# p0303 and p0171. mechanic smells coolant in exhaust.



## skylark (Nov 3, 2020)

to start I had a p0303 error when driving and had my mechanic check my plugs even though they were replaced 6 months ago. Found the wrong ones were installed and cheap. Also the leak I had in the valve cover was still happening. replaced the plugs with good ones and a valve cover kit. 

A few days latter got a error p0302. replaced the coils. Things were driving good but started to have a issue with the rpms fluctuating and got a p0507. Took to fire stone because my mechanic was unavailable. Found I needed to replace a sensor in the throttle body. After the repair the engine seemed to start a bit week and after a day same issue with a p0171on my scanner. They were not able to verify the code and actually said the car sounded really good. 

A few days latter got a check engine light on the way to the mechanic again. When I was getting it into the mechanic and found I had to come back the next day The car actually didn't start when I tried to leave.. They diag and verified the codes p0303 and p0171 also said they smelled coolant in the exhaust. Said the car started right away for them.

any ideas?


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## rogoman (Dec 16, 2004)

skylark said:


> to start I had a p0303 error when driving and had my mechanic check my plugs even though they were replaced 6 months ago. Found the wrong ones were installed and cheap. Also the leak I had in the valve cover was still happening. replaced the plugs with good ones and a valve cover kit.
> 
> A few days latter got a error p0302. replaced the coils. Things were driving good but started to have a issue with the rpms fluctuating and got a p0507. Took to fire stone because my mechanic was unavailable. Found I needed to replace a sensor in the throttle body. After the repair the engine seemed to start a bit week and after a day same issue with a p0171on my scanner. They were not able to verify the code and actually said the car sounded really good.
> 
> ...


If you're smelling coolant in the exhaust, then there may be a blown head gasket. Perform a compression test to verify. The normal procedure for a compression test is to remove all the spark plugs, insert a compression gauge into the spark plug hole, and then turning the engine over about three times. Record the reading; do this for all the cylinders. If there is more than a 20% difference in any of the readings, a further test would be required to determine if the variance problem is due to an issue with the piston rings, the valves or the head gasket. *Post* the readings here on the forum.
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P0303 is set by misfires and P0171 is set by several possibilities such as vacuum leaks, incorrect fuel pressure, etc.

Several things that could cause misfires:

The camshaft position sensor may be marginal.
Incorrect fuel pressure. Tee-in a temporary fuel pressure gauge between the fuel feed hose and the fuel rail. The readings at idle should be 51 psi.
There may be a major intake system vacuum leak. To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be 21 InHg. If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.
Dirty fuel injector(s). Run some good injection cleaner, like BG products 44K, through the system; give the cleaner about a week or two to do it's job.


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## skylark (Nov 3, 2020)

rogoman said:


> If you're smelling coolant in the exhaust, then there may be a blown head gasket. Perform a compression test to verify. The normal procedure for a compression test is to remove all the spark plugs, insert a compression gauge into the spark plug hole, and then turning the engine over about three times. Record the reading; do this for all the cylinders. If there is more than a 20% difference in any of the readings, a further test would be required to determine if the variance problem is due to an issue with the piston rings, the valves or the head gasket. *Post* the readings here on the forum.
> ----------------------------------------------------------
> P0303 is set by misfires and P0171 is set by several possibilities such as vacuum leaks, incorrect fuel pressure, etc.
> 
> ...


Thanks its very frustrating. The car runs very good and even the mechanic was commenting on how good the car ran before this started. I understand this issue with fixing one thing and something down the chain that was weak would fail but this head gasket issue is strange. The engine was starting and driving fine before I got the first misfire. And Its not like I was driving for months with no repairs. I am usually on top of reairs and do scans for soft codes that wouldnt give a check engine light. The smell just starting while at the mechanic. Only issue I had was the lean fuel issue. My mechanic is available again. I will take to him. keep you updated. fyi don't ever use firestone.


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## smj999smj (Jan 1, 2006)

Do you smell coolant in the exhaust? It's a bittersweet smell.


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