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Amedee
Amedee, ASE Master Tech
Category: Car
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Experience:  ASE Master Tech advanced level specialist. Wisconsin certified emissions state inspector
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We have a 2000 Daewoo Leganza that started losing engine power gradually about 6 months ag

Customer Question

We have a 2000 Daewoo Leganza that started losing engine power gradually about 6 months ago. Engine power loss is now severe, and can be observed in gear and in neutral. Will not rev to above 500o rpm and falls back to ~3000 almost immediately. Compression, ignition spark, fuel pressure all good. Replaced both camshaft and crankshaft sensors without improvement. What can be wrong?
Submitted: 2 years ago.
Category: Car
Expert:  K. Wiggins replied 2 years ago.
Is the check engine light on, and if so have you retrieved codes? Also have you checked fuel pressure?
Customer: replied 2 years ago.
Check engine light has come on, codes 342 and 341 were retrieved, but do not always show up right away sometimes takes 50-80 miles for codes to return, even though engine performance still sucked for the entire time. Checked fuel pressure - 45 psig with fuel pressure regulator disabled and 38 psig with regulator enabled.
Expert:  K. Wiggins replied 2 years ago.
The 341 code is a result of the 345. Even though you have new sensors there is still an issue.

MY first line of testing would be the battery and starter. If the cam sensors do not receive proper voltage during cranking these codes will set causing the problems.

Load test battery nd confirm good
PErform a voltage drop test while starting engine. (reason being if the starter is drawing too much the ecm will not get required voltage to send to sensors. Heres a link to how to test

http://www.freeasestudyguides.com/voltage-drop-test.html

^copy and paste in web browser

If all the above checks out you need to test the wiring to those sensors for open or short.
Customer: replied 2 years ago.
This car does not list a 'code 345'. Did you mean 'Code 342'? I have monitored engine (battery) voltage during operation and it is always steady (no erratic fluctuations) and between 12.9 volts and 14.4 volts while the engine is operating.
These codes are not being set when the engine is started, but only after at least 30 minutes of operation.
How will this affect engine performance even when the diagnostic codes are not set or active? The manual says that if no valid camshaft position data is being acquired by the ECM ('Engine Control Module') the ECM uses a fall back method for timing of fuel injection sequence and spark timing called 'Alternating Synchronous Double Fire' method [ASDF}, which has a 1 in 6 chance of being the correct injection sequence. However, the ECM should not be using the ASDF timing unless it has set either Code 341 or Code 342.
In the morning, I will perform the voltage drop test on the starter cable as indicated in your link, though I do not understand how high resistance in the starter cable can affect engine operation after the starter solenoid is disengaged. The alternator output has already been checked as well, and found satisfactory.


Expert:  K. Wiggins replied 2 years ago.
MY apologies on 345 I misread it. I would recommend the starter test though as even code 341 lists that as a possible issue. The problem with a high draw on the starter circuit is that it does not allow enough voltage to the computer. The computer used a 5 volt reference signal to compare return readings from sensors to. If that reference voltage is not 5 volts it will cause erroneous readings.

THe reason you do not see the engine light come on immediately is because the error has to be seen for a certain amount of time. During that period it is stored as a pending code and will not show up on some scan tools.
Customer: replied 2 years ago.
My scan tool does show pending codes, and there are none present until after the car has been driven for at least 30 minutes, and sometimes not even then.
The poor engine performance is immediate and constant however. [Unfortunately!]
Expert:  K. Wiggins replied 2 years ago.
I would suggest to test for continuity between each wire at the sensor and the ECM. Also check the ground at the senor connector. I do not have diagrams for the ecm and senor pinouts so I will open this up in hopes another expert might.
Customer: replied 2 years ago.
I have the wiring diagrams and will check the wire continuity and grounds. I will let you know hte results in about 10 -14 hours.
Thanks.
Expert:  K. Wiggins replied 2 years ago.
Sounds good I'll be around
Customer: replied 2 years ago.
My daughter was moving into her new apartment today - so I had to put aside my tools to carry boxes and furniture. Thus I was not able to complete the wire testing.
Tomorrow, hopefully.
Expert:  K. Wiggins replied 2 years ago.
Sounds good, I'll be in and out all day.
Customer: replied 2 years ago.
Sorry this took so long. Life got in the way!
I checked wiring from camshaft sensor to ECM, BAT+12V, and engine ground. They were all good. Battery was weak, so I put in a new battery. I went for a test drive and the results were unchanged. The engine still develops very low power. I rechecked the fuel pressure at higher rpm levels, and it stayed at specification ~37psig at engine rpm between 850 and 5000. (I was hypothesizing that the fuel filter was partially clogged and developed serious pressure loss at higher flow. Hypothesis was disproved.)

Do you have any alternated theories?
Expert:  K. Wiggins replied 2 years ago.
Hi Rob, I'm going to research this a little deeper. I will be out for some time tomorrow with family obligations so i will open this up to other experts in the mean time.
Expert:  AMD replied 2 years ago.
Hello,

Different expert here, I will try my best to help here.

Did you check the timing of the engine? I'm thinking your engine is out of timing, Can you pull the front cover off and check the timing belt marks? I have instructions if needed.
Customer: replied 2 years ago.
Yes, when I replaced camshaft position sensor. Timing belt and camshafts were correctly aligned.
Expert:  AMD replied 2 years ago.
OK did you check the area where the camshaft sensor reads off?
Customer: replied 2 years ago.
There was no visible damage or wear on the camshaft gears or the mounting surface . The camshaft position sensor mounts to the head with two bolts which seem to 'fix' its' position and orientation. The magnetic proximity sensor that is the camshaft position sensor is essentially going to send a 'pulse' or count for each tooth of the timing gear that passes through its sensing zone. As I said, there is no visually apparent damage or wear, the sensor itself is brand new, and the wiring has been checked.
Also since the engine runs for sometimes hours without a 341 or 342 code, it seems fair to assume that the camshaft and crankshaft position sensors are functional as of now. The crankshaft sensor that was replaced had damage to the conductor and outer insulation sheaths near the top of valve cover. This damage was hidden under careful wrappings of black electrical tape. Since I did not tape this up, it could have only happened four or five years back when we had a shop replace the oil pump water pump and timing belt, or even earlier when some body damage was repaired or when some factory recall work was performed by a dealer. Regardless, the car ran well for years with the electrical tape repair, and now the entire sensor/cable assembly has been replaced with a new part.
Expert:  AMD replied 2 years ago.
I am running out of ideas here, I will opt out and open the question to other experts to share their input.
Expert:  Amedee replied 2 years ago.
Hello!

New Expert here!

Can you tell me the engine vacuum at idle and at 2500 rpm?
Customer: replied 2 years ago.
I finally gave up and took the car to a shop so I cannot check that right now. However from my recollection, checking the vacuum is one of the first tests in the Daewoo manual for 'loss of power', and it was in specification as far as I recall. Though that was probably almost two months back in this saga. Strictly from memory, I think MAP readings from the scan tool were in the 6 - 8 psia range, and went up as high as 14 psia at full throttle. What are you thinking might be associated with good or bad values for engine vacuum?
Expert:  Amedee replied 2 years ago.
Incorrect valve timing, plugged exhaust, restricted intake system and so on.. A lot of things will affect engine vacuum.
Expert:  Amedee replied 2 years ago.
If you can get me the map readings it will help out big time.

Also, if you would like a test to help with this diagnoses.. you could give it to your mechanic to help him diagnose this condition. Just let me know!
Customer: replied 2 years ago.

I'm very sorry for the long delay in this response.

This was our third visit to this mechanic. On the first visit, they saw that the signal from the crankshaft position sensor was poor and erratic, so I replaced this sensor. I noticed when I removed the old sensor that a 3" section of the sensor cable (where it passed over the valve cover) was carefully wrapped in black electrical tape. The only times anyone else had done any work on this engine were about eight years ago when a dealer took care of one or two recall issues, and about four or five years ago when the oil pump, water pump, and timing belt were replaced. After replacing this sensor, the problem remained, and the ECM again showed camshaft position sensor problem codes. We took the car back to the mechanic, and they stated that both sensors' signals 'looked' clean on their oscilloscope. They suggested replacing the camshaft position sensor as an experimental repair and charged me nothing for this visit though I know they spent at least two hours looking into this. I replaced the camshaft position sensor. Afterwards the problem was still present. This lead to the third trip to the shop. After reviewing the history, and taking a test drive they looked for a restriction in the exhaust. This car has two catalytic converters, one immediately downstream of the exhaust manifold, and one under the car upstream of the muffler. As the downstream converter's bolts were easier to release, they looked at this one first. They found that though there was no apparent external damage, the ceramic catalyst support been breaking apart and collecting in the outlet port of this converter,gradually restricting the exhaust more and more so you were also on the right track.

Thanks!

Expert:  Amedee replied 2 years ago.
EXCELLENT! I am glad I could help! Its been a pleasure working with you.

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Amedee
Amedee, ASE Master Tech
Category: Car
Satisfied Customers: 21939
Experience: ASE Master Tech advanced level specialist. Wisconsin certified emissions state inspector
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