ShipEngr

So I just bought my first Zcar last week. Its a 1983 Turbo Coupe with a 5spd and 94,000 original miles. The previous owner had done alot of work (with documentation) that included replacing injectors, sensors, hoses, brake calipers/rotors/lines, transmission fluid, etc. Given that and the fact it had relatively low miles and it drove well I assumed it to be fairly mechanically sound. Interior was all there with the normal sun-rot you find on a burgundy 280ZX. Body is pretty straight with very minimal nicks and little rust. I snapped it up in a fit of excitement for about $6000.

Here's where the night terrors begin. I've had minor issues with rough idle when starting for the first few minutes and discovered in the 1st week I owned it that fuel economy is a straight up problem. (~10mpg). I had a compression test performed with results as follows:

# 1) 100psi
# 2) 100psi
# 3) 100psi
# 4) 100psi
# 5) 100psi
# 6) 105psi

Wet compression raises the figures up about 10psi. To me the wet test indicates that the piston rings have normal wear but as I know the stock spec for these engines would be dry compression at 143psi. I spoke to the mechanic at Awesome Z in Houston about a top end rebuild to clear up this problem but in his opinion compression figures such as these would require a full engine rebuild, for which he quoted $3500-7500 for.

Its really unfortunate because I had planned on making this my daily driver for the next few years until I get another car and can spend the time/money for a full frame off restoration. Now I am afraid driving this thing in its condition might lead to total destruction of the engine and require an engine swap, which fully defeats the purpose of restoring an original vehicle with matching serials.

Any advice, guidance, or opinions greatly appreciated.

zxguy1986

Unless the existing engine has serious sentimental value for you, just swap it out - for probably half of what he quoted for a rebuild. (Who does a $7K rebuild on a $6K car??)

Plus, you already know what's good and bad on the existing. You get to cannibalize the good and either re-install, store or sell all those parts. Good deal! IMHO

Skully

I would do a leakdown test before considering a teardown. The cylinders are close to each other, and a wet test didn't make a huge difference (usually if it jumps wet, its the rings). I might wager a guess as to something with timing or top end.
Good luck!

Zuphoria

Who at awesome z quoted you that? Doug (owner) is a straight up guy, does good work. 3500-7k sounds like something you heard but wasn't spoken, that's a retarted figure. If you have 100psi across all cylinders on a dry test. And a wet shows little change... I would be looking into checking the cam timming and perform a LEAK down test after you assure the timming is correct. Get the fsm from xenon and if you have any mechanical exp check the crank to cam timming using the oblong grove method.

ShipEngr

It was Doug that quoted me but it was a quick over the phone ballpark.

Thanks that is good advice. I checked the air regulator and ctms both with satisfactory results, I need to pull off the regulator to visually see the flap operation but resistance is okay if high (~125 ohm) and interrupting the flow while cold decreasing RPM and when warm no change.

I'll read up in FSM but what would cause an inaccuracy on cam timing? A worn chain or cogs or what? The chain has never been replaced to my knowledge.

rogerz

After 35 years at sea I would say you violated the first warning ever given to younguns. If you see it, you like it, and you are drunk -- DON'T BUY IT. 6 K for an S130 you are out of your mind spend your payoff on wine women and song. I wouldn't worry about the compresion your problem lies elsewhere. All the Cylinders are close so it should run pretty good. Either your AFM is off and you are burning rich or your fuel pressure is off or you have a large vacuum leak somewhere. If I remember right my 83T ($200) compression numbers weren't far off that and she ran great. Is the turbo even boosting? Start looking elsewhere than compression for your problem. if that is a true 94K on clock then it is just barely broken in. my 83 had 240 K. My 81T had a bit over 2K. The L28 is a brute and fairly bulletproof.

Zuphoria

The timing chain it self is probely not the problem, but yes there are guides and a tensioner that is oil driven that can ware out. If you just set the engine at TDC and pull the valve cover and look at the timing marks on the cam sprocket you will know instantly if its off. There is nothing electronic on a z that can cause low compression, its all mechanical. But like rogerz said, 100psi....the car should still run ok.
Factory Compression on a turbo 7.4.1 engine is 140psi dry

ShipEngr

Well good news is I pulled the valve cover off and chain is real tight and guides look just fine. Unfortunately the largest metric socket I have is 24mm so I wasn't able to check TDC so ill have to go pick one up and check it, then I'll take it somewhere and have a leak down test done. I boogered up the cover gasket a bit so I'm gonna get a new one and replace it when I do that.

Guessing on a vacuum leak somewhere is part of my issue. I know the injectors and fuel pump were replaced but with non-oem and probably cheap aftermarket parts. Turbo is boosting with a lot of good torque above 2.5k rpm, just a little hard to start and rough idle for the first 30seconds or so. Never stalled or hesitating under load.

Zuphoria

Post some engine pics, maybe someone will notice something wrong, or out of place. Take a couple.

Zuphoria

Any update on the car?

Zuphoria

https://www.zdriver.com/forums/240z-...e-l28et-30099/