Engine misfire

[Potto1991]

My Bonneville is running rough and has two codes p0304 come up twice I have change intake gasket,sparkplugs, spark plugs wores, and swapped injectors what could be causeing misfire?

[96 SSEi]

hi, it seems you have a misfire on cylinder #4 .please pull the plug and inspect for damage - make sure gap is correct - I think its .060inch - make sure wires are not damaged and is connected firmly on both ends

the bank of cylinders near rad is 1/3/5 and the one near firewall is 2/4/6 so #4 is centre cylinder on back bank - check it and check coil for that cylinder - post back with results on wire/plug and contacts condition please

[Potto1991]

i forgot to say that it overheated it was a hole in raidator fixed that and then this problem came up i have put new spark plugs and new wires in. when i pull spark plug on number 4 out its wet and smells like gas

[96 SSEi]

i forgot to say that it overheated it was a hole in raidator fixed that and then this problem came up i have put new spark plugs and new wires in. when i pull spark plug on number 4 out its wet and smells like gas

ok, that would explain your misfire code - now to find why it is not firing
with rubber glove or rubber gripped pliers, hold wire with plug inside over the front strut mounting bolt on top of strut tower
get some one to crank engine and see if you get spark from it, if no, use another plug - if still no, remove wire from coil and coil will arc when you crank - remove fuel pump fuse so car wont start

if no spark from coil, you have to diagnose no spark condition on #4.........post back with your findings......later

[Potto1991]

so i take out the plug and hold it over the bolt with the wire attached

[Potto1991]

when i put the wire over the bolt i get a spark

[96 SSEi]

ok, good.So you got spark on 4. can you please tell us more about the swaping injectors story....why, what for....thanks

[Potto1991]

i swapped injectors because i was readings that it could cause the misfire in gm cars so what else could cause the misfire when i clear the codes the car will run good for a few minutes then will run rough and check engine will blink the i check codes and get p0304

[96 SSEi]

so when you got spark from the wire to strut nut, did you have the plug on the wire? - if not, see if spark comes from plug to strut nut
.............later

oh, when you do these spark tests, it is important not to touch the metal of the car with any part of your body - don't want you to zap your pecker....lol

[96 SSEi]

i swapped injectors because i was readings that it could cause the misfire in gm cars so what else could cause the misfire when i clear the codes the car will run good for a few minutes then will run rough and check engine will blink the i check codes and get p0304

you can get more info on misfires here...........http://troubleshootmyvehicle.com/gm/3.8 ... re-codes-1

save to fav/bookmarks.........it's gold!!

[MKMike]

The link that 96 SSEi posted is excellent and has all the info you need.

Since you overheated the car, you may have blown out a gasket--depending on how badly it overheated.
A compression test will rule that out or confirm it.
If compression is low in that cylinder then you warped the head or damaged the head gasket when it overheated---or there were ring/valve issues that coincidentally occurred around that time.

You might have a bad coil that is putting out a weak spark or even a failing ICM that causes a weak/absent spark as it warms up.
The presence of a spark isn't enough--it has to be strong enough to jump the plug gap
You may have a massive vacuum leak at that cylinder. Leaks occur at the intake manifold gasket, injector 0 rings and vacuum hoses .
Vacuum hoses have a nasty habit of breaking/cracking on the underside where you can't see.
Some use carburetor cleaner or metered propane to find vacuum leaks.

A few simple things to check besides compression:
Make sure that the #4 wire is not so close to any metal that the spark arcs there, instead of power getting to the plug.
Are the spark plugs properly gapped? What brand plugs are they?

Swap the 1- 4 coil with another and see if the problem moves with it.

If it moves, then the 1-4 coil is the problem.

If the problem remains at cylinder #4, then you have either: power absent from injector (unlikely, since the plug is gas fouled), a failing ICM--that isn't always sending the power to the coil when #4 should fire, or poor compression. (Assuming you don't have a defective spark plug or wire. Bosch plugs, for whatever reason, often fail to fire in the 3800.)

All possibilities are summed up in Willwren's post here http://www.pontiacbonnevilleclub.com/fo ... c4184.html
and 96SSEI posted a link to step by step diagnostics to follow.

Hope you'll let us know what you find.

[SATADrive420]

I don't seem to have any problems with the bosch plugs in my bonneville, they've been running strong since 2006.

[MKMike]

I don't seem to have any problems with the bosch plugs in my bonneville, they've been running strong since 2006.

.....and people sometimes step into a roadway without looking and don't get hit by a car or truck.

Just lucky.

Having had experience with Bosch spark plugs many years ago, both as a mechanic and before owning a Bonneville, I would never consider installing them in an engine again.

I'll start with the PontiacBonnevilleclub's very own Tech info database

http://www.pontiacbonnevilleclub.com/fo ... 40156.html Note what it states about Bosch spark plugs, wires and oxygen sensors


Next up http://www.pontiacbonnevilleclub.com/fo ... ilit=bosch pay attention to crash93ssei and SSEBonne4evr


Then we move to http://www.pontiacbonnevilleclub.com/fo ... 39853.html

and

http://www.pontiacbonnevilleclub.com/fo ... 20516.html


http://www.pontiacbonnevilleclub.com/fo ... ch#p449704 post by 94SilverSSEi


http://www.pontiacbonnevilleclub.com/fo ... ch#p430835 Jrs3800


http://www.pontiacbonnevilleclub.com/fo ... ch#p421904 nos4blood70

Do a forum search just using the word Bosch and you'll find pages of complaints like these.

[Potto1991]

Ok update cylinder 4 compression test was 60 and all other cylinders was 120 so I have a blown head gasket? I think it's a small leak that puts oil in my coolant so I bought a bottle of blue devil sealer to see if that would work so when I start it no it doesn't misfire it did have a code p0108 come up but I just replaced map sensor but it's still running rough

[96 SSEi]

hey, please check the wires and connector of the MAP for damage and be sure its seated properly. also check for vacuum leak in that area
There is a way to test the voltage to pcm but I dont know the proper volt readings - someone i'm sure knows and will post them.

[Potto1991]

I'm not having a map issue any more it's just running rough and overheating then when I turn heater on its drops back down

[96 SSEi]

I'm not having a map issue any more it's just running rough and overheating then when I turn heater on its drops back down

ok, what temp are you seeing on the temp gauge? do the fans turn on when it gets hot?

to check if fans are working, unplug the coolant temp sender right below the thermostat- the temp gauge wont work but the fans should come on high speed on both.

[Potto1991]

so i have one cylinder with low compression and i have oil going into my coolant my question is is it a intake manifold gasket or is it my head gasket?

[96 SSEi]

it could be both: did you follow the instructions when using the blue devil stuff - if you dont get engine up to temp, it wont seal properly.

[Potto1991]

how could i figure out which it is