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cylnder compression


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i own a 1975 280z coupe with the l28 fuel injected engine, and i just did the compression test, and i was wondering if these readings are good or not?

 

Back of car 128/130 psi, 135 psi, 135 psi, 145psi, 135 psi, 140psi Front of car

 

i am not sure, but did i blow my head gasket? any input would be greatly appreciated. Thanks for all of your help and support.

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I wouldn't think you had a bad head gasket. All a little on the low side. Maybe your guage is off. BUT,....... they are all within 10% (very close) of each other which is a good thing. Is there a problem you have, or are trying to solve????

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I wouldn't think you had a bad head gasket. All a little on the low side. Maybe your guage is off. BUT,....... they are all within 10% (very close) of each other which is a good thing. Is there a problem you have, or are trying to solve????

it is very hard to start. and exhaust is comming from under the hood. I have to ctank the motor for about 2 minutes before it starts to stumble, and then when i pump the gas pedal it starts to fire, and run.....but with alot of exhaust. so do i need a new exhaust gasket between the headers?

There is no coolant in the oil at all so i thought the gasket blew out on the drivers side, because nothing is pushed out on the passengers side. and i am using new Snap On tools. what should the compression be by the way?

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Header leaks are common. So you MAY need a gasket. That would not cause a hard start. I have not used it, but there is such a thing as the "fuel injection bible". You need to approach your problem analyticaly. You need a manual. Check the resitance of your coolant temp sensor. Very important.....as are other things..Good Luck.

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Header leaks are common. So you MAY need a gasket. That would not cause a hard start. I have not used it, but there is such a thing as the "fuel injection bible". You need to approach your problem analyticaly. You need a manual. Check the resitance of your coolant temp sensor. Very important.....as are other things..Good Luck.

thanks....and i have i that, and the haynes manual...the only thing i cant find is the fsm for a 75 280z

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Adjust the valves. Bump the timing to 14-16 degrees. Run some Seafoam thru. I'll bet your numbers increase by about 10 psi. Take the car out on the highway and run it HARD for an hour or so. It'll run much beter afterwards. These EFI cars tend the run rich with age. That in turn causes sludge, carbon and sticky rings---which will lower compression. Puttering around town and lack of use is the WORST thing for EFI Z Cars. Fresh oil, some meticulous routine/preventative maintenence and some hard use (NOT abuse) will work wonders for your car!

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On a very good motor the cylinder pressure will be at 180 PSI or higher. We checked my old car I sold back to a friend at 200,000 miles and your numbers were like what we got. They are a little low but your car should run fine. It does sound like a fuel injection issue you are having.

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Powerglide's right, sounds gunky, and all of my older Z's had the same issue, they all ran on the rich side. Once you have all the exhaust leaks covered, (don't forget to check the bend at the bottom of the downpipe!) and clean out the rings a little, make sure your gas mileage is right. It should be somewhere around 21-27 mpg depending on your driving. If it's noticably lower, that's a sure sign that one of the computer inputs to the fuel injection system has failed, and it's running default. Last one I had was the cylider head temp sensor, overnight I went from 23mpg to 14mpg. And no more running down to the corner market! Make the drive at least 5 miles to let the engine warm up and run in closed loop mode every time you drive it, that'll help with the build up of crap from the rich fuel system. That fuel injection bible really is helpful if you don't know EFI.

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If you are getting good compression (which you are, just maybe a little warn out rings), i would check to make sure that all the injectors are working properly also and not dirty. Mine had bad injectors (very bad pattern and streaming) and it was making it very hard to start and poor performance at low rpms.

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Is it possible for the stock computer to be unning on a closed loop?

 

it is all stock right now so is there the possibility i could have a few bad cylnder rings? or could this be because i have a bad intake/exhaust gasket....befroe all this happened....i was goin 120, at 5000 rpm, and when i got home my car was overheating, and after it cooled off i started it the next morning, and exhaust was comming from under the hood........so idk what happened

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