Hey gang. I’ve perused past threads and haven’t found one with my exact issue, though I’m betting it’s similar. Not sure this is specific to SRT-6, so putting in this forum. Here goes...

For some time, I’ve had an intermittent problem whereby the car (2005 SR-6, stock other than K&N air filter, 140K miles) misfires at WOT, or near WOT. If I pull over and **** it down, then restart, it’s usually fine.

About 6 weeks ago when temps here in MD were pushing 105°+, I started it and it was misfiring to the point of being undrivable. The first time it did it, I let it sit for 5 minutes and it started and drove fine. A few days later it did the same thing, on a very hot day, it did the same thing, but refused to run even after sitting. The next morning, when it was cooler it started and ran fine, so I moved it from the street to a parking lot. That after noon (after being I the hot sun all day), it did the same severe misfire.

It did the same thing for three days and I finally called AAA to tow it to the shop. Of course, when the truck arrived the ambient temp was lower and it started and ran fine.

During all of this, it never threw a check engine code, and since it didn’t have a code, the garage didn’t know what to do with it. I had a fuel filter and pump I had recent bought, but hadn’t installed, so I had them do that. Once done, they drove it and it did the same WOT misfire and threw codes (they did not tell me which), but after some apparent head scratching said it was “definitively” the ECU relay.

As you you might have guessed, not more than a quarter mile from the shop, I stomped it and it immediately misfired and threw codes. I had to order a new code reader (note to self: never leave your code reader in the car when you take it to a shop), so while I awaited delivery, I swapped the coils packs. I thought I made progress because after installing them, the CEL went out. But alas on a test drive, it did the same misfire.

The codes it is throwing are P0300, P0302, P0303, P0304, P0305, P0306. It has also thrown P0410 (secondary air injection), but not lately.

Testing driving it, I can rev it to redline by accelerating evenly with no issues. When the misfires occur is when I stomp it or downshift to a high rpm, as if it doesn’t like sudden jolts in revs.

As a bit of background, in adddition to the recent fuel filter, pump, EXU relay and coil packs, the crankshaft sensor was replaced about 20K ago and full tuneup with new plugs about 20K ago.

I have not pulled any plugs, but they don’t feel like the problem.

I’ve heard others have issues with the coolant temp sensor, or could it be the MAP? I could imagine the super hot temp issue being different than the WOT issue, but it feels too coincidental.

 

1. When you replaced the crank position sensor did you use a Bosch? Other brands have proven faulty.
2. Many times your symptoms are related to the camshaft position sensor; but you are not showing a P0341 code.
3. With the age and miles on your car have you replaced or refurbished the Relay Control Module (RCM)? The contacts in there get burned.

 

RCM is something I would try replacing. Possibly low voltage to the fuel pump.

 

Thanks. I misspoke in my original post. It was the RCM that was replaced by the shop in the most recent visit. The same shop also did the CPS. While they are a Mercedes-oriented shop, I can’t guarantee they used Bosch, would be worth checking.

 

You changed coils, but I'm assuming you have not changed the wiring or the plugs. You might try a simple test; using a fine spray bottle of water lightly mist the areas around the wires and plugs. Do this at night in a dark garage and start the engine. Do you see sparks, lightning, arcs in the engine compartment? Replace the wires AND the plugs.

 

Your are right. Mostly. I replaced two spark plug wires that broke when replacing the coils, but left the other ten. I’ll test them next time I’m in there.

I did did the mist test and no sparks. I have a CPS on order and will tackle it again next weekend. I doubt I’ll have time to tinker with it during the week without risking leaving myself without a car to drive. I picked up a RCM and MAP from the local pick n pull too (a whopping $10 for the pair).

Interestingly, I did the throttle reset and that cleared the check engine light. Of course, it came back on again when I push it near WOT and it started misfiring again. Had to stop, shut down, and restart to continue driving. This time it shows codes P0300, P0304, P0305 and P0306.

 

If you did not see sparks, arcs then the wires should be OK. Were the new plugs gaped to .040" and you are certain they are the correct plug. Are you sure the wires are correct from the coils to the plugs. The A and B wires should lead to their respective plugs. If they are miss matched the phase shift will be incorrect. The service manual explains this.
It seems to be related to hot days and heat; Like a contact is opening from the heat. That is why I questioned you about the crankshaft sensor being Bosch and about the RCM. You might check the connections on the PCM itself to be sure all are snug, and along that same logic change out fuse 11 in the under hood fuse box. Be sure all the connections with the air flow into the engine are tight so they are not allowing more air in when it gets warmed up. There are O rings and seals on the MAF sensor housing and the throttle body that dry out and crack. Change out the MAP as you have another and get some MAF sensor cleaner and spray it a couple times to be sure that is not fouled. Fuel pressure should remain between 50 ~ 55 psi at all times. (You said you have new fuel pump and filter. The filter is also a regulator and check valve so it is important you bought the correct replacements and not just something from say Auto Zone.) It could be an exhaust restriction. You said you "swapped" the coil packs; I'm assuming that means you replaced used for new?
I'm still hoping the new Bosch Crank Position Sensor will cure your problems as what you have said is symptomatic of a bad CPS.
After that it is beyond me. You need to monitor live data to get at the cause, and a good technician can figure it out. That may be the better road to take than just throwing parts at it.

 

@zip439, thanks for the reply. To answer you comments in order...

The plugs were changed ~20K ago by the prior shop. I’ve not pulled them yet, so can’t verify gap or brand/type.

The routing of the spark plug wires is correct. Given that it gives different error codes each time, I doubt that it is a plug or wire issue.

Regarding the heat, the misfire was so pronounced on hot days, it was undrivable, regardless of throttle position. However, the WOT throttle misfire happens at any temp.

This is an SRT6, so no MAF.

The coil packs were replaced with used Bosch units off a running engine.

I don’t have the means to check the fuel pressure, so when I’m down to that I’ll find another shop to take it to and have a pro look at it again. That said, since changing the pump and filter there has been no change in the WOT issue, so while it’s still a possibility that fuel pressure could be an issue, it seems unlikely. Stranger things have happened, I know.

It could be exhaust-related. At 140K, I could imagine the cats being restricted. Is there any way to check that in a home shop?

I’ve already gone down the route of a ‘pro’ Mercedes shop looking at it and have lost all confidence in them. Any shop that tells me they can’t do anything unless I can tell them the codes isn’t worth $10/hr, let alone the $110/hr. they charge.

 

I should also note that we’ve not had such extreme heat since it had the extreme misfire issue, so I’ve no way to verify if that part of the issue still exists.

I may just need to baby it for a few weeks to avoid popping a CEL, so I can get it through emissions, then start tackling it again. It I stay out of the throttle, it drives fine.

Thanks for all the input!

 

BMO, get a quick read from an OBD reader BEFORE you go get emissions testing done. IF there are any codes relating to emissions (even pending), you'll fail and have a short time to fix it. I had a car (OBD ready) that did not trip a CEL but did have codes (yellow light on reader) that would have failed the old SC state test. If the OBD reader was anything but green LED, it failed. Good luck!

.

 

Not only that, but the codes have to be clear for two weeks or it won’t pass, or more accurately won’t even run the test.
Because it was in the shop, I was able to get an extension until Oct, but that will be here before you know it. I thought I could baby it for a couple weeks, but I had to merge into traffic today and hit about 2/3 throttle and it started misfiring and throwing codes. Had to pull over and restart. This time it shows P0300, P0302, P0304 and P0305.

 

I agree with others, and my guess is fuel pressure. You say that you've changed out the pump and filter/regulator. It would be good to verify that you're getting proper pressure to the fuel rail. It should be around 55-58p.s.i. A long hose from the fuel rail test port to a mechanical fuel gauge taped to the windshield will allow you to check the pressure at full load. Also, perhaps at 140k miles it's time to get your injectors serviced. A good injector service provider that a few here have used is http://www.witchhunter.com

 

I would suggest that you check the rail pressure to be sure its not going lean - I had the same issue when cold due to lean out at WOT. I forget about the number but about 60# at the rail which is easy to sense on the pressure tap on the passenger side near the front of the motor. I put an A/C gauge on the fitting and watched the gauge thru the windshield as I drove. Enjoy

WDY

 

I'm a newbee but I cant resist this thread. Im an old hot rodder rom the 70's. Owned a 69 chevelle big block for many years., also a former CTS forum guy.
Three things come to mind about this misfire that could be checked if they have not already been discussed.
Spark plugs if not totally clean with cause a misfire, replace new with OEM only.
Spark plug wires can break down easily. Spray with WD 40 to prove them out. If they are old change them anyway.
A lean condition of any kind will cause a bog rather then a misfire.
The key statement I read was that is was OK until he gave it a lot of gas "jumped on it" then bang. My instincts are suggesting electrical.
Is this engine using any oil?? Hot spots from oil deposits on plugs, valves, and heads can cause a misfire
Spark timing is critical as well, check it, prove it out.
Just my too sense, dont yell at the elderly!! LOL
Best of luck,
Joe

 

(whispering) Hi Joe, all good points (except our cars don't have points) HUMOR! LOL


.

 

Today I tested the fuel pressure and it is a steady 55# up to 4000rpm (the highest it will go in Park). My lead isn’t long enough to run it out of the engine bay, so I can take it on the road with the gauge hooked up (though now that i say that, I do have an endoscope I could running under the hood). I also changed the crankshaft sensor with a new Bosch unit. The current one had been in maybe 20K miles. It is marked made in Germany, but not marked Bosch. Go figure.

After those two things, I took it for a drive and boom. Same problem. This time showing codes P0300, P0302, P0303, P0304, P0305 and P0306. Stop, shut down, restart and continue no problem.

Next up testing the spark plug wires and checking the plugs.

 

Graphite Ghost! all in good fun! POINT well taken! lol

Hopefully BMO gets it figured out.

Joe

 

Me too, joeyav!

Last evening I had time to pull just three of the plugs. I tested the wires and they look in good condition and tested @ ~2200 ohms each. The plugs (NGK TR55) look good but were gapped to 0.062. I regapped them to 0.40 and reinstalled. This is my daily, so had to get it back together.

I have new plugs and wires on order and will swap them all out when they come in.

 

[QUOTE=BMO;929592]Me too, joeyav!

Last evening I had time to pull just three of the plugs. I tested the wires and they look in good condition and tested @ ~2200 ohms each. The plugs (NGK TR55) look good but were gapped to 0.062. I regapped them to 0.40 and reinstalled. This is my daily, so had to get it back together.

I have new plugs and wires on order and will swap them all out when they come in.

BMO >> NGK TR55 is not a recommended plug for your SRT6. Should be NGK plug # IFR6D10 Laser Iridium or a compatible plug to that spec. Go to their web site and search plugs, you will find 7 listings. I do not see a TR55 listed. On their PFR6T-10G Laser Platinum plugs they show a stock number of 5542. Maybe that is what you have?? It does have the gape at .040"

 

You’re right. The NGK site has several TR55s, but the Crossfire isn’t listed as fitting any of them.

FWIW, Summit does list the TR55 as compatible with the SRT-6, though it is a basic plug. Not the best choice. I’ll be replacing them with Bosch Iridium.