Hello YotaTech members,

After some help I received on a different thread, I found out that my PAIR valve was not working correctly.

After some investigation, I found that the signal wire (presumably from the ECM), was giving the VSV the command to stay open sometimes. The two scenarios for it to stay open are when the engine is idling below -15 degrees TDC and when the the engine is settling after revving up (which is supposed to be normal per the FSM). This video shows what's happening:

http://youtu.be/5QtLClk2c7w

Any idea on why the pair is receiving the command to stay open? All hoses/tubes are in the correct place.

 

So why did you start a new thread?

 

at factory timing, is this an issue?

 

Hey Bob C., thanks for your help on my other thread. To answer your question:

This thread is new so that it has a relevant title and topic to the thread. It helps other users find tag-searchable results (via google, etc.), so that anyone else who may have a PAIR problem in the future will not have to wade through 14 pages of a post with the topic "My engine sounds funny".

 

At factory timing, -10 TDC, the PAIR will open when dropping RPMs. This is normal per the FSM. The loudness of the noise is not normal, and gets evil glares from pedestrians when I'm driving. It sounds like the Jake brake on a big rig.

 

I still don't see where the PAIR valve lines are plumbed to since you put in a retarded cold air filter kit (don't get me started on those~). The stock unit has an expansion chamber that the PAIR hoses connect to....???

 

 

I bought the truck two months ago... All mods on it were not me. I've even been to the junk yard to look for the stock air filter. Are you saying that this noise would otherwise not be there if the resonator and stock air filter weren't there? This noise didn't exist before I replaced the head.

 

I don't know.....sounds like something was changed during the head job. Do you have pics of the PAIR valve hose ends & where they connect?

 

1. PAIR operation has nothing to do with the ignition timing in a direct sense. The ECM doesn't use the ignition timing angle to determine when it should/shouldn't be operating.
2. The ECM uses coolant temperature, engine speed/rpm, VAFM signal, and throttle position to determine when to switch on the VSV actuating the PAIR.
3. Yes, the noise created by the pulsations will be louder if there's no resonator and/or air filter box present.
4. I'm not sure that it's PAIR related at all. SINCE ignition timing has nothing to do with why/when the ECM signals the VSV for the PAIR.
5. HOWEVER, because you are advancing the ignition timing the engine idle speed/rpm is going to increase too. More advance = higher idle rpm. And engine speed/rpm IS a determining factor.
6. Maybe there is something wrong with the PAIR system. I don't know for sure. I do know I never heard such sounds while advancing the ignition timing on mine when it used to have a PAIR. Hint hint...
7. Where does the sound appear to be coming from exactly? When I watch the vid it sounds like it's coming from the distributor or there abouts.

 

Dead on, MudHippie. The PAIR wasn't really the problem, as you pointed out, and the timing doesn't directly relate to PAIR operation. What I found was a vacuum leak at the compression fitting for the EGR valve, and two spark plugs with micro-cracks in them (probably from taking them on and off). It seems that #1 an #3 cylinders would misfire from occasional lack of ignition. I'm still not sure why that would cause the PAIR to roar so loud, but as soon as I replaced all the spark plugs, the PAIR quieted down a lot.

Aside from a small drip out of a water hose, the engine is running great. Now to find a stock air box with resonator at a junk yard. Thanks for all your help, YotaTech community!