2002 SSEI
Items checked/completed:
1-used OTC 6589 HEI spark tester, at end of each plug wire-OK
tested spark from each coil tower-OK ICM and coils appear to be working properly
2- changed all spark plugs installed new NGK TR55 @ .058"-no change in missing
3-unplugged MAF sensor with engine running--No change
4-Checked fuel pressure at rail schrader fitting 46 psi, unplugging vacuum to regulator 52 psi. pressure holds after engine shut down and is the same days later (no injector leak down)
5- only other code stored is P1639 A/C refrigerant pressure sensor voltage issue(have had this for several years)-Have changed the sensor twice..
6- Checked all vacuum lines from MAP sensor to SC snout, FP regulator and WG actuator--all ok
7-Sprayed along manifold rails with carb cleaner--no change in idle character or rpm
I don't have access to a Tech 11 so I am not sure what cylinders are misfiring...
What is next step in trouble shooting?

Are you noticing the misfire at idle or under load?

Compression test to verify you don't have a chipped piston.

Might be time to get a proper scan tool if you want to continue working on it yourself. Otherwise you'll just keep launching the parts cannon. Even the "Torque Pro" app will have misfire data. https://www.amazon.com/dp/B07Z65HX5X/

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 57k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 115k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 280k | Official Bonneville Hauler

At idle, engine shakes and sounds like it is running on 5 cylinders, when driving, roughness from engine with power lacking, not smooth at all--ESC light flashes continuously
Procedure for doing compression testing? Would a problem cylinder show on it's spark plug (visual)
Remove all spark plugs
Disable ignition system such as disconnecting the ICM?
Disable the fuel injectors--Remove fuse?
What should compression be (150 psi)?
If issue was with one cylinder with low compression, wouldn't it code one cylinder code such as a P0301, 302, 302, 304 , 305 or 306? I.E. Only one code such as P0302 if #2 cylinder was low in compression as opposed to multiple cylinder misfires (P0300).
Is there any chance of an issue with Crank PS or Cam PS?

Obtained an OBD scanner today and verified that #4 cylinder (coded as P0304) is the only cylinder misfiring..I reaffirmed that the ICM and Coils are all working and the spark plug wires all all good..Will do a compression test tomorrow on #4 cylinder and compare to the others.

Now I am in a quandary...I did a compression check and all 6 cylinders including #4 are 150 psi within 1 or 2 psi...I was very surprised..Does anyone now know where I go? After clearing the P0304 code, engines starts and runs a little rough for about 30 seconds or so and the code P0304 is set and engine service light flashes..The spark plug in #4 position looks almost like it did when I installed it a week ago , clean and I can smell gas on it..

I know you replaced the plugs, but did you replace the wires? Based on everything you've mentioned, that's what I would look into.

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 57k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 115k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 280k | Official Bonneville Hauler

I ohm'd all the spark plug wires and they all were good 1200-1800 ohms depending on length.. The OTC spark tester showed spark at the end of each spark plug wire..The #4 spark plug today still looks like it did when I installed it with no discoloration on the ground strap ,no discoloration on the plug base circular ring and very little discoloration on the porcelin. I am now thinking I may have a fuel injector issue on that cylinder (#4). I will replace that injector next with a new one.

A plug wire can ohm out OK and deliver spark to a spark tester and still be arcing out a misfire. I would have replaced the wires when you did new plugs.

You can check for injector pulse at the connector with a #194 bulb.

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 57k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 115k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 280k | Official Bonneville Hauler

I have used a noid light on the #4 injector harness connector but still could be an issue with the injector itself or may be plugged or partially plugged. I will change the #4 spark plug wire and see if there is any difference on the issue.

The fuel rail is pretty easy to pop off too if you wanted to just move the injectors around to see if the misfire follows.

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 57k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 115k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 280k | Official Bonneville Hauler

Yes, I thought about doing that but decided that if I was removing the fuel rail, I might as well replace the #4 injector. That would save me the effort of removing the rail again to replace the injector if the problem moved to another cylinder. Do you think there can be another issue within the valve train that would cause this? It does have 150 psi cylinder compression but the non coloring of the spark plug ground strap, circular base ring and porcelin is strange.

I replaced the #4 spark plug wire today and the issue is still present with #4 cylinder misfires....I did go ahead and removed the Fuel rail and cleaned the fuel rail and old injectors on their exterior, also cleaned the corresponding injector holes in the heads,, Waiting for the new fuel injector for #4 cylinder to be delivered (Wednesday). Harofreak00 what has been your experience with this problem as far as source? Any possibility of a valve train issue? Should I pull the rear valve cover?

Harofreak00 I have not changed my ICM but spark tested it from each coil tower.. Is there a possibility this #4 cylinder misfire could be caused from the ICM? I will receive the new Fuel injector tomorrow and will find out if that cures the issue...Just looking ahead in case that does not solve the misfire.

If you have 150psi compression, you have no valvetrain issues. I still think this is an ignition issue. Yes the ICM could cause no spark on #4, but that would have been present with the spark test. Let's see what the injector does.

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 57k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 115k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 280k | Official Bonneville Hauler

Thank you, This is a difficult one for me.. Good thing I own two Bonneville SSEI cars...I can normally diagnose car issues as I have done so on my muscle cars, my Grand Nationals, GTP's and SSEI's. I was driving at 55 mph when this issue first appeared with the flashing ESC and loss of power and missing and roughness...Before I start it up after the injector change, I will also put in a fresh NGK plug. Looking at the injectors, very hard to see any differences between any of them and the small orifice holes on each look not plugged..I suppose the injector could fail internally with the coil or pintle..I agree with you, this seems to be an ignition issue but hopefully it will be the injector. I was very surprised when all the cylinders were 150 psi + or - 1-2 psi.

Well just finished changing #4 injector with a new Standard FJ250 injector...Started car back up and miss fire is still present.. The Launch CR3008 Scanner says #4 cylinder misfires.. My regular scan gage in the car reads P0300 (Random missfires)..I am perplexed...Any ideas? Should I have changed the other 5 injectors? They are original (190000 miles)..2002 SSEI

Noticed while changing the #4 injector that there was a lot of oil on the back side head at the intake manifold and that I also noticed that the coolant bottle was almost empty (no leaks externally found). I checked the oil and oil level was full with no trace of coolant..clear oil on the dipstick. It is possible the intake manifold lower gasket is leaking coolant into #4 intake runner.

If it was leaking enough coolant to cause a misfire you'd have white smoke out the tailpipe. Circle back to the ignition I think

_________________
Andrew - owner/operator of Bonnevilles Unlimited

2004 Bonneville GXP | 60k | White Gold Tricoat | custom built supercharged 3800 hot rod | garage queen
1997 Corvette | 57k | Silver Metallic | Z06 wheels | Date-night Hauler/Parts runner
2014 Town & Country Limited | Cashmere Pearl | 115k | Family Hauler
2002 Ram 1500 Quad Cab Sport | Black| 280k | Official Bonneville Hauler

I think I am going back to see if #4 injector is firing.. I am going to use the Noid light on #4 injector harness connector with the engine running to see if it is flashing. This would eliminate possible harness pin issue or wire feed issue which would not fire the injector. Is it possible to still be a ICM issue for #4 cylinder (hard to believe since no issues with #1 cylinder which uses the same coil tower and both are signaled from the ICM)? Any sure fire way to trouble shoot the ICM short of replacing it which is expensive. Wouldn't coolant ingested in #4 cylinder show on the spark plug along with coolant smell? I see no contamination or discoloration or smell on #4 spark plug..if the injector was supplying fuel to #4 cylinder and the plug was not firing wouldn't it show visually on the spark plug? I would think if it was delivering fuel to #4 cylinder and the spark plug was firing, the spark plug would look similar to the other plugs which show the heat discoloration at the bend on the ground strap on the plug and on the base circle on the plug. If the plug was not firing and fuel was being delivered, wouldn't the plug be saturated with fuel and almost fouled?

I used the Noid light on #4 cylinder injector harness connector and with the engine running, the light flashes quickly.. My next step I think will be to remove the rear valve cover to inspect the valve train for #4 cylinder and it actuation and lifting and closing of bot valves to see if there is a valve lift issue from valve train or camshaft lobe issue .