intermittant skipping

[tabaka45]

1980 280 ZX, 134,000 miles.  I let the car sit for a while and the fuel went bad.  Car ran terribly.  Ended up replacing the injectors (with Bosch injectors), fuel regulator, fuel filter, distributer cap and rotor, spark plugs and plug wires.  Now I have an intermittant skip that feels like somewhat like a misfiring plug or wire--but they are new.  Someone told me that this same thing can be caused by a bad egr valve or perhaps some other part of the emissions system.  Sometimes it will run several miles without an issue and then start skipping for a while.  It seems to stop if I accellerate hard.  The valves have been adjusted and compression is even at about 155 on all cylinders.  Any suggestions on how to run down an intermittant skip.  Once I resolve this I plan on having the body and inside fully restored.  

[Zed Head]

28 minutes ago, tabaka45 said:

1980 280 ZX, 134,000 miles.  I let the car sit for a while and the fuel went bad.  

How bad and how long?  Sticky valves, rusty parts, etc. can happen if it's been sitting for years.  My original engine ran better after giving it a hard run.  The valve seals were worn and I think that they maybe softened up for a short while after a good beating, plus clearing out the oil in the combustion chamber.

Anyway, a year sitting is a lot different than ten.

[tabaka45]

While it had been setting for several years, I've driven it every 4 or 5 months about 10 miles.  The last time it set a little longer, probably 7 or 8 months .  I had stabilizer in the gas but it was still pretty old and I had to drain it and refill.  The gas smelled terrible, so I'm assuming that had something to do with the injectors getting gummed up, or at least I thought they were.  Now I'm not so sure.

[Reptoid Overlords]

Does it seem more prominent at a certain RPM range? I had a strange misfire just under 2k at coast. Wide open or over 2kRPM it went away. I ended up adjusting the throttle vane switch per the FSM and it went away. Its an '80ZX.

 

 

[Reptoid Overlords]

Also, I noticed I could reproduce it with the engine idling, and with my hand slowly operate the throttle until it started acting up.

[tabaka45]

It occurs at any rpm.  Someone suggested I test out the EGR valve which I have to read up on.  To me it still feels like a mis-firning cylinder, but with all new injectors, plugs, wires, and distributer cap and rotor that seems to rule out electrical ignition issues.  Compression is about 155 on each cylinder, so I assume no issues with the valves.  I've never dealt with emission systems with all the valves, hoses, etc., so I'm sort of lost as to where to start.  

[Dave WM]

The EGR would most likely have an effect at low RPM you can test it by manually lifting the diaphragm while idling. You said you installed bosch injectors? were the new? I have a recent video of me trying to "see" the misfire using one of those clear spark plugs. I have not done anything else on the miss (mine is idle only), but if I had to guess it was a bad injector that does poorly at low flow rates. Not saying that is your problem since you say it happens at any RPM.

If you can make it happen you could try a load test, pulling one spark plug cable at a time and see if any one has less effect on the miss. try to narrow down the issue. Just don't shock yourself, the ungrounded spark will try to find a path, I would use those long plastic cable pullers designed just for that, and then hold the open plug end near the block so the spark has somewhere to go.

Edited September 25, 2017 by Dave WM

[Reptoid Overlords]

Probably a shot in the dark, but check the connections at your ignition control module. Make sure they are tight and clean.

[tabaka45]

21 hours ago, Dave WM said:

The EGR would most likely have an effect at low RPM you can test it by manually lifting the diaphragm while idling. You said you installed bosch injectors? were the new? I have a recent video of me trying to "see" the misfire using one of those clear spark plugs. I have not done anything else on the miss (mine is idle only), but if I had to guess it was a bad injector that does poorly at low flow rates. Not saying that is your problem since you say it happens at any RPM.

If you can make it happen you could try a load test, pulling one spark plug cable at a time and see if any one has less effect on the miss. try to narrow down the issue. Just don't shock yourself, the ungrounded spark will try to find a path, I would use those long plastic cable pullers designed just for that, and then hold the open plug end near the block so the spark has somewhere to go.

I have pulled the plugs wires one at a time and they all seem to have the same effect.  The plugs, wires, distributer cap and rotor are new so I'm assuming they are ok.  However, I may get a known good wire and another plug and switch them out one at a time.  

My "skip" is intermittent and occurs at all speeds. It's gone several miles without a skip and then start skipping a lot.   It really feels like one cylinder is dropping which could indicate a bad wire, plug or rotor, but again they are all new.  The troubleshooting section of the Haynes manual says that a bad EGR can cause the same symptoms, so that's my next test.  Probably next week due to schedule issues this week.

 

[tabaka45]

15 hours ago, Reptoid Overlords said:

Probably a shot in the dark, but check the connections at your ignition control module. Make sure they are tight and clean.

I'll recheck it, but I think it's ok.  

[tabaka45]

By the way, did I ever mention that I hate electrical problems!

[Reptoid Overlords]

Did this ever get resolved?