these posts. If I ever find out what has happened it will be on here.

cj489
03-12-06, 04:26 PM
Need an answer: Have the 02 deville in the shop. Mechanic says he took off the coil pack, took out the plug and the plug electrode was damaged as if something has struck it. The top of the piston has a hole through it. By the way this is the # 8 piston, which has all the misfire. What could have caused the hole?

eldorado1
03-12-06, 04:35 PM
Preignition, possibly detonation, running lean...

Got a pic of the spark plug? Is it just cracked with no signs of melting? That would be detonation. Could be caused by your bad crank sensors or bad gas off the top of my head.

Ranger
03-12-06, 04:44 PM
I would agree with eldorado1. The strange thing is that the Northstar has a spark knock detector that should prevent that from happening. That said, I can't imagine it could be anything mechanical unless the plug electrode somehow came off and got jammed between the piston and the head (if that is even possible) but I think that may be a stretch. How does he know there is a hole in the piston? Bore scope?