14CUX running rich

p m

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A little info:
1995 Classic with 3.9 built out of 4.0 block.

After my timing chain replacement, I put the engine together and ran it for about 3k miles now. It runs well, but it drinks gas like there's no tomorrow, and the idle sucks. It had a classic surging idle symptom - when the engine warmed up, it would go between 300 and 1000 rpm, and eventually stall.
The timing is at 8-10 deg BTDC, the TPS at closed throttle reads .32V (and goes up/down when it should), the MAF at idle reads 1.5V (and goes up and down when it should).
Both coolant and fuel temperature sensors work and read reasonable values.
Both O2 sensors work.
The IAC solenoid works and its operation can be observed.
There are no vacuum leaks in/around the intake - the idle stabilizes when I pull the PCV breather hose off- anywhere at the tee.
Fuel pressure regulator is tested and operational, pressure at the rail is steady at 35psi.

Yesterday I screwed around with base idle screw on the throttle body, and got it to run stable, but now the short-term fuel trims are pegged at 100% and the IAC solenoid position is also shown at 100%. The exhaust definitely smells rich.

Here's a screen shot of RS-RV8 app:
1619196146800.png

Any suggestions?
 

discostew

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with a coolant temp of 73 I would be looking at the coolant sensor and the fuel temp sensor connectors. One is grey and one is brown, but will connect to the other circuit. Both are right next to each other and very easy mistake to make.
 

p m

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with a coolant temp of 73 I would be looking at the coolant sensor and the fuel temp sensor connectors. One is grey and one is brown, but will connect to the other circuit. Both are right next to each other and very easy mistake to make.
Stew - the coolant temp is correct, it is a very cool-running engine. And I installed a new connector on the CT sensor not long ago, so no mixing the two.
 

discostew

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How about the fuel pressure regulator ? I just think if one of those injector grounds was pinched it would have more problems than this. I set these old distributors with a vacuum gauge, not a timing light. To me it's just more reliable. I turn the distributor till I get the best vacuum, then I drive it and back the timing off just a little bit at a time till it stops pinging.
 

p m

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How about the fuel pressure regulator ? I just think if one of those injector grounds was pinched it would have more problems than this. I set these old distributors with a vacuum gauge, not a timing light. To me it's just more reliable. I turn the distributor till I get the best vacuum, then I drive it and back the timing off just a little bit at a time till it stops pinging.
Checked operational.
I am with you on distributor timing - but I may have to do it with a timing light when time comes to smog it. Given that it doesn't ping on 87-octane gas, it could definitely take more advance.
 

discostew

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Checked operational.
I am with you on distributor timing - but I may have to do it with a timing light when time comes to smog it. Given that it doesn't ping on 87-octane gas, it could definitely take more advance.
It's going to run cleanest the way I do it.
 

discostew

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Robert, what's this thing? I wonder if I could make an adapter male -> wires with LED (with resistor in series and diode in reverse) -> female to use as a simple injector wiring tester.
Yes. I've made them with just a spade terminal that pushes into the female terminal of the harness.
 

discostew

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Really dumb question but is it possible you reversed the 02 senor wiring on the install.
You know what? this is actually a very good question. If that's what happened it will run fair or good untill it goes into closed loop. Then as soon as it goes into closed loop one side fuel trim will take off and go rich, the other bank will go lean. Till both are fixed at 26% or so and it will smell like shit and won't have enough power to get out of it's own way.
 

robertf

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Jan 22, 2006
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Robert, what's this thing? I wonder if I could make an adapter male -> wires with LED (with resistor in series and diode in reverse) -> female to use as a simple injector wiring tester.

Noid lights. They are too cheap to make
 

p m

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It's going to run cleanest the way I do it.
Stew, you underestimate California.
We [collectively as a state] are not interested in something running clean. The rules must be followed, even the most fucked up ones.
They check the timing at the testing stations.
 

p m

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Update:
- injectors: made my own noid light, tested 7 out of 8 (except for one right under the intake) - all check out.
- ignition timing: the engine runs better at ~12 deg BTDC, but that doesn't solve the problem.
- observation: the engine may start and run at normal operating temperature (72C) forever, until the ECU sees any throttle input. Once that happens, the short term fuel trims go to 100% within 10 seconds, and the idle starts fluctuating.
- IAC valve: the Rovergauge app shows its position as 100% (don't know what it is, but I guess it is fully closed/extended). I pulled the valve out - it was fully extended. Replaced it with a known-working IAC valve from another 95 Classic (plunger was mid-travel) - it went to fully extended as well. When I put it back to the truck it came from - it started with pretty low idle which eventually stabilized. It sort of indicates that I might have a vacuum leak somewhere - guess the only way to find out is to pull the top of the intake plenum.