A few newb questions for my '86 NA:

1. FSM says to warm up the engine before doing the compression tests. I don't have tons of experience pulling the plugs with all the top end stuff attached, so I'm afraid the engine may be pretty cool by the time I get #6 out... how warm is "warm"? If it takes me 20-30 minutes to pull the plugs (yeah, it could), and another 5 minutes per cylinder, I'd be close to an hour before getting to #6. That doesn't seem too long to me, but just wondered...

2. Assuming I find a cylinder with low compression, it raises several more questions:

• should I be doing the FSM procedure of putting a small amount of oil in the cylinder to see if that helps, or go straight to leak down testing?
• I've seen videos that show using a tool that gauges how much leakage you have, but I can't really see the benefit if I have already decided I have unacceptable compression. I'm mainly interested in knowing where the leakage is going. Is there another reason to use the tool? It regulates down the air pressure, so I assume that may be one of the benefits. I read online that using the tool can indicate variability in leakage from one cylinder to the next, and the gauge indicates percentages which may be used to judge whether that's acceptable or not. The only reason I could see this being helpful would be if the compression test was not done first.
• If I use straight air pressure, would assume something in the 40-50 psi range should be enough... any advice?
• I've tried using compressed air once when I was removing the valve springs. I had read that was a way to keep from dropping a valve. I hand cranked until the piston was at TDC, but when I put air pressure on it, it moved the piston to the bottom of its stroke... thought I had the transmission in gear, so that was a surprise. It's been a while, and I may have done it wrong... just wanted to make sure that's the right way to keep the piston from moving... don't really know any other way, and it's what I've read as the procedure.

 

you are chasing rainbows. Why are you assured that your compression is bad? even if you find a bad cylinder you are looking at engine tear down and rebuild. Just get the compression readings and go from there. forget the leakdown test you won't learn anything unless you are building a competition engine (and if you are then you already know what you need to know). You will find it much easier to pull the plugs if you invest in this little darling.



take out the two maybe three screws holding the throttle body down makes it much easier to do #6 the others not much trouble. First be sure you blow out the well in which the plugs sit they are great traps for any dirt or screws dropped on the engine. Have all the plugs out before you run the check makes the load on the starter that much less. Have new plugs ready to go plus a set of wires (Magnacore best but Bosch or NKG okay), new dizzy cap and rotor. you need someone to turn the key or rig up a remote button for the starter so you can turn the engine whilst obtaining readings. My handheld gage with a rubber tip has worked well for the last 40 years. you really don't need much else unless you are a far better mechanic than your post would indicate.

here is some stuff to do that is a lot more important than a compression check unless the engine is running so bad it needs a rebuild anyway

Get your battery load tested. Be sure you have clean, tight corrosion free terminals on both ends of your battery cables. Be sure the ground (negative) cable goes to a bolt into the frame before going to the starter. grounding through the starter is not a reliable connection. Z's don't like low voltage. causes the electronics to act funny. it is possible to have enough amps to crank but not enough voltage to run the electronics. If you have one size fit all cheapo clamp on terminals they are a problem waiting to happen. Usually on a rainy night around Oh Dark Thirty.

Clean the connectors for the maf or afm, ecu and tps. Deoxit by CAIG is probably the best connector cleaner on the market. spray with CorrosionX after cleaning and before putting together this will help prevent any further corrosion. DON'T USE DIELECTRIC GREASE.

Replace outer tie rod ends, and ball joints. replace the bushings with poly (don't forget to lube them as directed unless you like squeaky things). New shocks. Get new boots for power steering. all those things will make you think you are driving a different car. doing them piece meal is a waste you won't see a great improvement until you do the complete job. You need to get the car realigned after messing with the front. Have your tires in good shape and rebalance. Rear bushings nice too but more work and you won't notice as great an improvement. Rear shocks also because if the fronts are gone so are the rears. if car squats when you jump on the gas the rears are gone.

 

Well thanks for all that...

I don't know I have low compression, I have low power and want to do the compression check to see if that is a possible source of the problem. I am burning oil, or running terribly rich, because I get smoke from the tailpipe but cannot determine what color it is... Most likely it's from oil consumption, but who knows.

Car has been a garage queen for a couple years now. I did the timing belt and associated maintenance items (incl. CHTS), replaced plugs, wires, distributor cap & rotor, replaced valve seals (on advice that they might be the source of oil), replaced fuel pump & FPR, did a POR treatment on the gas tank. Sent the fuel injectors out for service and also did the PRW-2 conversion.

All of the above (except the seals) was on solid troubleshooting or as a normal tune-up type thing. Not getting any ECU codes, so mechanical was my next line of attack. Car has >150k on it, engine has never been overhauled as far as I know.

Unrelated to the engine, but to affirm your other advice... I have done a complete refit of front end suspension bushings with poly as well as having the steering rack overhauled (vs. buying cheap reman). Also replaced the rear shocks, and new tires as well.

Need to chase down the electrical stuff a little more. I've cleaned most of the connectors you mentioned, but not with the product you recommended. There was some slight evidence of corrosion, but I live on the Gulf Coast so I'm sure there's more where that came from. The electrical ground wire is connected to the firewall where the OEM negative battery cable connected.

All of that said... any answers on my original questions?

 

if it has 150k and is original it has many things not quite right internally .
clogged oil cooling holes in the pistons pitted valve faces where they hit the seats i could go on and on .
I recomend a completely cold ( not started for 4-5 hours not even for a sec.) compression test and the cyl. should be to 80% of specs with 2 pulses .
40psi is way over leak test compression they recommend 10-15lbs , some as little as 8-12.
In the shops I worked you can see the leakage but never hear it ( I could barely hear a wrench drop ) also you need a expensive air regulator for the low pressure about 50$ now I bet .
If you see low compression on a cyl then if you want you can hook air to it to see/ hear where it is leaking
I'm not telling you to do it but some drill a 1/8" hole before the CC ( then weld back )to see what oil is burning the CC will burn up even moderate oil burning almost instantly ,or start it up cold with you standing behind it smelling for oil .