03 Saturn Vue. 3.0L/auto/awd, 120k ish miles

Picked up this vehicle for cheap, because the PO had incorrectly replaced the timing belt. This resulted in very much head damage.

Long story shorter......

I replaced both heads, complete with cams and valves. Got the car to run, but I'm having some issues with misfires that are baffling me.

Car runs beautifully down the highway. Only misfires while idling at a stop light, or after idling for 15-30 seconds. Codes presenting are always some variation of the same: po300, po301/303/305. It's not very often that all of the codes show at the same time. After I clear the codes with my ScanGauge, the car runs great. If you leave the stoplight and start driving again, the car runs great. Averaging about 19-20 mpg, mixed city/highway.

Replacement parts list over the last year. (This has been a spare car for a while, has recently been pressed into DD duty because it's the only one that will hold all the car seats!) All parts were either sourced new, or from a 2003 low mile Vue that was wrecked.
--Complete head job (cams/valves/heads)
--complete timing kit
--water pump
--valve cover and intake manifold gaskets
--upper intake manifold (with injectors)
--both coils (rear bank replaced more than once)
-- plugs
--bank 1 (rear?) upstream o2 sensor
--thermostat
--ECM
--additional ground from engine to body
--CPS


Sorry for the long first post here, but I'm quickly approaching my wits end. I *need* to get this figured out, and I'm running out of options and ideas.

Thanks

Paul

 

How do the spark plugs look? And check to make sure theyre right.
also check injectors.

My redline did something similar and it was a loose spark plug.

 

Plugs all looked good, actually pretty similar in color across all 6 cylinders. This issue has happened in exactly the same manner, across 2 different sets of injectors.



I failed to mention earlier, that compression tested good (and even) across all cylinders. 180 psi +, less than 5% variation between all 6 cylinders

 

Bad ign control module? Cyl 1 3 5 all on same bank?
codes not showing all at once bc module flaking out intermittently.

guess

 

Probably a stupid suggestion, but maybe check your fuel pump pressure? Maybe it's injector pressure related?

 

I would expect that if it was fuel pressure related it would affect all injectors and therefore all cylinders equally, but I don't know if the fuel routing to the two cyl banks under the hood yield the same pressure at the injectors on each bank so it's worth a check.. the fuel pressure at the rail may be barely meeting spec at startup. Then fading.

As these were not direct injection engines, I believe if fuel pressure would have been maintained constant at the rail with a vacuum based pressure regulator and possibly a return line.

Does the vehicle have dual cats?

Have you switched coil positions to see if the misfire follows the coils?

Also, and this is an uneducated question, could the cam on that bank of cylinders have cam bearings that have too much play, allowing that cam to move around at low RPM with low timing advance?

Also, is it possible one of the cams is mistimed by one tooth such that it runs rough with lower timing advance at idle, then when accelerating and at full timing advance, the timing difference is mostly accounted for so the vehicle runs okay off idle?

Sorry for the rambling unsubstantiated postulations.

There are only a few things 9ut there to cause a literal misfire.
1). )Plug firing at the wrong time when there is not enough compression.... Timing issue ( valves not closing on time --->> cam issue
2 )T cfine but plugs fouled
3) air/fuel mix wrong

Did you replace the valve guides on all of the valves replace all of thec valves? Which ones were damaged when you bought the vehicle?

 

Gonna try and get all of this answered at once:

Rear coil has been replaced multiple times. No improvement. Cannot swap between front and back banks to help with diagnosis.

Vehicle does have 3 cats, I believe. One for each bank, and a downstream after the exhaust comes together.

Cam timing is possibly an issue, although I don't really want to tear that far into it again. My issue is with that is that the misfire is not on all cylinders all the time. Sometimes it's on 3/5, sometimes 1/3, sometimes 1/3/5. If a cam was out of time, I would expect all 3 cylinders to behave the same.

Heads were rebuilt by a place in FL. New valves/guides, cams/bearings.


​​​​​​The fact is that not all 3 cylinders miss together, and that it *only* misbehaves after about 30 seconds of idle time. (The other day, I *did* notice a change in the way the idle sounded when the car flipped to "closed loop". There was a distinct change in sound, but not CEL or obvious misfire. More of a diesel-y loping sound). These 2 things are what baffle me the most.

 

Lets try this answer again, my smart phone was apparently not too smart the other day.

The heads were loaded fresh reman units. Came completely rebuilt, complete with new cams, bearings, valves, and valve guides.

The coils are not interchangeable between banks, unfortunately. However, the rear coil has been replaced multiple times, including with a known good one. This has not seemed to affect the problem at all.

I think this vehicle has 3 cats. 1 just off each manifold, and a 3rd where the pipes come together. Rear upstream o2 sensor has been replaced, as the scanner wasn't seeing any life from it.

I suppose the fuel pressure question and mis-timed cam are both possibilities, but the issue is that the cylinders on the back bank are not all missing at the same time. Sometimes it's coding for 1/3, sometimes for 3/5, and sometimes for 1/3/5. This is the most confusing issue for me, as I would imagine that a cam being out of time would make all the cylinders misfire at the same time. This random-ness is the most confusing issue for me.

 

Thank you for the detailed response.

Are you positive the rear bank is bank 1 with one three and five on it? I'm not saying it isn't. I'm simply checking. You have the literature on it I assume. Again, not challenging you just a sanity check.

I don't know how that engine detects misfires. I doubt it is like the S cars which I know the best.

I'm thinking that it is possible that the PCM is not necessarily catching all three of the cylinders with regards to misfiring. From your response, it always seems to catch two of the three and sometimes all three..

Kind of the opposite of having 4 codes for 3 misfiring cylinders where you get a p0300 random misfire along with three cylinder specific misfires which pretty much means the misfire is not random but you get that code anyway because of how it is detected.

Hook up your scanner or code reader and after the car starts, immediately read the codes. Do so as many times as you can in a row. The idea is to find when in time do you start getting pending misfire codes. They will usually have letter p after the last digit. This should allow you to determine if the misfire is starting prior to closed-loop operation.

How does the exhaust sound? Is it a smooth sound with even notes or can you actually hear the misses?

I can't remember if you have a scanner that can look at different pids. I don't remember which mode it is in but if the PCM supports it, you can look at things like number of misfires by cylinder, number of misfires since MIL last cleared.

You should also be able to look at the timing or timing advance depending on how it is expressed.

​​​​​​Try watching that in real time from startup to closed-loop and see what is going on.

Given the flakiness of it, I am still leaning towards something to do with ignition control module. Unfortunately I really don't know the details of this engine and how ignition is controlled

it could also be an issue that is heat sensitive meaning a sensor may not act up until it gets warm. Maybe get the car into closed loop. Let it run for 2 minutes. Then shut it off and monitor the temp gauge on the dash until it is significantly cooled off. Then restart the engine and see if it is running rough and if it is still in closed-loop.

Hopefully Andy will stop by, they used this 3.0 v6 in the L series cars in which he is an expert.

 

I've looked at the PCM thru a fancy shop-grade scanner. It's been a while, but this issue has been with me for quite a while now. (While I drive it to work (mostly highway), it behaves perfectly fine. Now that the wifey has it, it's stuck in traffic all day, and very unhappy.) IIRC, the scanner would register misses on cylinder #3 almost twice as fast as #1 or #5.

I can hear the exhaust and idle change, as i watch my scanner change from open to closed loop (about 100* coolant temp). The engine vibration also gets noticeably (visually) rougher. Even with this rougher sound, the CEL does not *always* register a code that I can see right away.

The fact that I can see and hear a difference in idling at the time that it goes to closed loop makes me question a sensor. Could this be cam sensor? Coolant temp sensor? (scanner reports temp about 185-190 while cruising. OEM tstat. Gauge only reads slightly above 1/4) Another o2 sensor? IAC or TB? MAF?

I will try and get it on the scanner again this evening. Playing around with the different readouts is how I found a dead o2 sensor that wasn't throwing a code, maybe i'll get lucky again.