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I had a 2005 Chrysler PT Cruise 2.4 come in yesterday with a P0300. I checked vacuum, it's sitting at about 19". Our shop put new plugs and wires on it recently, but he also had the engine rebuilt by his neighbor after doing the plugs. The LTFT is at 16-19 and never comes down. STFT is around 5-9 while driving. The engine vibrates a bit. I'm new to diagnosing and I don't have a scope yet. I trying to get more ideas of what I can check to figure out why it's running so lean. Thanks.
So LTF is adding a load of fuel and STF is also adding a bit of fuel at idle, vacuum seems alright.
Because it is a P0300 I am less concerned about individual cylinder problems than problems that effect all 4 cylinders.
A few questions ? Is the vacuum gauge fairly steady ? What happens to the STF at higher RPM & Load? Is the engine reving freely ?
The "engine rebuild" worrying it makes me wonder about the valve timing but the manifold vacuum is within the normal range. So first I think I would want to investigate if is a genuine lean condition or false lean, the O2 sensor could be telling lies. Also I would want to check the fuel pressure.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Last edit: 8 years 4 months ago by Andy.MacFadyen.
Vacuum is solid. Snap the throttle and it drops way down and recovers quickly. The fuel pump has been replaced, not sure when exactly. Doesn't mean it's not going bad already. If and when it comes back I'll take a closer look at the O2 readings. Thanks for the advice.
I would do an Injector test. also check fuel psi and volume.
if that is all good check mass air flow sensor for unmetered air flow.
last I would re check frt O2
Had the car in again today for an oil change and the p0300 is back, as I expected. I took it on a couple wot pulls and it would just go leaner and leaner. I learned that the shop has put 3 fuel pumps in the car in the past. I haven't been told to diag it yet so I only had a few minutes to mess with it. The O2 looks like it's doing its job.
Another symptom the car has is, if you turn the key to on engine off position and then try to start it 10 seconds later it'll either long crank and start or not start at all.
I'm leaning toward the timing being off. When I search p0300 in identifix almost all of them mention getting this code after the timing belt had been done. The car doesn't have maf and the fuel pressure regulator is on the fuel pump. It also doesn't look like it has an egr system.
BrainS wrote: Had the car in again today for an oil change and the p0300 is back, as I expected. I took it on a couple wot pulls and it would just go leaner and leaner. I learned that the shop has put 3 fuel pumps in the car in the past.
:lol: Nice. Did any of them bother to use a fuel pressure gauge? :silly:
I'm leaning toward the timing being off. When I search p0300 in identifix almost all of them mention getting this code after the timing belt had been done. The car doesn't have maf and the fuel pressure regulator is on the fuel pump. It also doesn't look like it has an egr system.
Definitely possible. I saw that you checked vacuum, and that it was solid, but what was the specific reading at idle? You can check the Cam Crank Difference and Cam/Crank Sync PIDs, but this will only confirm that that one of the cams is in time. Looking at MAP and Engine Load during another lean WOT run may show you a breathing problem.
I believe the vacuum was at 19". I highly doubt they ever checked the fuel pressure. I don't think there is a schrader valve, so it would take some extra effort to get a reading. The PID for cam and crank sync reads "good" while running, but it read "not good" during start up.
I highly doubt they ever checked the fuel pressure. I don't think there is a schrader valve, so it would take some extra effort to get a reading.
:lol: So true!
The PID for cam and crank sync reads "good" while running, but it read "not good" during start up.
Really? :blink: That's kinda interesting... Never seen one of these behave that way. This shot is from an '07 that wouldn't start due to no fuel pressure, and the Sync PIDs show In-Sync during cranking.
Wonder what those PIDs are doing during the long crank/no start. :huh:
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Looking at MAP and Engine Load during another lean WOT run may show you a breathing problem. 
