41-lean
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Mountain Pass
Joined: Oct 2016
Posts: 172
Likes: 1
From: georgia
i built an egr block off plate to stop that vaccum leak. i was reading and heard it was bad to pull the plug wires off of the motor when it was running? i also replaced the pcv grommet and valve. because smoke was leaking out of that as well during the smoke test. and the missfire is still there. i also reset codes41, 31, and 75 still come up
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Mountain Pass
Joined: Oct 2016
Posts: 172
Likes: 1
From: georgia
yesteday after installing the egr block off plate and pcv valve and grommet i also poured in a can of bg 44k and on the way to work today i didnt notice a misfire not once. ill know in a couple days tonight ill also pull plugs and see if i can find that misfiring cylinder
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Mountain Pass
Joined: Oct 2016
Posts: 172
Likes: 1
From: georgia
TOday at lunch I tried pulling spark plug to find the misfire. They all affected the engine. So I smoked it again there's no vaccum leaks. So I moved to fuel pressure. At idle with the regulator hooked up pressure is 31 unplugged it's at 41. Could that be the problem? It has a rebuilt fuel pump and new filter
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Mountain Pass
Joined: Oct 2016
Posts: 172
Likes: 1
From: georgia
i drove home with the regulator unplugged and vacuum line capped. surprisingly it felt like it drove better didn't seem to misfire even when i tried to force it. i have a decent drive tomorrow ill try it again. ill have to buy a fuel pressure gauge now seeing that today was the last day at my job.
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Mountain Pass
Joined: Oct 2016
Posts: 172
Likes: 1
From: georgia
just read codes again, still the same. when the computer is running its test and raises the rpm. its very smooth and then you can kinda hear the miss especially in the exhaust
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Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
31 – (EVAP control system below minimum voltage) Check & clean the connector to the purge valve.
75 -Identify & mark any wires or connectors on your 1990 wiring harness that are not connected.
75 -Identify & mark any wires or connectors on your 1990 wiring harness that are not connected.
Cargo Master
Joined: Mar 2010
Posts: 3,342
Likes: 294
From: Laramie, WY
I would start with checking fuel pressure under load. I route the fuel pressure gauge between the hood and cowl, then set it on the windshield so I can read it while driving. See what the pressure does when accelerating. The other info that would be helpful is the oxygen sensor voltages but I don't know how to get those with EEC-IV systems.
Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
The lean indication could be because you are actually running lean & fuel pressure does need to be verified.
A lean indication can be due to a low or lack of O2 signal to the computer from one of the sensors.
If the heater is not working in the O2, a low or lack of O2 signal to the computer can occur.
Power to the O2 heaters can be measured.
A signal from the O2 sensors can be measured.
The common ground wire for the Heater & the O2 Signal in each Sensor are very important and can be verified.
Typically, when the computer receives a lean indication it compensates by adding additional fuel delivery to the engine.
If the O2 sensors are not working properly, and the computer is compensating by adding additional fuel delivery the engine will run rich all the time.
Are the O2 sensors New?
A lean indication can be due to a low or lack of O2 signal to the computer from one of the sensors.
If the heater is not working in the O2, a low or lack of O2 signal to the computer can occur.
Power to the O2 heaters can be measured.
A signal from the O2 sensors can be measured.
The common ground wire for the Heater & the O2 Signal in each Sensor are very important and can be verified.
Typically, when the computer receives a lean indication it compensates by adding additional fuel delivery to the engine.
If the O2 sensors are not working properly, and the computer is compensating by adding additional fuel delivery the engine will run rich all the time.
Are the O2 sensors New?
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Mountain Pass
Joined: Oct 2016
Posts: 172
Likes: 1
From: georgia
The o2 s sensors are new. I'll buy a fuel pressure gauge in the morning and mount it as you say. Do I need to drive it with the fuel regulator hooked up for the test? The fuel regulator is still unplugged and no misfire yet. It also overheated on me today I'm wondering if that's coming from the engine running lean? I also don't have an overflow and will be adding one in the morning when I get the fuel pressure gauge as well.