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I;ve been working on a “97 thunderbird. It’s been running rough, and smelling like it burns a little bit of oil. It never threw any codes at me till last week. It gave me P1151 HO2S detects lean. I have ruled out EGR problems, fuel pressure, Mass air flow, and didn’t find any leaks with the torch. I decided to do a compression test to see if it was worth throwing parts at to try to solve this very non-discript code.
The compression test came back with all 8 cylinders fairly close, but MUCH lower than what I anticipated. (59-69 psi.) I haven’t been able to come up with the compression ratio of this engine, but those numbers seem lower than what I would expect. Does anyone happen to know what those romeo 4.6L SOHC engines should test at?
Also, when pulling the plugs I noticed a little bit of carbon on all, but a few of them had ash deposits on them (and they’re not very old). This brings up the question of what is the likelyhood that a valve problem is causing the ash, low compression, and burning oil? How about a lean code? Could a valve problem cause the engine to throw a lean code? how about an intermittent miss?
I thought I would ask these questions before just slapping parts on. I recently watched my brother spend 3 grand on someone else to throw parts at a “bank 2 detects lean code.” And, the problem still isn’t resolved. Could valves be his problem too?
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now after some well needed sleep i have another idea. has it been going threw water? check to make sure it ant low. also how much oil does it go threw between oil changes?
It’s not really “going through” any water, but I do have a bit of a cooling problem. My temp gauge will go up to about 2/3rd’s of the way up before the cooling fan kicks on. Then it goes back to halfway. Thought it was the thermostat so I replaced that. Didn’t solve it though. I just chalked it up to the way it worked on this car, but maybe that’s related some how.
The oil: It seems to be between 1/4 and 1/2 of a quart low when it’s time for an oil change.
just took my daughter to daycare and the car threw two more codes. P1131 Lack of Upstream Heated Oxygen Sensor Switch – Sensor Indicates Lean – Bank No. 1. Last time it was bank No. 2. And, P0135 – Heated O2 Sensor Circuit. Brand new O2 sensors on the upstream. They are Bosch (I couldn’t find motorcraft anywhere).
Quoted From stormchicken:
just took my daughter to daycare and the car threw two more codes. P1131 Lack of Upstream Heated Oxygen Sensor Switch – Sensor Indicates Lean – Bank No. 1. Last time it was bank No. 2. And, P0135 – Heated O2 Sensor Circuit. Brand new O2 sensors on the upstream. They are Bosch (I couldn’t find motorcraft anywhere).
ok now that helps. but one issue. everything i can find shows that car has 2 up stream 02 sensors. so please make sure there is not a second upstream 02 sensor. next you need to check the wireing from each 02 sensor all the way to the computer connection looking for any bad or grounded spots. you should have a 4 wire 02 sensor. i am not so good at explaining wireing tests and i have not been able to find a good video that shows you. maybe Eric has one hidden some where? i will keep digging for a good video showing how to test the wires them selves and the 02 sensor.
don’t buy anything els just yet.
I would check for vacuum leaks again…your symptoms have vacuum leak written all over them. You want to diagnose the problem before you continue to throw parts at it. So what are all the codes that the car is currently throwing? Also, does the scantool you are using display PIDS?
I think starting with the check engine light codes is a great place to start however your description of the spark plugs and the fact that your engine smokes and runs rough may indicate that the engine has a mechanical issue. I know you didn’t do the compression test correctly based on your admition however if you remove the schrader valve form the tester you can do a quick leak down check to see if the engine is mechanically sound, if it’s not then no amount of sensors you throw at it will help, also I did not see where you checked for vacuum leaks however I will admit that I only skimmed though that part. Here’s a video on leak down testing showing what I’m talking about.
Compression testinghttp://www.youtube.com/watch?v=X_tbksFYhl4Leak down testinghttp://www.youtube.com/watch?v=W … ure=relmfu+1 for what Eric said rechecking the condition of the engine. if everything checks out good you can use a scan to with live data to do what is shown in the video here http://www.youtube.com/watch?v=djyyKlIVeMI let us know the results.
I’ve been looking for vacuum leaks again. I decided I was going to try to smoke them out. I got smoke out of one spot down by the fender well from a line I couldn’t identify but it was part of a line in the back of my throttle body. I repaired that, with no good results. The only other spot that I got smoke out of was the vents at the bottom of my EGR valve. Is it supposed to do that?
I actually replaced both upstream O2 sensors already. I did them at the same time.
I have been putting off the leak down test, I guess in the back of my mind, I just really didn’t want to know. Guess I can’t put it off anymore.
Quoted From stormchicken:
I’ve been looking for vacuum leaks again. I decided I was going to try to smoke them out. I got smoke out of one spot down by the fender well from a line I couldn’t identify but it was part of a line in the back of my throttle body. I repaired that, with no good results. The only other spot that I got smoke out of was the vents at the bottom of my EGR valve. Is it supposed to do that?
I actually replaced both upstream O2 sensors already. I did them at the same time.
I have been putting off the leak down test, I guess in the back of my mind, I just really didn’t want to know. Guess I can’t put it off anymore.
did you happen to pull the oil fill cap off while doing the smoke test? just to see if the smoke is getting into the crank case.
no i didn’t. but I will. I think I will try Eric’s poor man’s leak down test. I would even go buy a leak down tester, but I can’t seem to find one around here.
Quoted From moparfan:
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did you happen to pull the oil fill cap off while doing the smoke test? just to see if the smoke is getting into the crank case.I would do this, or pull the oil dipstick while it is running to see if there is any vacuum in the crank case.
Sounds to me like worn valve seals which would cause oil consumption and a lean condition. But I know very little about ohv engines.Okay, tried the smoke again. I couldn’t see it during the daylight, but under flourecent lighting I noticed a leak around the gasket between the throttle body and the air intake. I will replace that tomorrow and let you guys know what happens.
Thanks for all the help from EVERYONE. Please keep checking this thread in case this doesn’t solve the problem. And, I went and bought a compression tester so I could take the valve out of it and not feel bad about it. I will properly run a compression test and post the results.
Quoted From stormchicken:
Okay, tried the smoke again. I couldn’t see it during the daylight, but under flourecent lighting I noticed a leak around the gasket between the throttle body and the air intake. I will replace that tomorrow and let you guys know what happens.
Thanks for all the help from EVERYONE. Please keep checking this thread in case this doesn’t solve the problem. And, I went and bought a compression tester so I could take the valve out of it and not feel bad about it. I will properly run a compression test and post the results.
don’t worry i will stick around till the end. i really want to find out the issue to this one.
Here are the compression test numbers:
1: D 155 W 160 2: D 160 W 175 3: D 150 W 155 4: D 155 W 170 5: D 155 W 170 6: D 160 W 165 7: D 155 W 160 8: D 150 W 160
The only thing that seems off to me is that the first time I tested cylinder 2 it tested at 110 dry and 120 wet. After I finished with the rest of the cylinders, I rechecked it and it came back at 160 dry and 175 wet. Is there a condition that could cause variable compression on a cylinder like that? (other than user error)
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