Click/Clank only on Cold Start

Hey all,

Hoping to get any more insight into this noise I am hearing. Only on cold start, where the truck has been off long enough for the SAIS to start, I will hear a single click/clank noise like a second after I start the truck. I've been trying to think about what could make that noise only once but I'm left wondering as it doesn't happen once the engine is ran. Engine runs great with no other noises once it is running.

It sounds exactly like when the AC clutch engages, that same mechanical click sound. The truck is started with the AC off so the AC clutch isn't engaging. I haven't been able to have someone else start the truck to let me listen but if I get the opportunity I will post an update if I can narrow in on the location.

Thanks all in advance for any help, I greatly appreciate it.

 

I feel like we may be missing some details.

Does the truck start correctly, rapidly as usual, it just clicks at the initial turnover?

Is it a single click, a repetitive click, does it follow a pattern?

 

Hey Shifty,

The legend himself. First I want to thank you because your posts on this forum have helped me with a plethora of projects I have done on the truck . Appreciate all the help you give on here.

To answer your question, the truck turns over just fine, rapid as usual. After the truck has turned over and started, I will here that single click usually a second-ish after it is running. Only during the cold starts though, once it has ran and I start it again, no noise which is what makes this so tricky. As mentioned the noise is sounds like an AC clutch engaging, that same sound of mechanical engagement is the best way I can describe it. I start the truck with the AC off so the compressor is not on for startup.

I'll provide any other information needed/requested as quick as I can, currently at work so I can check back in here every so often.

Thanks!

 

No legend, just ADHD fueled insanity.

So, it's super curious to me. There's not a ton I can think of, but because you have the VVTi version of the V8, as all 2005+ with V8 do, your truck has the Secondary Air Injection System "SAIS" or some say "SAI". It seems you know this, but I'll add some input that may get you thinking about this, and about what to look/listen for.

That system itself consists of a couple of things:

• A pump under the intake manifold, bolted to the top valley of the engine; this pump supposedly had a foam seal inside that tended to degrade over time, and could jam up the pump (or its valves located elsewhere, more on that in a sec)
• A pair of orange-ish-brown solenoids with lots of short vacuum cables sitting above the passenger valve cover/fuel rail
• A pair of valves on the back of the intake/heads - you'll a fatter vacuum hoses routing from those solenoids to the rear of the intake to control thos valves

If my memory serves, and sometimes it doesn't so don't quote me on this...

It's clever to note it only happens on cold starts. SAIS is programmed to operate, at the most basic level, when two conditions are met, and I'm dumbing it down significantly:

• Start running for first 30-60 seconds if this is a cold start
• UNLESS the temperature is below X° outside (this is how basic bypasses work: Trick the ECU into thinking outside temp is too low to run SAIS)

When the SAIS engages, it's supposed to open the valves at the back of the head to allow hot exhaust to recirculate and heat things up faster. I assume (not sure) the pump starts pumping, and either vacuum triggers those two solenoids to open air from the pump to kick open the valves, or there's something electrical happening with the valves that cause them to open. I'd need to look at the vacuum routing to see if I could make heads or tails of that part of it (or RTFM, maybe they say in the FSM).

Anyway, those valves, I've seen pictures, and I believe it's just a simple butterfly internally. I wonder if the sound you're hearing is either (A) one of those valves slapping open, or (B) one of the solenoids kicking open?

I'd listen to hear if you hear a similar click sound when the pump spins down, if you can't get there in time to hear when the pump spins up.

Or, if you can get someone else to start it cold, listen to hear if the sound is coming from above the engine, or behind it, or somewhere else.

 

I did find this cool diagram of the SAI system circuit in the FSM:

​

 

Thank you for the detailed response, I was also leaning towards it was something with the secondary air system engaging. The system is getting old, it does have the vacuum noise when it is on that people state that is when it is starting to go out. It has made that vacuum noise since I bought it but I'm unsure about the click noise. This is one of those moments to where in my memory, I don't remember ever hearing this noise until one random day, then the noise sticks and you notice it every time. The problem I ran into is I could find no other relevant thread anywhere regarding this . I'm going to see if a coworker can help me here in a bit while I sit in the engine bay and see if I can narrow down the location.

Thanks Shifty for all the help/info so far!