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Discussion Starter · #1 · (Edited)
(Skip to Double Space for facts & data, actual questions are at the bottom) Hello all, I’m a young technician about 6 months into my own shop business and have been ALL over these forums the past week, as I have a customer with a 2008 CTS who was having major performance problems. Cyl. 2, 4, and 6 were dead, on a test drive, she locked up on me and wouldn’t start again. Cam/crank correlations and some research gave away the timing chains. I could almost skip the cam teeth by hand with only the valve covers off. Interference engine. Lovely. Pulled heads, checked valves. FILTHY. They wouldn’t seat at all, but none were visibly bent.

Rebuilt the heads, new oil pump, water pump, timing kit, intake and exhaust valves and seals, and spark plugs. I advised the customer to go ahead and replace the disgusting injectors while they were easily accessible (and all the one time use components).
Started up, sounded gut wrenching for 15 - 20 seconds. Evened out over the next hour with a few key cycles while monitoring data but was still making a lot of top engine noise. I’ve read everything I can find online about these engines. I know the HPFP and injectors make noise. Stethoscope sounded like middle of Bank 2. Pulled both valve covers and checked all lash adjusters and rocker arms, everything looks fine, normal wear, nothing terrible. Also pushed gently on injector connectors to ensure that they are fully seated.
It continued to idle too rough for my liking dead on at 550 (desired idle speed was within 15 RPM throughout).
Few revs and audible misfires on deceleration. I was hesitant to put it on the road because I didn’t want to ruin the cats. Cyl. #3 & #6. The scanner misfire counter counted 3 & 6 almost identically. Didn’t count any misfires at idle, but still very rough. Not full combustion on all cylinders for sure. Later noticed 3 started counting misfires at about 1000 RPM, and 6 started counting at 1500 RPM, but they still stayed no more than 2 counts different from one another.
Switched 3 & 5 coils and 6 & 4 coils. Misfires didn’t follow coils. Tested coil resistance, all very similar. Tested spark with an inline spark tester, nothing unusual. Did same swaps with plugs. Misfire didn’t follow, but they looked a little dry fouled. Gaps were also double checked and were at around .033” give or take. Carefully gapped to spec. Engine took much less time to idle down to 500. Still nasty rough. Checked oil level, good oil pressure, ok let’s test cylinder compression. I was actually impressed here. 200-215 across the board. The minimum spec is 140 PSI. Ok, got compression. Checked wire harness continuity from PCM connector. Several wiggle tests showed no failure on either ignition coil circuit. Also tested resistance between PCM and coil connectors. 0.00 ohms. Codes are p0300, P0303, P0306. Nothing else.
I’ve read injector faults will throw P020x. None of that. Bank 1 STFT at idle stays about twice as negative as Bank 2. I really don’t wanna pull the injectors and replace all the one time use parts again, and don’t have any data that points to injectors. Pulse widths on the problem cylinders are a bit shorter than the others, no surprise. I’m sure it’s trying to protect cats. A full 2 days of research and hopeless testing have left me with nothing but frustration and less hair.
I decided to put it on the road to get done miles on it in case the PCM needed more drive info to make proper adjustments. Cleaned MAF and TB, reset idle learn, checked for vacuum leaks, and hit the road. DAMN that thing flew. But the blinking CEL followed every hard pull.
I’ve seen some mention of PCM failure in cases like this, but man. I don’t throw parts at cars. If I can’t verify the failing component, I won’t even accept a diagnostic fee.
It did get less severe after driving about 50 miles. But it hasn’t been resolved. And sometimes runs so smooth it feels like it stalls, then right back to rattling the exhaust off.

So here’s what I’m looking for. Is there a known way to verify PCM failure? Is there a possibility of a failing new injector without injector error data? Is there a safe way to discharge an injector through the PCM harness (not enough room between rails to get to injector pins)? I’d like to discharge all cylinders and monitor pressure drop. Spec is 3 PSI drop. My scanner can command injectors on any other GM it’s talked to except this one.
Sorry for the long read, I just want to give y’all full situational info to avoid some unnecessary back and forth.
 

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2010 CTS4 sedan
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Have you monitored the signals from the upstream O2 sensors? That shouldn't cause misfires but given the mess you've described, I suspect those sensors are toast - and that cannot help.

Also, what does the fuel rail pressure look like at idle and WOT?

Good luck - you definitely are chasing ghosts but you've already caught a few.
 

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Thorough first post. Refreshing.

Vehicle mileage, breakdown of components in chain "kit" and brand of timing, ignition, and injector parts may prove helpful.
 

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08 CTS DI
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This motor is petty and very sensitive to small deviations from the norm. What is the condition of the fuel in the tank and is it possible you mixed up the camshafts (swapped positions) during the cylinder head rebuild, there is a TSB addressing this issue as an inexplicable misfire, particularly on remanufactured motors, which would also include remanufactured cylinder heads which likely replaced the heads deemed to have porosity caused oil leaks into the spark plug tubes.

Aside from that, the usual causes such as small air leaks. The info Long pointed to will be helpful for more ideas.

The first generation CTS was noted for misfiring associated with failed PCMs, I do not recall such an issue with the second gen which uses a different PCM in all of the reading I've done.
 

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Discussion Starter · #6 · (Edited)
Have you monitored the signals from the upstream O2 sensors? That shouldn't cause misfires but given the mess you've described, I suspect those sensors are toast - and that cannot help.

Also, what does the fuel rail pressure look like at idle and WOT?

Good luck - you definitely are chasing ghosts but you've already caught a few.
The upstreams were flipping from rich to lean as expected, but one of the down streams was keeping pretty low. Around 100-200 mV. It may not have been warm enough when I was checking, but the other downstream seamed to hang out where it should, about 650 mV. Fuel pressure at the rail at idle hovered from 520 PSI to about 620 PSI. I will test at WOT today.
 

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Discussion Starter · #7 ·
Thorough first post. Refreshing.

Vehicle mileage, breakdown of components in chain "kit" and brand of timing, ignition, and injector parts may prove helpful.
Mileage is around 130k I think. I’ll check today. Chains, sprockets, tensioners, guides, oil pump, and water pump came in the timing kit. Injectors were an eBay purchase, I believe. Customer provided parts, and I did remind him that I can’t warranty parts I didn’t source. I know how GM is about AC Delco sometimes, but I’ve also heard some say that’s not exactly the case anymore. Although I did purchase AC Delco rapid fire plugs. The coils were all stock except for one, and that cylinder gave me no trouble.
 

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Discussion Starter · #9 · (Edited)
This motor is petty and very sensitive to small deviations from the norm. What is the condition of the fuel in the tank and is it possible you mixed up the camshafts (swapped positions) during the cylinder head rebuild, there is a TSB addressing this issue as an inexplicable misfire, particularly on remanufactured motors, which would also include remanufactured cylinder heads which likely replaced the heads deemed to have porosity caused oil leaks into the spark plug tubes.

Aside from that, the usual causes such as small air leaks. The info Long pointed to will be helpful for more ideas.

The first generation CTS was noted for misfiring associated with failed PCMs, I do not recall such an issue with the second gen which uses a different PCM in all of the reading I've done.
Everything on the heads went back where they came from down to the lash adjusters. I was very careful to ensure that was the case. I tested the phasers for play, found none. But with how dirty bank 1 was under the valve cover I could have thrown all 4 cams in the trunk and I could still tell which was which. I went wild and bought the $5 camshaft retainers to help with timing accuracy too. Can’t afford to be careless 😂 No oil in plug tubes, but I will search for that TSB. I went through a few of them but man, there are a bunch on this model. The only “known” about the fuel in the tank is that it’s 87. Which I’ve read these cars are programmed to run fine on. But they are definitely picky about a lot so 🤷🏼‍♂️ I ran injector cleaner through the tank, read a post that said that last Hail Mary attempt actually solved another PITA misfire condition. Worth a shot, cheap, no labor. I’ve also advised the customer to send his old OEM injectors to be rebuilt rather than buy new OEM injectors if the problem can be narrowed down to the injectors. Then I’ll just have to wrestle with replacing them with the heads installed.
 

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Discussion Starter · #10 · (Edited)
Also guys, seriously. Thank you for y’all’s time. I’ve posted on other forums with problems on my daily driver and some of those posts are years old now with not a single reply. I really appreciate the quick and well informed interaction. You guys are so smart! 😁
 

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2011 CTS Coupe Premium
Orlando - We take orphans
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Agree ACDelco is not what it used to be, GM has gotten very big in China. "AC Delco rapid fire plugs" Rapid Fires (late platinum not early copper so much) are good but any more I prefer iridium.

Also did you do a leakdown test ? I find them more informative than a compression test.
Been meaning to build adapters for my old ignition scope, have never found anything that would tell as much as watching waveforms but was a lot easier with a distributor.
 

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Discussion Starter · #13 ·
Agree ACDelco is not what it used to be, GM has gotten very big in China. "AC Delco rapid fire plugs" Rapid Fires (late platinum not early copper so much) are good but any more I prefer iridium.

Also did you do a leakdown test ? I find them more informative than a compression test.
Been meaning to build adapters for my old ignition scope, have never found anything that would tell as much as watching waveforms but was a lot easier with a distributor.
I believe I installed ACD #6 plugs. I’ll have to check and see what the base metal is. I haven’t done a leak down test, and don’t have the tools for that, although this is how I’ve been building my tool collection. Need a tool? Cool I’ll go buy it. Then I’ll have it. It’s hard to do that sometimes with an infant business and trash credit 🙄 I’ll pick up iridiums and install today. I’ve pulled the coils, plugs, and intake on this thing so many times, I could install new plugs all the way around in about 5 minutes. Yippee.
 

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2009 CTS 3.6L DI rebuilt to FE3 J55 G80 3.42:1
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It is not unusual for a new valve job to require some run time for the re-ground valves and seats to seal to each other. Sounds a bit odd, but I have seen it before.
 

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Everything on the heads went back where they came from down to the lash adjusters. I was very careful to ensure that was the case. I tested the phasers for play, found none. But with how dirty bank 1 was under the valve cover I could have thrown all 4 cams in the trunk and I could still tell which was which. I went wild and bought the $5 camshaft retainers to help with timing accuracy too. Can’t afford to be careless 😂 No oil in plug tubes, but I will search for that TSB. I went through a few of them but man, there are a bunch on this model. The only “known” about the fuel in the tank is that it’s 87. Which I’ve read these cars are programmed to run fine on. But they are definitely picky about a lot so 🤷🏼‍♂️ I ran injector cleaner through the tank, read a post that said that last Hail Mary attempt actually solved another PITA misfire condition. Worth a shot, cheap, no labor. I’ve also advised the customer to send his old OEM injectors to be rebuilt rather than buy new OEM injectors if the problem can be narrowed down to the injectors. Then I’ll just have to wrestle with replacing them with the heads installed.
Yes it's programmed to accommodate regular unleaded, but I have first hand experience in the fact that it is also programmed to respond to higher octane fuel with increased spark advance. It also helps tremendously with engines that are a bit fussy on cold starts that tend to pop and reverse into the intake.

Injectors were an eBay purchase, I believe. Customer provided parts,
Find out what the quality of the injectors are. If they were really cheap they may be the problem, especially with that low downstream O2 reading. My readings on both banks are around 600-700 mV. I purchased my injectors on ebay, but they were refurbished originals from a company that had been in business offering the service for a while.

Here is a link to the bulletin I mentioned.
Remanufactured V6 Engine Misfire – TechLink
 

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Discussion Starter · #18 ·
Yes it's programmed to accommodate regular unleaded, but I have first hand experience in the fact that it is also programmed to respond to higher octane fuel with increased spark advance. It also helps tremendously with engines that are a bit fussy on cold starts that tend to pop and reverse into the intake.



Find out what the quality of the injectors are. If they were really cheap they may be the problem, especially with that low downstream O2 reading. My readings on both banks are around 600-700 mV. I purchased my injectors on ebay, but they were refurbished originals from a company that had been in business offering the service for a while.

Here is a link to the bulletin I mentioned.
Remanufactured V6 Engine Misfire – TechLink
Im looking at normal down stream readings now, but it shows upstream fuel trim goes from closed to open loopevery now and then on the road.
 

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Discussion Starter · #19 ·
UPDATE!!! UNUSUAL KNOCK SENSOR ACTIVITY??? Knock sensor 1 reference and signal are reading 6-50v fluctuating often while driving. Bank 2 same patterns but +20% voltage. The range listed is 0-5v soooo what the hell. I’d like to learn about these guys and what I’d normally see here.
 

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UPDATE!!! UNUSUAL KNOCK SENSOR ACTIVITY??? Knock sensor 1 reference and signal are reading 6-50v fluctuating often while driving. Bank 2 same patterns but +20% voltage. The range listed is 0-5v soooo what the hell. I’d like to learn about these guys and what I’d normally see here.
This motor also has a history of spark knock under circumstances where it shouldn't, discovered in the Camaro tuning community. I was not able to completely eliminate it with 100 octane fuel (premium plus octane boost). Datalogging is how I know it takes advantage of increased octane fuel, and since it does not have a sensor to estimate fuel quality, it probably uses the old method used for testing the knock detection system by deliberately advancing ignition under designated conditions and noting the onset, or absence of spark knock. The only way the Camaro enthusiasts were able to clean up what was eventually called false knock, was to adjust the sensitivity tables in the tune, otherwise it's going to show up seemingly inexplicably at times, especially on 87 octane.

Doesn't mean what you've found isn't a clue, it just seems a bit strange for it to come along out of nowhere if it wasn't already present before hand. Make sure your grounds are good, although it's unlikely you haven't addressed that.
 
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