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Old 09-14-2020, 02:04 AM   #1
adamdrives
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Default 83 245t int. low power

Problem: when driving the car, I can intermittently feel the engine breaking up under any amount of throttle, with no particular pattern other than it happens most frequently in boost or more than 50% throttle. Usually, it has the most power and behaves for the first 5-10 minutes of driving. I can be cruising along at consistent throttle at 65 and feel the engine lose power, then pick back up as normal. It feels like a quick, light misfire that's consistent across all the cylinders. It sounds almost like compression with no ignition, but thats really just a guess. If I increase throttle, it will stay flat until without warning it picks back up.

History: The car has a new WUR, JY fuel distributor, confirmed working frequency valve and pressure switch (blue guy on firewall) and new fuel filter, cap and rotor and plugs. All sensors in the head replaced with new when I was reviving her from sitting. She just passed smog well under all limits. Confirmed pressure switch increases dwell when it sees pressure. I cleaned all the injectors in a bucket of gasoline (which become substantially dirtier after they sat submerged overnight) and she idled better with them installed. I had to run a new ground from pin 16 at the ecm to wake up the FV initially when I was getting the car running, but that wire is still in good condition and terminates on the firewall. Will try moving this, maybe right to the battery.

My suspicions: The FD shaft is binding or otherwise misbehaving internally, this was an issue I had with the original FD that came with the car. I have a k-jet fuel pressure testing rig but I'm not sure what numbers to look for, or if there is a problem with the fuel distributor, what I can do about that besides have it rebuilt or look for another known good. Or, the FV is intermittently losing signal and cutting fuel in boost, and my mixture is going too lean, but then why is it also breaking up at light cruising throttle?. May try to rig up a dwell meter that I can monitor in the cabin. Any other obvious tests I can look into? I've only really gotten into pre-obd2 stuff in the past year and a half, and I'm sure there are some obvious shortcuts I am overlooking. The way the power goes away and comes back also feels like it could be a spark timing issue.
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Last edited by adamdrives; 09-14-2020 at 02:09 AM..
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Old 09-16-2020, 12:32 PM   #2
dl242gt
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That also could be the fuel pump relay having issues. I'd take a good look at the relay and make sure it isn't getting too hot and melting stuff inside. Sometimes you can reflow the solder connections inside the relay. An intermittent main fuel pump can also cause this symptom. I'd put the kjet fuel testing gauge on there and see how stable the system is.
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Old 09-17-2020, 12:02 AM   #3
adamdrives
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I replaced the original dead relay with new when I got the car running, but I need to check fuel pressures. I made a tool to test, but I don't have service info on what pressures I should see.

Diving today, it breaks up through the revs on hard accel, or pretty much at any throttle over 4k or so.
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Old 09-17-2020, 11:14 AM   #4
dl242gt
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breaking up under boost can be spark blowout. That can happen from plugs that are worn out or have too large a gap.

There are three pressure measurements. The system pressure should be around 65-70psi. The control pressure with a cold engine should be around 29psi and rise as the engine warms up to about 54psi. The rest pressure is the decay of pressure with a hot engine that is shut off and it should have about 45psi after sitting about 20 minutes. These are approximate figures I am quoting but should get you in the ball park.
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