'86 e-check problems - Any help appreciated

The plugs are NGK BPR5ES. All four had a gap of 0.039" and all were light tan on the electordes and ceramic with no deposits on the ceramic or in the space around the ceramic. The bottom of the threaded steel portion is black but no carbon comes off when you wipe the black part.

The compression test was done with the engine warm but not hot (sorry, I stopped for dinner). Results:

#1: 163 psi; #2: 169 psi; #3: 173 psi; #4 not able to do.

The helicoil that had been put in #4 came out with the plug and I haven't been able to get it off the plug yet.

Thanks for the tip HeX0rz. I hadn't heard of that one.

One more thing. The EGR valve was clean when I removed it to clean it.

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I couldn't get the old helicoil off the plug so I installed a new one. I put some red locktite on it so maybe it will stay in the engine this time (and I did have anti-seize on the plug). I want to wait a while for the locktite to set before running it again. I will put new plugs in too.

I don't have a borescope but in looking in a couple of plug holes with a bright light I can see: (1) the pistons are not black with carbon and (2) there are some visible deposits (even some lumps) on the pistons.

When I do the water into the carb thing do you think I need to worry about freed up deposits plugging up the cat?

Do you still ride a bike? I've got a Yamaha FZ1 myself.

My old VW had a heli-coil come out with the spark plug too. I used a solid threaded insert to repair it. My insert used the same threads as had been already cut for the heli-coil, so I didn't need to tap it. CarQuest has them, likely NAPA as well, even import car shop like for old VWs.

Does the EGR open when vacuum is applied to it? You can test that with a hand vacuum pump.

Actually that's what it was - a solid threaded insert. I put another one back in, but it didn't seal to the head and was leaking some compression past the outside threads of the insert. Luckily I was able to get it back out with an easy-out. The threads in the head are cut kind of sloppy so I will have to put it in with some better sealer. Sigh.

Yes, the EGR does open when a vacuum is applied to it.

Well, I tried the dribble water in the carb thing to clean the combustion chambers. I got the engine hot and put about 14 ounces through the engine at a fast idle. The engine speed dropped about in half with each addition of water. I never did see any big cloud of steam - or any steam for that matter. But the engine and exhaust system were hot and probably completely vaporized all the water.

I pulled the plugs and did another compression test with the engine hot. All cylinders were the same at 170 (except #4 which was down a couple of psi but that was probably due to some leakage past the thread insert.

I still had the dwell meter hooked up when I took the truck out to warm it up - when it is cold it takes about 3 miles of running before the thermostat opens and the temp switch closes. During that 3 miles (running at 2200 to 2400 rpm on the freeway) the dwell was dancing in the teens and low 20's - it never went to 27 degrees. When the thermostat opened (which is easy to see on the panel temp gage because it drops quickly) then the dwell went to zero degrees and stayed there for 20 seconds or so and then jumped to 27 degrees. A bit of acceleration would put it back to zero and the cycle would repeat.

Do you think I should try more of the water stuff or just bite the bullet and pull the head?

Edit: I did another round of the water treatment letting it warm up again for 30 seconds between each introduction of water. No improvement - still a compression test of 170 psi.

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Good day MazdaTweaker.

Yes the engine will stall at idle if I turn the mix all the way in. It gets rough about 1 turn from all the way in and dies just before hitting the stop.

I have already sprayed around the carb base and there are no vacuum leaks there. I will start doing the other checks you recommend.

P.S. I arose from bed this morning fully committed to pulling the head today. Then I read your post.

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More updates:

1. Vacuum Leaks: The line to the brake booster looks good. I pulled if off the manifold and tested it and it holds vacuum. The rubber is soft and flexible but I cut a half inch off the end to get new rubber over the flare in the fitting. In fact the rubber in all the vacuum lines is soft and flexible - amazing for a 20 year old vehicle. I don't think the line to the PCV valve was leaking, but again a cut a bit off the end to get new rubber on the flare (that one was a b*tch to get back on). To be safe I pulled the carb and re-sealed the base gasket. Sprayed cleaner all around the carb/manifold area and no speed change at idle (as long as I was careful to shield the carb intake from the spray with my hand).

2. Grounding BrY wire: Not sure just what "degrade idle" means, but when I ground the wire, the idle drops by 40-50 rpm and stays smooth.

3. Now for the weird: I put the dwell meter back on the BrY wire and got the usual 27 degrees reading. Then I gounded the wire again for a moment with the dwell meter attached just for kicks. The dwell went to 90 as expected and then started reading OK without going to 27 degrees. I was able to adjust the mixture screw to get numbers in the 40 to 50 degree range. It ran in closed loop for about 5 minutes. Then I shut the engine down and restarted and it stayed in closed loop for another 5 minutes until I shut it down again. I have no idea what changed.

Also, with it running in closed loop I was able to crack a vacuum line on the carb (used the one that goes to the vacuum switch & sensor) and the dwell went to zero and stayed there for half a minute until I connected the vacuum line and then the dwell gradually worked its way up again. It never fell out of closed loop, so a pretty good vacuum leak doesn't knock it out of closed loop that easily.

I guess I will go drive it on the freeway a bit and see if it stays in closed loop. I hate it when I don't really find what was wrong.