RPM flare at start up

[john cris]

Hello,
Been trying to figure out why my 2003 explorer 4.0 SOHC starts with a quick rpm flare. It only lasts a moment but has been this way for at least a year. The motor runs good , idles smooth, and gets decent fuel mileage. It does not exhibit any time chain noise. It does have the all to common start up squeal / squeak . I've replaced the belt, tensioner, idler pulley and alternator trying to chase that down. No fix so far. I've begun to wonder if these issues are related? I've been all through several forums checking the possible causes. I'm a decent mechanic as I've been wrenching all my life (60 years old). I've tried motorcraft parts and nothing has helped. Can anyone weigh with a suggestion?
Thank you,
Jcris

 

[silverfox103]

I have a 2003 Aviator V8. It does the same thing, but it runs great. I've read of other forum members with the same condition. I haven't seen a solution, but it doesn't really seem to be hurting anything.

Tom

 

[apenland01]

RPM flare is normal, squealing is not. I don't have the 4.0L, but I would say just make sure all the pulleys are clean and no oil/coolant/steering fluid is leaking onto the pulleys making it slip. Otherwise, you could look at the sticky about the harmonic balancer for the 4.0L.

 

[apenland01]

I have a 2003 Aviator V8. It does the same thing, but it runs great. I've read of other forum members with the same condition. I haven't seen a solution, but it doesn't really seem to be hurting anything.

Tom

RPM flare is a normal event for these Explorers. I've heard 2 theories on why this is the case. First, the intake manifold is not under vacuum yet, so it flares. the other is that the timing chain tensioners are pressured by oil pressure, so there is a short flare to make sure the oil pressure rises quickly.

In my case, the engine hits about 1400-1800 for 2 seconds and settles down to an idle of 500-600 after about 20 seconds or so. It's been doing that since I bought it new.

 

[john cris]

That is very interesting and odd at the same time. I don't recall the motor starting this way a couple years ago. It does seem something has changed but what you say makes sense . It is odd though as I don't recall any vehicle I've owned staring with this "flare". How could it be ford engineers would create such a noticeable issue and NOT work to find a better resolution . I do appreciate your viewpoint as its one I've not heard before. I will probably continue to try and determine the cause and resolve it. I think I'll find a 3rd gen explorer and test this information .
In the mean time I'll try and figure out what's going on with that start up squeal
Regards,
John