A&Q about 350Z
Q:
So last night I'm flying down the highway in my 280ZXT....I'm guessing I was doing about 110-120mph..
Started coming up to traffic so I downshifted to 4th (0 throttle), downshifted to 3rd (0 throttle), and while decelerating in 3rd I heard a series of strange noises over the period of about a second. Engine stopped and I pulled over.
Got towed back home.
Here's where it gets strange....when I crank it over, it sounds like I have 0 compression on all 6....but when I floor it I generate 8lbs of intake boost?!?!
Pulled the valve cover...the cam spins.
Pulled the turbo intake/outlet pipes....the turbo still spins freely w/no play, but it has some slight slight bent fins and a couple very small chips.
Compression is as follows.
1- 30
2- 130
3- 130
4- 60
5-30
6-30
All I know is one thing.
**** it....I'm not fixing it this year.
A:
Do you have a BOV or method of recirculating/releasing the pressure built up when you downshift with the TB closed? (turbo is still spinning)
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A:
turbo is not spinning fast enough while downshifting and decelerating to trash the turbo.
You have to remember, all this happend at 0 throttle.
A:
maybe the huge vacuum on the other side of the TB was a factor in your problem? 120mph and pistons pumping the plenum empty of air may have caused something caught by the vaccum to fail.
Missing Turbo bits were obviosly sucked into chambers and could have damaged valves.
Low compression means blown HG, failled Rings, valve sealing problems or head cracks. Pull the head and see what happened.
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A:
But the thing is, the bits that came off the turbo were very, VERY small, and there weren't many....I can't comprehend that there was enough to cause that much damage to 4 cylinders.
I'm not even going to bother touching it....I'm just going to set the car aside for the summer and pay someone to do it this winter.
A:
Well my guess is that you burned the tops of your pistons. Zero throttle + decelerating = lean... The computer shifts lean during this point. So if you were allowing the engine to rev up even with the throttle closed you might have been causing detonation. Esp if you were coming down from 100+ Your engine would be a bit hot inducing the detonation internally. So when you open it up you will see the edges of your pistons melted to the top of the cylinder walls and the pistons may look OK but once you pull them out you'll find that the sides are melted and the rings froze. Usually this happens when you are boosting more than 8-10 psi on these engines stock. I've done something very similar twice. I have pictures somewhere. Just my guess.
ITM has inexpensive OEM replacments. Just like the original equipment. 200bux for a piston set.
Ray
A:
At least blow some air into the cylinders so you know what's wrong. You don't know what shape the turbo was in before the problem so it may not have been a part or affected by the problem. You could also just get another motor & swap in. Much good driving between now & winter.
Anyone can drive a new car.
A:
"Zero throttle + decelerating = lean"
The stock ECU cuts off fuel completely at those RPMs. I doubt it was detonation caused be downshifts.
Can you describe the bits that are missing from the turbine wheel? I doubt it was BOV related because when decelerating like that, the turbo doesn't boost.
Very weird....
Mario
1976 280Z - Dad's Z (turbo swap?)
1978 280Z - Stock Rebuild | 5 Speed | Twice Pipes | Gutted
1982 280ZX - Turbo | MSnS-E | 5 Speed | Large NPR IC
BROKE: Will build computers, webpages, networks, MS units, troubleshoot computers for money
A:
having hooked up a vantage to my O2 sensor during driving I can tell you that the computer doesn't shut off the injectors, it just changes the dwell time while the high intake vacuum takes care of the FPR dropping the fuel amount. Stock tuned the system willl not fire enough fuel in to burn. It will go Ultra lean. Kinda the same way the AB valve works on the carb setup. If something isn't adjusted correctly the system will fail at higer boost.
Or he could have just sucked up some debris and took out his turbo and engine.
Ray
Post Edited (Jul 2, 3:27pm)
A:
get us some pictures of the damaged parts, inside J-pipe, and spark plugs.
Ray
A:
I don't want to look for my FSM... but it states that it will cut off fuel above a certain RPM during decel...
Both the NA and Turbo models....
MS even has it also, it's called over-run fuel cut. It's an emissions thing so that it doesn't keep popping in the exhaust by dumping fuel in it under no load/decel conditions.
Now, if this is a stock ECU ZXT, what RPMs were you cruising at and at what RPM. The stock ECU goes into a burned in fuel map after like 3500 RPM, which is bad if it's running at higher boost then normal.
z32's have been known to do this as well... High speed cruising at high RPM with stock injectors/ECU suddely popping caused by a lean condition, not by a decel.
Mario
1976 280Z - Dad's Z (turbo swap?)
1978 280Z - Stock Rebuild | 5 Speed | Twice Pipes | Gutted
1982 280ZX - Turbo | MSnS-E | 5 Speed | Large NPR IC
BROKE: Will build computers, webpages, networks, MS units, troubleshoot computers for money
A:
..."some slight slight bent fins and a couple very small chips....."
?? On the compressor side?? turbine side?? Or both??
.
If my reply sounds offensive, TAKE IT AS HUMOR !! MUUUUHAHAHAHAHA !!
.
...'77 280 ZEE-EEK.....If it's got Wheels.....It's gonna Cost Ya ! !
A:
On the compressor side.
I know how the turbo looked about 100 miles ago, it was perfect.
I have never, EVER EVER heard of someone melting pistons from decelerating, so I'm going to just ignore that entire post....if such a thing were true there would be huge warnings about engine braking.
I'll prolly drop the turbo and post pics tomorrow.
P.S. the plugs all look fine, there was no evidence of debris inside the combustion chamber, all plugs were a healthy dark tan.
A:
What method did you use to perform the compression test?
72 WooHoo!! In good shape too...
72 Rolling Chassis (RB or LS1?)
80 NA SCCA ST2/CP (Car + Tree = Dead)
82 NA 3.0L the rust monster got it
82 ZXT 3.1L, 25psi! Hit in the right rear. ;(
83 parts car
92 TT Sold! ;(
02 Looking for an '03 made in '02
A:
that is just odd. I am at a loss. a leak down test would do wonders as far as diagnosis at this point.
Im going back to AZ on tues to pick up my roadster and also to pick up my $300 510 wagon (super sweet) I might be your guy for taking a look at it and or fixing it. Im fiarly cheap and I know my way around the L series!!
McAdam
1980 280zx with a mildly ported N47 maxima head, 60mm TB, -C- stamp 256 degree camshaft, and a 2.5inch mandrel bent exhaust. yeah, its quick, and yeah, its a 2+2. NOW with MSandS_E power!
A:
Wow...interesting thread...I am stumped so I am awaiting more input or pictures...
Tys - are you running all stock EFI?
Yasin
Ole Skool "wouldn't have it any other way"
A:
I wonder if you did the damage BEFORE you let off the gas?
-----------------------------------------
12.804 @ 107.26 mph on crappy street tires with Dual SU Powered 2.9L Stroker!
ZCAR.COM member since Aug 1998
A:
Could it haved jumped a couple of links on the timing chain. Maybe a guide broke. Looks like bent valves with 4 cylinders being that low on compression.
What is the compresion when you put oil in the low number cylinders?.
Dexter 260ZT Weee Weeeeeeeeeeee
Rebuilt 280zx engine, n/a efi, added t-3 turbo to n/a engine, n/a intake, turbo injectors, n/a afm, 83 5spd, 3.90 diff, new front end, new seat vinyl, carpet, console, 240z black diamond hatch vinyl.
A:
Didnt try it with oil, not really interested in looking much further into it.
Norm, not sure....I was decelerating at 0 throttle for about 15 seconds before it happened, and when I'd heel-toe going into 4th and into 3rd, the engine made no noises or anything that sounded abnormal.....It was when I was about 1/2 way through 3rd that she gave out.
McAdam, we will have to talk soon....you going on the cruise this coming saturday?
A:
How fast were you going when in 3rd? Did the rpms red line? Dexter's timing chain suggestion seems like the best possiblity.
Check the damper too. When they fail at high rpms, the motors seem to suffer.
Don't know why the turbo fins broke. It cound be a separate event or the cause of the engine problems.
btw why would you heel and toe when decelerating on a highway?
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Post Edited (Jul 3, 9:46am)
A:
It doesn't take much damage to throw a turbo out of balance.
If you can see the damage, it's probably out of balance.
---------------------------------------------------------------------------------
1976 Datsun 280Z 2+2:
-'81 L28ET with 1984 Z31 ECCS
-'81 Turbo snowflakes
-205/60/15 BFG G-Force Sports
-Tokico springs and HP shocks
A:
Blue, wasnt fast enough to redline it....and I was on the brakes, so heel toe was needed to blip the gas & revmatch for a smooth shift.
A:
120MPH tyson ... we do that everyday .. that is not fast ;) however the dapner would not affect compresion .. the chain could be moved ( or out of service ???? i.e. Broke??)
i guess pulling the VC will help
You can sleep in your car, but cant drive in your house
if you are fully in control, you are not driving fast enough!
79 ZXR 46K!
81 ZXT EURO 2+2
83 ZXT
All fine Fastback winnabego's
A:
Do you have BOV or recirculating plumbing? If not then that could be the reason for the turbo's compressor packing it in when you let up on the pedal at high rpms.
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A:
you dont wanna check the compression again after putting some oil in cylinders? that sounds like one of the easiest things to do to check for compression loss.....
Why dont you just sell the car to me?
76 280Z
83 ZXT IC 16 psi STOLEN
86 300ZX RIP
80 ZX RIP
A:
Easiest in my book would be pulling the valve cover ... if the valves would be bent, chain would be screwed .. or something like that it would show .. unless you blew the ringbeds on the pistons from leaning ( do you even control/monitor that closely ???) i mean wide band O2 style?
Tyson it is time for a 3.0 liter turbo and MsS
You can sleep in your car, but cant drive in your house
if you are fully in control, you are not driving fast enough!
79 ZXR 46K!
81 ZXT EURO 2+2
83 ZXT
All fine Fastback winnabego's
A:
Please do a Leakdown test if you're interested in what is damage. You'll know right away if it's intake valves, exhaust valves, pistons/rings. Then it will help you reverse the order of damage to figure out what happened initially.
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James Roraback
1983 280zxt 11.39 @129.38 - FOR SALE
ZCAR.COM member since Nov 1999