Re: 99 X EB 2WD V8 Rough Idle

Jul 01, 2003 1 Replies

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Sonny 23 years ago

Thanks Jim, is the intake gasket a known problem with the V8 also? I have done a lot of part changing as you can tell by my 1st post, is it possible a injector could be malfunctioning causing the idle issue? There now are no codes when I got them pulled at AuotZone. Also, the gap at .052 is this the correct gap for the V8 my Owners manual said .052-.056, would adjustment here be worth trying and if so which way to go?

BTW the only parts I did not replace myself were the DPFE and the EGR, these were done by the dealer (Not Ford) I bought it used from. They 1st replaced the EGR so they said, because of a CEL and code Insufficient EGR flow, CEL came back on and then they replaced the DPFE. I do know for a fact this was replaced as the original was a cast metal and the replacement is black plastic. I am wondering if the EGR was never replaced that it could be giving me some problems even without a CEL or codes, your thoughts on this.

Thanks again...

Sonny.... since the problem appears to happen at low rpm or idle, I'm
> inclined to think vacuum leak first. At idle, any "unauthorized" air will
> make up a larger portion of the intake charge than at higher rpm. Both
> flavours of 4.0 are prone to intake leaks and many can be nearly impossible
> to find without a teardown. The only thing that worries me about this
> diagnostic is that the intake gasket problem for the OHC usually disappears
> with the rise in operating temperature..... I say "usually" since I'm a long
> way from having seen 'everything' and seem to see something I never saw
> happen before nearly every day 8^(
>
> I've even heard of techs not finding anything with smoke machines find a
> problem when they finally decide on a teardown.
>
> I haven't heard of it with the OHC yet, but there remains the chance that
> internally blocked EGR passages may direct most or all of the EGR flow to
> one cylinder...... through the mid years ('99ish give or take) there were
> (IIRC) three different intake manifolds tried.... I don't have my manuals
> handy, but if yours has IMRC there may be a problem with the mechanism of
> valve blades, as well.
>
>
> --
> Jim Warman
> snipped-for-privacy@telusplanet.net
>
> > I have a rough idle, more like a steady pulsating vibration with a slight
> > miss hot/cold // AC on/off. 47k on the truck, I have changed the TPS, IAC,
> > EGR and the DPFE. Cleaned the MAF new Motorcraft Plugs .052 gap, new
> > Motorcraft Wires, fuel pump (for pressure loss) and the fuel filter. New
> > battery also. I have tried running injector cleaner 2 times, good gas > also.
> > I have used carb cleaner to check for Vacuum leaks, NOTHING... The truck
> > seems to run great down the road, good pickup, smooth feel. But at Idle it
> > has the roughness. NOTE: sometimes it seems to smooth out and the > roughness
> > is less, this only seems to last for a short period of time (miles) then
> > back to the same thing. I really think I should have a Smooth idle but > just
> > cannot seem to get it right. I do most all my own work. Oh, 1 last thing > the
> > idle seems to vary, when the truck is warm most of the time the Idle is
> > about 600-700 then sometimes it is 700-800 There is no difference with the
> > idle smoothness when this happens.
> > Any help?? JIM W.???
> > Thanks
> >
> >
>
>

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Jim Warman 23 years ago

OK.... I didn't notice an motor size and just kinda 'assumed' 4.0..... me bad - normally I whack people on the pee-pee for forgetting stuff like that

8^)

In another thread, I got the impression that AZ can only access On Demand DTCs...... continuous codes and KOER codes are important in the diagnostic process too..... more-so when we don't have ODDTCs to work with. Unfortunately, this may mean a trip to a shop that charges to scan codes.... just to get any CMDTCs or KOER DTCs.

Truth be known, if you are within .010" of the recommended plug gap, you wont notice any difference unless there is another inherent weakness in the ignition system (gives you a range of .042 to .066 with no appreciable problems)..... no, I'm not suggesting we forgo gapping plugs properly, I am saying that a properly functioning ignition system can be quite forgiving.

There remains the possibility of an intake leak from the bottom of the intake manifold - not unheard of but fairly rare. The DPFE is a real problem...... good way to measure EGR flow but it has a lot of problems with lifespan. Generally, DPFE or EGR valve problems will affect all cylinders somewhat equally. A "drooling" injector might give your symptoms but you'd need a fuel pressure guage and about three fuel pressure tests just to see if the problem is in the fuel rail or not, let alone isolate it to one cylinder.

A shop with an adequate scanner can access misfire data which may reveal the offending cylinder. A good enough scanner will allow a cylinder balance test that may offer more information. At 47K miles, I'm shy to consider a compression problem but then "nothing is written in stone". A low rpm cylinder contribution test 'should' give a hint about a cylinder not contributiong what it could/should.

Most ignition problems manifest themselves when cylinder pressures are high..... acceleration, high rpm operation...... qualifying statement time - if mixtures are lean at idle (back to the vac leak scenario again) it can be difficult for the plug gap to ionize... the first step in the spark jumping the gap.

The only thing I can recoommend at this point is to find someone with a scanner with good capabilities..... particularly CMDTCs AND KOER capabilities.... we have a 50/50 chance of coming up empty or finding something we can use.... Be sure to get the exact code numbers rather than code explanations....

-- Jim Warman snipped-for-privacy@telusplanet.net

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