Is it necessary to position the camshaft correctly to seal valve openings when performing a smoke test for vacuum leaks? Or would either the intake or exhaust valve be completely closed in each combustion chamber for any given position in the rotation of an engine? I could not find anything on this with a search. That gets me thinking that perhaps it is not necessary to fret about the camshaft position.
Jack
Why the smoke test?
Fuel trim fault codes?
P0171 on a 2011 Accord 2.4L. I think it may have been the MAF. I could not find any vacuum leaks with a visual inspection, or with a hose to my ear. I cleaned the MAF, but no luck. Swapped it out and cleared the code and so far so good for a day. I just thought I would try a cheap diy smoke test if the code came back. I got to wondering if the valves in any given cylinder would both be open at the same time and was too lazy to think about it at the moment. But if I had to put even money on a bet I would put it on them never being both open even a little at the same time.
don’t worry about the valves
are you using a proper evap/smoke machine, btw?
I’m not using anything at the moment. Don’t have anything. Was just curious.
Has your shop measured the warm idle intake manifold vacuum? After a quick visual inspection, that’s where I’d start with this problem. I’m just a knucklehead diye’r with no Accord experience, but I’d guess the normal intake manifold vacuum would be around -20 in hg at warm idle. For comparision, -21 on my Corolla, -18 on my truck.
Do you understand the concept of fuel trims, George?
No idea. Just a knucklehead diyer. Niether of my cars has fuel-trim display capability, so no experience. I’d be happy to learn from your explanation how it is done though. I expect others would too. Care to teach us?
You use a $50 code reader to show fuel trims. Short/ long. Not complicated. If I had maf issues I’d inspect the intake hoses. Inspect like remove them and flex them as they are usually molded bellows type hoses.
Thanks, George, there are other issues with this engine, and what with working with the owners, their neighbor and trying to keep track of the symptoms, I plumb forget to do a vacuum test, even though when, in the relative quiet of the evening, I often thought that I should check the vacuum. I was installing a new garage door on my garage at the same time and have just recently recorded what has been done to address the various symptoms, the worst of which was a no-start when hot condition. In addition to the P0171 that kept coming and going, the ECU started throwing a P0507. This latter was also a long-time issue that the owner kept clearing with a code reader. It came back since I got involved. The actual condition on this car that is associated with this code is a fluctuating idle. I’m pretty sure I got it in hand.
Funny thing, the owner took it to a shop to try to deal with the no-start when hot condition and they shop read the P0171 code and decided on the spot to change the O2 sensor. When I heard about it I thought it was like shooting messenger.
These people are friends and have been living with these issues for about a year now, so there is no hurry. I am certain I can get the car right again. They trust me 100%. It is a matter of another week when a new throttle body arrives to deal with the fluctuating high idle. You can’t buy a new throttle position sensor or a new idle air control valve for this car. You have to buy a whole new throttle body. And you have to be careful which one you buy, as some are sold without the IAC valve. If the IAC is the problem, you are stuck if you buy a TB without it.
Did all that, and checked all the vacuum hoses. Nothing visual. I also scanned everything with a hose to my ear. Nothing. Cleaning the MAF sensor with the CRC MAF cleaner did not help, so rolled the dice and put in a new one 2 days ago. So far, no return of the P0171.
Have someone test the residual fuel pressure.
When the pump is turned off or stops running, the system should hold residual pressure for several minutes (look up the specs to see how much pressure drop is allowed over a given period of time). If pressure drops quickly, the vehicle may have a leaky fuel line, a leaky fuel pump check valve, a leaky fuel pressure regulator or one or more leaky fuel injectors. Low residual fuel pressure can cause hard starting and vapor lock during hot weather.
Tester
Thank you, tester. I was looking for a Schrader valve on the fuel rail but found none. After investigating online with the owner we found the way to do it. That was yesterday at their place, but it was late and I did not have a pressure gauge with me.
That may indicate a problem with the electronic throttle body.
I would try cleaning it to see if it helps.
Tester
I inspected it. It was very clean. It did not look at all gummed up like I have seen. We have a new one coming soon, as the TPS and IAC valve are integral with the TB and can’t be purchased separately.
That’s the same as my Corolla, as pertains to the idle air control valve. I know how frustrating that is. The TPS on my car is however independent of the throttle body.
On the bright side, China is cranking these TBs out for cheap. The seller on eBay has close to 50 thousand sales of auto parts with a 99.1 positive rating, and everyone who bought this particular throttle body gave it a positive review. It only cost the owner $57. The car has over 210,000 miles on it. Seems like the way to go. I saw this part sold on RockAuto and the chain stores for $375 and more and they didn’t have the IAC valve. We will see if it deals with the P0507.