Engine woes-just had to walk away

[madkaw]

It hasn't been a very good week and the Z doesn't want to run right.

I have actually been able to find time to work on it, which usually is a problem. But after hours of troubleshooting and working on the car I seem no closer to an answer.It's one of those troubleshooting nightmares that has caused me to walk away before I do something stupid----like give up Z-ing. Symptoms are erratic and only sometimes can I duplicate. I am scratching my head and loosing heart and motivation. I love my Z, but it hasn't been fun lately just working on it while we have had the best weather all year.

I will try and describe my issues-though it will sound vague; I have been around the world and back so my descriptions might seem lucid.

The engine sounds like it has a miss and won't idle as smoothly as it used to. It feels down on power. Laboring might be a good description of the idle.

At first-- cylinders 4-6 seemed to be the culprit. Plugs looked dark and #4 was the worse. But how does half a mikuni run rich? I also had number look dark, but for the most part, everytime I checked 1-3 looked lean or no color.

Now most of this has been idle time in the garage, but those general plug reading were after a drive also. I have seen the plugs 4-6 look both clean and dark during all this troubleshooting, but #4 has been the most consistantly fouled.

My AFR's bounce around quite a bit at first . I have dual exhausts so I only have the O2 sensor in one side or another. At first the sensor was in cylinders 1-3 and the reading were not bad, but erratic, not stable at idle. it would run at 14 and start a bouncing routine and then look lean. I switched the o2 sensor to the rear bank and it was pig rich-like 10.5-11 at idle-hence the dark plugs. I had to turn the pilot screws on 4,5,6, in a 1/2 turn just to get the AFR's to 13.5.

Keep in mind that my jetting is at a known good setting that has worked great before. I've ran these pilots jets and screw settings with no issues before. I have checked floats and they are spot on. I have pulled the covers after running and they are all at the same level. All my pilot screws were replaced and all the tips are in excellent shape.

I suspected ignition or my Megasquirt because of the randomness of the issue. But I replaced all components with a 280zx dizzy and wires and no change. Replaced the plugs too. Ignition timing checked with the dizzy and the megasquirt.

I checked all valves and adjusted as necessary-nothing to crazy.

Vacuum guage only show.ed 12HG at idle taken from a port on my vacuum log. I thought that a bit low.

Sprayed everything down with started fluid and could find nothing.

I removed the complete vacuum log assembly and capped off all port openings. So there is nothing hooked to the intake.

Checked torque on intake bolts and noticed one exhaust flange nut very loose at the very end of the header.

I hooked up a coolant pressure tester to see if pressure was building anywhere --- as in a bad HG. I set the tester at 13psi, the same as the cap and pressure rose slightly to 15psi and stayed. No bubbles in radiator and level seems to be the same. Nothing in the oil.

Compression test done

1-205

2-205

3-205

4-215

5-205

6-210

Not sure what to make of those readings, but cylinder 4 jumps out at me a little. I'm pretty sure these are within percentage limits of each other.

So I proceed to switching out carbs. I swap the 3&4 for 1&2. I run the car and bingo, #2 is now fouled-I found it. #2 would have been #4 cylinder so it must be one side of my carb. So I switch out pilots, and e-tube(which should have much to do with idle). Now #2 isn't fouling, but the engine still idle like sh!t. I should say that I checked all the O-rings when I had ALL the carbs off.

This is what i meant about nothing being conclusive or concrete. I have run and cleaned plugs several times and nothing seems very consistant.

I had to walk away after about 10-12 hours in the last two days. Not sure if a bad intake gasket would cause such issues, or a avccum leak in general. At first my gut said HG, and I'm not totally convinced it's not, but no definite eveidence to warrant pulling the head off.

Valve timing? Well it's not so easy for me to determine this. I have an adjustable sprocket and I degreed this cam in many moons ago. I will have to really ponder on how I will check my valve timing. I have looked down in the hole to see if my chain adjuster popped out or something, but didn't see anything alarming. Could the chain jump a tooth? Unlikely if not impossible, but there is no quick way for me to determine this.

My gut says HG or Valve timing(ignition is safely eliminated), but don't want to go on a gut feeling.

Give me some ideas guys

[jonathanrussell]

Sorry for your troubles. What you are going through can be very frustrating.

So, you previously had a Megasquirt setup managing ignition only, but changed to a 280zx electronic setup to eliminate as an issue? Any possibility that the zx setup has problems also?

Have you done a leakdown test?

Could it be fuel pump / fuel pressure related? I know that the different plug reading results you are getting between your two Mikuni halves seem to logically eliminate that as a problem but....

[madkaw]

I've watched my fuel pressure gauge when i can(in the engine compartment),but that might not tell me if I have a flow problem.Nice thing about the MS is I can turn my pump on without running the car. So I will measure that next to make sure I am getting adequate flow. It makes me think pump when I watched the AFR's slowly bobble to the lean side.

I did discover that my rod linkages needed work. I was just flipping the throttle while leaning over the fender and noticed the levers not at the same exact moment. In fact one of the ball socket ends is worn which allows for movement without throtlle action.

[gogriz91]

I wonder if a Lokar throttle cable swap would help? Most seem to think it improves throttle response.

[240260280z]

I did discover that my rod linkages needed work. I was just flipping the throttle while leaning over the fender and noticed the levers not at the same exact moment. In fact one of the ball socket ends is worn which allows for movement without throtlle action.

I think you found the problem

[zKars]

Ah the old sloppy linkage problem. So many joints, so many places for a little bit of slop and bind and twist to add up to trouble.

Who's idea was multiple carbs anyway? So beautiful and so much trouble. So help me if I ever find him, I'll lock him up and make his food only accessible when a complex linkage of bars, pulleys, turnbuckles and wires are working JUST so. Give him a big flat blade worn our screwdriver as his only tool to adjust it. Couple days here and there of working "ok", but mostly months on end of coughing and spitting stink and bad mileage... Me thinks he will starve very slowly.. Bwaaahahahahahahahahahahaa..

Maybe its time for a matched motor servo on each carb shaft and a drive by wire pedal....

Edited July 21, 2014 by zKars

[madkaw]

Not conclusive or thoroughly investigated , but though it is a problem I don't think it's my overall issue. I only had a little while to play after discovering this, but it wasn't the night and day difference I expected. The jury is still out.

These carbs did/have run beautifully with te response of a sport bike when blipping the throttle. I would never consider cable option as well as throttle feels and works.

Another thing I noticed and don't want to read too much into is the amount of condensation dripping from my exhaust. It hasn't been that humid here but I have been doing a lot of idling. The drips don't seem to ever stop.

Looks like water only.

[zKars]

I hear ya Steve, its not just the linkage, its just making the overall problem seem worse. Just had to get that off my chest.

Water is one of the products of combustion, what you're seeing is not from ambient humidity, or heaven's forbid, cooling system sourced.

Not sure what combustion conditions make more or less water, but it sounds like you may have found a cure for California's drought! Collect that water and send it west!

Hard to imagine many failure modes that cause a too-rich condition. plugging, air leaks etc tend to make things too lean. Spilling fuel due to too high pressure is all both barrel related though.

Hey, you haven't lost any solder out of your bleed pipe hole filling effort have you?et

How about damage to the inner venturi where the main jet fuel comes out?

scrapping the barrel here, how about the "jet block" that the main jet tubes mount in, its a separate thing, and it screws into the main housing, maybe the screws are loose? The screws that hold it in place are accessible from the accel pump cover. Maybe getting fuel in where it doesn't belong?

Loose/missing nuts/screws that hold the main venturi and choke venturi in place from the outside?

Did you replace one of your throttle linkage mounting bolts with a longer one and do a number (crack it, break it, bend it) on the venturi just inside?

Edited July 21, 2014 by zKars

[madkaw]

Jim,

I appreciate all the input-truly.

Not sure that isn't one of those deals that I have made worse by trying to fix the wrong thing with an adjustment here or there.

I will eliminate the possibility of a faulty fuel pump when I get back to town . I will do volume test there.

I also need to make sure any linkage issues are resolved.

This has just been a total kick in the balls for this summer. Too many nickle and dime issues already and this just takes all the fun out of my hobby. Thought I would be at the dyno by now and pushing forward on my custom FI project.

Hopefully walking away will reset my attitude. I about have to take a week off since the family is going to CA for a week.

[madkaw]

Your mention of solder was noted and it has been on my mind. I know my bleed pipe alterations are still in tack, but wonder if loose solder from previous attempts have made their way somewhere not good. I tried to be careful but might have gotten sloppy and not cleaned up properly and now have solder blocking a passage. I'm not too far from breaking the carbs all down anyway.

Cursory inspection shows clean as a whistle

[madkaw]

So I pulled off the carbs and put compressed air to everything. Didn't see anything in these carbs that is causing my issues. Put them back on and ran the car around the block and still bad.

Tested the fuel pump and she flowed good.

Linkage was adjusted up and it runs the same. The issue I get is from cylinder to cylinder on the same carb-not a linkage issue. I checked the butterflies and they are in sync-measured with a feeler gauge.

I pulled the intake hoping to find a bad intake gasket, but it looks great.

Now it's decision time-pull the head or not. Compression is good on 3&4 with a compression tester. Really need to do a leak down, but don't think I have a compressor that will put out enough pressure. I need to check into this.

Visually, 3&4 intake side of head look worse then all the others. The inside of the intake runners(inside relative to each other) have a bunch of crap on them. i will try and get a pic, but it looks like oil that is coming from the guide. That's just a wild guess.

[djwarner]

You sound like you re-installed the carbs in the same position. With multiple units installed, a good trouble shooting technique would be to swap two carbs and see if the trouble followed the carb or stayed.

Since you mentioned it your first post, it points to the carb. Did something happen to change your mind?