Random Misfire Please Help!

Tiny
KIRTIS9957
  • MEMBER
  • 2003 CADILLAC DEVILLE
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 120,000 MILES
Misfire 03 deville. P0208 p0300, started off with p0308 as well then went to random changes plugs coil packs fuel injector #8 map, maf sensors. Checked volts to injector and for Shorts from pcm to injector. Haven't checked compression because after I've took to different mechanics it runs perfectly fine. And they claim they done nothi g but look and reset with there computer. About 3 days of running smooth SLOWLY misfire comes back. First only when I start the car then will go away to having to drive about a mile to finally heavy nonstop misfire. Pcm?
Monday, December 28th, 2015 AT 5:07 PM

16 Replies

Tiny
KIRTIS9957
  • MEMBER
  • 10 POSTS
Plus car smells heavy like gas, I mean heavy. Haven't used noid lights but volts with key on is good. Wire from pcm to number 8 has no short. Don't mean emphasizes but I'm desperate!
Was this
answer
helpful?
Yes
No
Monday, December 28th, 2015 AT 5:15 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check fuel pressure then if it comes back have a mechanic run freeze frame on it see what if any sensor is screwed up. Also check for a vacuum leak. Fp should be 41-47 psi key on only
Was this
answer
helpful?
Yes
No
Tuesday, December 29th, 2015 AT 9:40 AM
Tiny
KIRTIS9957
  • MEMBER
  • 10 POSTS
I haven't checked fuel pressure but multiple mechanics have looked at freeze frame and came up with map sensor and o2 sensor. They've also told me that no vacuum leak could cause a misfire so bad. But visually have checked and looked good. I'm a pretty fast learner if you can explain what I'm looking for on freeze data. I just really think its pcm or sensor slowly dying because. After mechanics clear codes car runs fine and slowly diminishes. What's the difference between me clearing codes and the mechanics using there scanner.
Was this
answer
helpful?
Yes
No
Tuesday, December 29th, 2015 AT 1:23 PM
Tiny
KIRTIS9957
  • MEMBER
  • 10 POSTS
Update: I can remove connecters to fuel injectors 2, 4, 6, 8 and the coil pack to those four cylinders and car runs exact same! The instant I remove 1, 3, 5, 7 connecters to fuel injectors there's a instant change in running and if I remove coil pack harness to that side car cuts off. Checked fuses what would cause that one bank to misfire?
Was this
answer
helpful?
Yes
No
+2
Tuesday, December 29th, 2015 AT 2:44 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Because Cadillac has the engine off at different speeds like eway that might be what you are doing is shutting one side down to save fuel. A vacuum leak will cause what you are experiencing. It can be a h ose, gasket etc or even a cracked intake if plastic. Thee shouldn't be any difference of clearing codes but mechanics can do other stuff with their scanner which you are unable to do with yours. I would suggest them using a scope on your engine if they haven't already to see if something pops up. Also check intake vacuum at idle if it's like 15" or below it may be a plugged converter. Also check for air leaks leading to engine as well as exhaust system prior to converter.
Was this
answer
helpful?
Yes
No
Tuesday, December 29th, 2015 AT 3:13 PM
Tiny
KIRTIS9957
  • MEMBER
  • 10 POSTS
Plugged converter as in catalytic converter? I unplugged connector to coil cassette on bank 1, keyed on and got 12v. Checked ground resistance to make sure no open circut, good. When I connect it back and put in paperclip it still reads 12v. When I do the same think to bank 2 side I get 12v UNTIL I plug it back in. Then it barley shows on my analog volt meter maybe 2v. I believe its referred to as under load? What would cause that 12v to drop when connected? Snip in wire with couple strands holding on? And as far as leak notice a little smoke right by egr. Couldn't pinpoint where its coming from but kinda smells like exhaust? By the way thank you for helping been dealing with his car about a year now
Was this
answer
helpful?
Yes
No
Tuesday, December 29th, 2015 AT 3:57 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
No it's not that when it drops. Have you checked the ignition module? I think autoparts can check these. If not it may be a bad pcm. Which wold require a mechanic to install it because of security system. Also there is no code p0208
Was this
answer
helpful?
Yes
No
Tuesday, December 29th, 2015 AT 4:31 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
One other thing if you have an aftermarket alarm system installed that may be the problem. There is a tsb out on this it causes damage to converter(catalytic) as well as setting codes.
Was this
answer
helpful?
Yes
No
Tuesday, December 29th, 2015 AT 4:39 PM
Tiny
KIRTIS9957
  • MEMBER
  • 10 POSTS
Po208 or p0208 is Fuel injector open circuit
Was this
answer
helpful?
Yes
No
Tuesday, December 29th, 2015 AT 6:26 PM
Tiny
KIRTIS9957
  • MEMBER
  • 10 POSTS
Is ignition module same as coil pack? Or is it ignition control module
Was this
answer
helpful?
Yes
No
Tuesday, December 29th, 2015 AT 7:06 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Ignition control module.
Was this
answer
helpful?
Yes
No
+1
Wednesday, December 30th, 2015 AT 7:11 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
There is no 208 code it only goes to 206 for that particular problem. Try putting dielectric grease where injector harness connects to main harness.
Was this
answer
helpful?
Yes
No
Wednesday, December 30th, 2015 AT 7:18 AM
Tiny
KIRTIS9957
  • MEMBER
  • 10 POSTS
If you google p0208 there's multiple proof I mean I'm not trying to offend your experience but there's clearly a set of p0200-p0212 codes that represent circuits to fuel injector. Like p0300-p0312 is misfires. On the other hand I switched coil pack from bank one to bank two vice versa and same problem same side. And icms are mounted on coil cassettes so cant be that. Wire to bank two still dropped to 1v when I connected it so I opened harness and traced to fuse box. Checked for short or open circuit and shows its good. I'm thinking problem might be fuse box it self. Tomorrow I'm going to check volts at fuse box and if it shows 1v there its most likely fuse box but if 12v gonna be between fuse box and coil pack. Its so frustrating yet so addicting trying to find the problem! Agh
Was this
answer
helpful?
Yes
No
+1
Wednesday, December 30th, 2015 AT 6:24 PM
Tiny
KIRTIS9957
  • MEMBER
  • 10 POSTS
Oh yea and got some dielectric grease but yet to put on do to sun going down before I could finish taping harness back together. Man if that were to fix it my brain would probably explode. Lol
Was this
answer
helpful?
Yes
No
Wednesday, December 30th, 2015 AT 6:27 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
I can't think of anything else to suggest to you.
Was this
answer
helpful?
Yes
No
Thursday, December 31st, 2015 AT 5:54 AM
Tiny
KIRTIS9957
  • MEMBER
  • 10 POSTS
Me. Hmac it was the fuse box. Where the two coils splice inside of it must have been shorted. Thank you again!
Was this
answer
helpful?
Yes
No
Friday, January 1st, 2016 AT 4:57 PM

Please login or register to post a reply.

Related Engine Misfire Content

Intermittent Misfire
VIDEO
Intermittent Misfire
In­struc­tional re­pair video
Misfire Random Code P0300
GUIDE
Misfire Random Code P0300
The world of au­to­mo­tive di­ag­nos­tics can be com­plex, with nu­mer­ous codes and po­ten­tial is­sues to keep track of. One of the more com­mon en­gine di­ag­nos­tic codes is P0300, which...
VIEW MORE