14CUX running rich

Flyfish

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Oct 29, 2004
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RG tells me the tune is 3361

Not really. There are four manifold vacuum connections: to IAC solenoid (doesn't leak), to oil separator/PCV (doesn't leak), to fuel pressure regulator (doesn't leak), and to charcoal canister (haven't checked). Not sure if smoke machine would show anything with the charcoal canister, but... it might.
You could have a leak in the IAC itself or the vacuum advance diaphragm. Maybe you don’t, just an easy thing to check. Maybe try a different MAF and fuel temp sensor too if you haven’t already.
 

p m

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Apr 19, 2004
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I don't think I have a vacuum leak. Something else is making the ECU overfueling the engine - and it only started after I replaced the timing chain and sprockets.
Haven't scoped O2 sensors yet - but everything tells me the ECU would throw a fit if they were not switching between lean and rich, so they must be running. Bizarre. By now I know far more about 14CUX than I ever cared for.
Even what capability robertf wanted to see in Rovergauge and whatnot. My engine's a 3.9 and the tune is for 4.2, but it is within its capability to adjust. The same combo works perfectly fine in my other LWB and in an SWB.
 

Flyfish

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Oct 29, 2004
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I don't think I have a vacuum leak. Something else is making the ECU overfueling the engine
I don’t disagree since your vacuum reading was ok. Even a crack in the flex hose to the plenum may not be noticeable with a smoke test.

Maybe take a reading of the MAF voltage. If the running voltage is above 1.5v, you may want to try a different MAF. That could definitely cause a rich condition.
 
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discostew

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Sep 14, 2010
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Northern Illinois
Since you said this didn’t start till you did the timing chain it’s gotta be something in the front cover. I asked you about vacuum but you never told me what vacuum readings your getting. Did you put a gauge on it? Cam timing and ign timing are the only thing you could have changed. A vacuum reading would be helpful.
You said it ran better when you timed it my way but never said what the reading was.
If I had to do without a timing light or a vacuum gauge, the timing light would be in the damn trash.
It’s been a long time since I had to work on these regularly, but I think I started using a vacuum gauge because the balancer can start to fail and the outer hub can move on the inner hub and change the timing marks.
You only worked up front. So the problem will be...up front.
 

p m

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I thought I did... The ignition timing is about 12 deg BTDC, the manifold vacuum about 10psi.
It runs better now, but it still tends to get into this hunting idle mode - but more often than not, it settles.
Maybe more importantly, the short term fuel trims never go negative.

True about the timing cover, but - before I dove into it, the valve timing was way off because of badly worn cam sprocket, and both base idle and MAF bias voltage were tweaked before I bought the truck. MAF read 3.5V at idle.
Part of the issue is the 170F thermostat in this motor. It is too close to the 14CUX decision point on closed loop/open loop operation.
I totally enjoy the truck running super cool in the desert heat, but I may still bump it to 180F unit.
 

p m

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If you can’t get the thing to 18” of vacuum you have a problem. 10” of vacuum is pretty bad.
Stew,
Air pressure at sea level is 14.7 psi. 18" of vacuum is something that simply does not exist.
You must be thinking of 18" of mercury - I have about 19-20" inHg of vacuum.
 

Flyfish

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Oct 29, 2004
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Maybe read the air flow meter section on this link and see if it helps…

 

p m

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Apr 19, 2004
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Maybe read the air flow meter section on this link and see if it helps…

I think by now I know all of 14CUX piles of wisdom - this one, too. Well-written and a lot of good stuff.
Just too lazy to break out a scope and check the O2 sensors.
 

Blueboy

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Apr 20, 2004
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Back in the USA; Rockwood, PA
I think by now I know all of 14CUX piles of wisdom - this one, too. Well-written and a lot of good stuff.
Just too lazy to break out a scope and check the O2 sensors.
There are some great articles about the old 14CUX out there. Thx for this link.

Just buy new ones! You know you want them. 😁

Anxious to hear how this finally works out for you.
 

Flyfish

Well-known member
Oct 29, 2004
958
53
49
St. Louis
I think by now I know all of 14CUX piles of wisdom - this one, too. Well-written and a lot of good stuff.
Just too lazy to break out a scope and check the O2 sensors.
Wasn’t sure if if the detailed maf voltage info might point out something that’s way off. Just trying to pass along ideas that might help.