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EDIT: I found this to be a vacuum leak, but I am still having issues, see my next post in this thread.
Hello all,
First let me start off by saying that this post will probably be long winded. But I would REALLY like to hear your opinions, so if you can bear through all the text, I would really appreciate it! I will put all of the evidence I gathered in bold so you can easily thumb through it.
I just finished replacing the cylinder heads on a 2000 Chrysler 300M. The reason why I did this was because it failed a leak down test spectacularly and was also leaking coolant into the combustion chambers. Any who, I replaced the heads and upon starting it up, the car revs and stays around 3000 RPM.
So the first thing I did was check the fuel trim levels. The STFT levels were between -11% and -15% and were steady. This told me the computer is taking away fuel.
Just to be sure of my work and the junkyard heads I got for this job, I did a leak down test. The new heads passed the test, which tells me the engine is in good mechanical condition now with the new heads. But in case you want to see, here are my results.
[b]Cylinder #1: 16% Leakage
Cylinder #2: 15% Leakage
Cylinder #3: 16% Leakage
Cylinder #4: 19% Leakage
Cylinder #5: 16% Leakage
Cylinder #6: 16% Leakage[/b]Also, when I was doing the job, I noticed the bank 1 exhaust manifold was cracked. I tried to weld it but it cracked again right away. I just left it like that because there was never any huge noticeable exhaust leak.
This got me thinking that this could be messing up the O2 sensors. I looked at the graphs of the STFT exhaust manifold sensors and bank 2 sensor was oscillating a little erratically, but it was still oscillating. The bank 1 sensor was oscillating normally.
I THEN looked at the intake air sensor reading on the scan tool. It was saying the intake air temp was over 90 degrees (it was 76 degrees outside). I am really leaning towards this being the issue, but I am not sure if an intake air sensor could cause a problem this severe.
My guess is that the computer is thinking the air is a lot hotter than it is, so it is taking away fuel (since fuel burns more easily when its hot out, and not as easy when its cold) which is simulating a vacuum leak and causing the engine to rev. I think the sensor may have been damaged when the upper intake was stored on its side upon removal and the oil inside the intake covered the sensor (it had a bad PCV)
Anyways, wanting to know what you guys think.
EDIT:
Forgot to add that the TPS reading at idle is 10.2%. Seems a little high to me. But it stays 10.2% even when I remove the throttle and cruise control cable. It maxes out at 72.6% and the voltage plot is smooth when slowly pushing up and down the pedal.
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Whatever the amount of fuel the computer injects, the rpm is still controlled by the throttle or some air bypass around the throttle.
I checked again for vacuum leaks and this time I found one around the upper intake manifold. I removed the intake and retorqued it to spec and in sequence and it does the same thing. It even has a new gasket. The lower intake that it is attached to has even been resurfaced by a machine shop. I had this done after I used a razor blade to clean the mating surface. I did this as a precaution to avoid something like this. Due to my mistake. I also checked the intake for cracks and found nothing.
There should be a hole in front of the throttle plate. What happens when you block it with your finger?
I will check tomorrow and get back to you.
Let me add that what I meant by “vacuum leak around the upper intake manifold” was “leak between the upper and lower intakes.” More specifically, toward the back. Wrote that post on my phone and wasn’t sure if it was clear.
Anywho, Ill check it out more tomorrow.
Yeah, just wondering if you IAC is sitting wide open. If it is it maybe could produce an idle that high.
This is interesting
I have installed the wrong head (I.E. one for a 5SFE on a 3SFE)… They were identical except one thing… An air assist that ran from the throttle body to the head. Engine idled high and had negative fuel trims… took about an hour for me to find the issue.
Also, Coolant can cause issues with O2 sensors… I hate to throw O2 sensors under the bus so quickly but perhaps there may be something there…. If this car had a coolant leak, it could have screwed up the upstream sensor…
What is the position of the throttle plate? (and throttle linkage) If it has it… Perhaps back off the throttle wire adjustment (have seen this give high idle)… perhaps someone adjusted the wire before you had it…
Are the heads the exact proper ones for the job… O2 sensors? Just some things to think about…
All the best
-Karl
[quote=”ToyotaKarl” post=107255]This is interesting
I have installed the wrong head (I.E. one for a 5SFE on a 3SFE)… They were identical except one thing… An air assist that ran from the throttle body to the head. Engine idled high and had negative fuel trims… took about an hour for me to find the issue.
Also, Coolant can cause issues with O2 sensors… I hate to throw O2 sensors under the bus so quickly but perhaps there may be something there…. If this car had a coolant leak, it could have screwed up the upstream sensor…
What is the position of the throttle plate? (and throttle linkage) If it has it… Perhaps back off the throttle wire adjustment (have seen this give high idle)… perhaps someone adjusted the wire before you had it…
Are the heads the exact proper ones for the job… O2 sensors? Just some things to think about…
All the best
-Karl[/quote]
Thanks for your response ToyotaKarl.
To me, the heads seemed identical. This car has the 3.5L and everything seemed to have a place, didn’t see any connection that wasn’t used on the head. I am not sure this is the issue (thank god!) because upon second guessing myself, I found a vacuum leak between the upper and lower intake mating surfaces. I cannot seem to get it to go away (as mentioned in my previous posts) which is leaving me stumped!
The throttle plate says it is open 10.2% at idle. It has linkage, but even after I REMOVE the cables, the TPS still says 10.2%, meaning adjustment isn’t causing that number, and the engine still does the same thing.
How have you determined you have a vacuum leak between the upper and lower intake mating surfaces?
If so, how big…
Also have you put a Vacuum gauge on the engine? Tested it at Idle, light throttle, medium throttle and WOT?
3k RPM is pretty high to blame a simple vacuum leak IMHO and a vacuum leak should cause positive fuel trim numbers… You are dealing with a rich condition…
Think you may be chasing a “small” red herring right now…
-Karl
[quote=”ToyotaKarl” post=107262]How have you determined you have a vacuum leak between the upper and lower intake mating surfaces?
If so, how big…
Also have you put a Vacuum gauge on the engine? Tested it at Idle, light throttle, medium throttle and WOT?
3k RPM is pretty high to blame a simple vacuum leak IMHO and a vacuum leak should cause positive fuel trim numbers… You are dealing with a rich condition…
Think you may be chasing a “small” red herring right now…
-Karl[/quote]
I noticed that when I spray throttle body cleaner between the upper and lower intakes in a certain spot, the RPM goes down. I can also hear a loud “HISSSSSS” around the same location when the engine is running. A vacuum gauge is a good idea, I will do it tomorrow and post back with the results.
I believe the fuel trims may be caused by a bad IAT sensor. I noticed that when I had my scan tool hooked up, it was saying the intake air temperature was 91 degrees when the outside temp was 74. I checked it again 30 minutes later and it was up to 97. My guess is that the computer thinks the intake air is real hot, so it takes away fuel. This accounts for the negative fuel trim values. (I am assuming that fuel combusts easier when its hot, just like it is hard to combust when its cold outside.) This is just me guessing though.
[quote=”Xyius” post=107263][quote=”ToyotaKarl” post=107262]How have you determined you have a vacuum leak between the upper and lower intake mating surfaces?
If so, how big…
Also have you put a Vacuum gauge on the engine? Tested it at Idle, light throttle, medium throttle and WOT?
3k RPM is pretty high to blame a simple vacuum leak IMHO and a vacuum leak should cause positive fuel trim numbers… You are dealing with a rich condition…
Think you may be chasing a “small” red herring right now…
-Karl[/quote]
I noticed that when I spray throttle body cleaner between the upper and lower intakes in a certain spot, the RPM goes down. I can also hear a loud “HISSSSSS” around the same location when the engine is running. A vacuum gauge is a good idea, I will do it tomorrow and post back with the results.
I believe the fuel trims may be caused by a bad IAT sensor. I noticed that when I had my scan tool hooked up, it was saying the intake air temperature was 91 degrees when the outside temp was 74. I checked it again 30 minutes later and it was up to 97. My guess is that the computer thinks the intake air is real hot, so it takes away fuel. This accounts for the negative fuel trim values. (I am assuming that fuel combusts easier when its hot, just like it is hard to combust when its cold outside.) This is just me guessing though.[/quote]
I don’t think your IAT is malfunctioning that bad… While they are usually not supposed to be over/under 10-15% of the ambient air temp, it is not uncommon for the engine bay to get warmer than Ambient Air temperature. (think of you working on your car and standing in front of the car, now put your face close to a warm engine…It is hotter down there)..
IAT temperature will be warmer on a standing car with a running/warm engine… Here is a good test… Check to see if the IAT generally matches the ECT with a scanner (without starting it) tomorrow morning… If it is off more than 10-15% then MAYBE.. but I don’t think that is it…
I really believe that you do have a vacuum leak, but I also really question two things…
1. The fact your engine is receiving too much fuel… Why? That IMHO is the Million dollar question…
2. The performance of your upstream O2 sensors…. I suggest watching them on the scanner… How fast are they switching…
One last thing… Check for pending codes…
JMHO
-Karl
Couple of things to add on… You say the RPMs go down when you blast it with throttle body cleaner?
Also, here is one thing I learned about that F@#$(%$ 3.5 engine… Which may or may not apply… A hiss can be at the intake’s EGR tube… Those things have small “engine-ingestible” gaskets… They go bad or get out of position, or ingested all the time when the intake is removed/replaced… Chrysler techs hate to deal with them… This is the tube that points directly towards the firewall and simply “plugs into” the metal EGR tube which may lead to the passenger EGR assembly….
I believe you are moving in the right direction (fix the known problems… I.E. hiss or vacuum leak) and then see what happens…
All the best…
-Karl
Yes RPM’s go DOWN.
During the head replacement I had to remove the EGR valve with tubes attached. The tubes went from the valve and plugged into the bottom of the intake where they are fastened by a retaining clip. If I recall, they were sealed with O-rings.
These tubes are actually really close to where I was spraying the TB cleaner. Perhaps I was mistaken in where the source of the vacuum leak was coming from. I will have to double check tomorrow. Man, this list of “things I will do tomorrow” is really growing!
They must have improved the EGR system… As I said… It may apply (but possibly does not)…
I know you will find the problem… Hope to hear from you tomorrow evening with good news! 🙂
-Karl
I found the problem!
Turns out it WAS the EGR pipes that were leaking. Apparently in the process of replacing the heads, the orings that sealed them must have fallen off. I ordered generic ones from pepboys and now my idle is fine! However, they do not seal 100% because they aren’t thick enough. I will need to order the factory replacement ones from Mopar.
Thanks a lot Karl!
Additional Notes:
-The IAT reading and ECT reading were almost identical in the morning.
-The engine has 21 inHg, telling me the intake gaskets are fine.
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