Elusive cylinder 1 misfire(p0301)

**upsman72** · 03-28-2012

Ok guys let me give you a little history.My wife and i picked up a 2000 Grand Prix 3.8 gt n/a from her grand father about 6 months or so ago.It has 46k on it.He had some issues with so he dumped a whole lotta stop leak in it.(he is 97 yrs. old)Well none the less it blew the rear head gasket at #2 cylinder between the cylinder and water jacket.I tore it down and replaced head gaskets.I got it all done and now i have a cylinder #1 misfire.I started from square one.Did a compression check. 120psi across the cylinders.It draws about 15 in of steady vacuum at idle and about 19 in at mid throttle.Rock steady.So i am pretty much ruling out a intake leak,burnt valve,valve malfunction or vacuum leak and such.It's getting spark.I even swapped coils.Still getting cyl#1 misfire.So i swapped #1 and #2 injectors.Still the same.Threw a noid light on and i'm getting a strong steady pulse to the injector.I guess it could be something that malfunctioned itself but i can't help but to think it something small i missed or did.Kinda at a loss.Any ideas.Thanks

**Fivefingerdeathpunch** · 03-28-2012

Im assuming you did plugs too.

Which plugs?

Could be a bad ICM aswell.

**OH4CompG** · 03-28-2012

Is it a steady dead miss? You didn't mention spark plugs or wires. Those are two biggies to check.

**upsman72** · 03-28-2012

They are double platinum's.Can't remember brand.I can look.Forgot to mention that i did do a tune up while i was at it.New plugs and wires.I even swapped plugs and swapped wires one at a time to see if any magic would happen....nothing.

**SerenityGTO** · 03-28-2012

ew...stay away from platinum spark plugs....try a set of Autolite 104 copper plugs or some iridium plugs

**upsman72** · 03-28-2012

Would the icm still give an injector pulse even though it is bad??Becuse it is showing a strong injector pulse.

**Fivefingerdeathpunch** · 03-28-2012

Double plats are bad. A 3800 no no.

Either run AP iridums or AC delco stock replacement Iridiums.

Waste spark hates plats

**upsman72** · 03-28-2012

Would a bad icm still give an injector pulse even thought it is bad??

**Fivefingerdeathpunch** · 03-28-2012

It'll give injectors pulse if the cam and crank sensors are both working.

**upsman72** · 03-28-2012

Originally Posted by OH4CompG

Is it a steady dead miss? You didn't mention spark plugs or wires. Those are two biggies to check.

Yeah sorry,Steady miss.If you unplug the injector you really can't tell a difference.Although what's odd is if i take it for a ride and mash it it feels smooth.I guess i should mention that it seems to be only rough at idle and up to about 1300rpm.It tends to smooth out after that.Still seems to have plenty of power under acceleration.

**upsman72** · 03-28-2012

Originally Posted by Fivefingerdeathpunch

It'll give injectors pulse if the cam and crank sensors are both working.

So it could have a bad icm and still give a steady injector pulse as long as the cam and crank sensors are good??

**upsman72** · 03-28-2012

Originally Posted by Fivefingerdeathpunch

Double plats are bad. A 3800 no no.

Either run AP iridums or AC delco stock replacement Iridiums.

Waste spark hates plats

Roger that.But i doubt it would only effect one cylinder.Yes no???

**Fivefingerdeathpunch** · 03-28-2012

The ignition control module performs the following functions:

It powers the dual crankshaft position sensor internal circuits.
It supplies the voltage signals that each respective Hall effect switch pulses to ground to generate the CKP Sync and CKP 18X signal pulses.
It determines the correct ignition coil firing sequence, based on how many CKP 18X signal transitions occur during a CKP Sync pulse. This coil sequencing occurs at start-up. After the engine is running, the module remembers the sequence, and continues triggering the ignition coils in proper sequence.
It determines whether or not the crankshaft is rotating in the proper direction, and cuts off fuel delivery and spark to prevent backfiring if reverse rotation is detected.
It sends the 3X reference and 18X reference signals to the PCM. The PCM determines engine RPM from these signal. These signals used by the PCM to determine crankshaft speed for Ignition Control (IC) spark advance calculations. The falling edge of each 3X reference and 18X reference signal pulse occurs at a specific time in relation to top dead center of any cylinder stroke. The 3X reference signal sent to the PCM by the ignition control module is an ON - OFF pulse occurring 3 times per crankshaft revolution. This is neither the CKP Sync pulse nor the 18X crankshaft position sensor pulse, but both of these are required before the ignition control module will generate the 3X reference signal. The ignition control module generates the 3X reference signal by an internal divide-by-6 circuit. This divider circuit divides the CKP 18X signal pulses by 6. The divider circuit is enabled, or ready to begin dividing, only after it receives a crankshaft position sensor CKP Sync pulse. After beginning, the divider circuit does not need the Sync pulses to continue operating. If either the CKP 18X or CKP Sync pulses are missing at start-up, the ignition control module will not generate 3X reference or 18X reference signal pulses and no fuel injector pulses will occur.

**upsman72** · 03-28-2012

Ok guys gotta run to work.Thanks for the info.Keep it coming.

**upsman72** · 03-29-2012

Ok guys.Figured it out.It was kind of sitting in the back of my brain from when i put it back together.I noticed when i torqued the head that that it seemed like 1 or 2 of the bolts took an excessive amount to get it torqued.Well it didn't seal right.I went back and did a compression check again #1 was 120psi #3 was 120psi and #5 was 180psi .I have a compression leak between the two cylinders.Hey a tleast it wasn't the rear head.Saves a bit of time.Oh well,learn from my mistake.Looks like i'll be busy on saturday.lol.Thanks again guy's.

**FordMan77** · 03-29-2012

Did you install new headbolts or re-use the factory ones? The factory headbolts are TTY bolts and are not reuseable. Must be new when heads are removed.