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Username Post: 3.1 GM engine,low compression in 1 cylinder        (Topic#354687)
Andy J 
Posts: 42

Age: 68
Loc: east central Mississippi
Reg: 10-29-15
01-02-19 03:24 PM - Post#2756368    

Maybe someone here can offer an answer.3.1 GM V-6 engine,used in many GM cars,has low compression in #1 cylinder,missing at idle and causing a P0301 code.
A little history:I bought this'02 Buick Century with a bad engine,to be fixed up as my daily driver.The car is like new,inside and out.Anyway,I bought a remanufactored long block,put on all the bolt-on parts,and dropped it in.Fired it up and it missed at idle from the beginning,throwing the code.The car had been garaged for 4 1/2 years,so I figured the fuel injectors were probably gummed up.I ran it for a month or so and took it to a shop to get the A/C fixed.The mechanic,whom I fully trust and have dealt with for years,said,"I think you have a compression problem",checked it out,and indeed was the case.I forgot to mention the engine runs like a top at 900rpms or higher.

He tested everything he thought might cause the problem and found nothing wrong.I called Spartan engines,who built the engine,to see what to do.They wanted to have the man tear down the engine,at my expense,to find the problem.He won't do it,because he already charged me $385 for the tests,which I'm good with.Spartan won't pay for anything,unless their parts or workmanship is at fault.Their warranty isn't worth a damn.When I saw the engine was assembled in Mexico I should have demanded me money back.Don't EVER deal with this sorry censored company!

Back to the engine:the mechanic thinks the engine has a mismatched piston or rod that isn't coming up to full deck height,causing the low compression.#1 cylinder is 125psi,the rest are 200psi.He said you'll probably have to live with it,seeing how Spartan engines won't help with anything.I'm PISSED,to say the least.

So,do any of you have an idea why this engine won't run right?


Frequent Contributor
Posts: 2147

Loc: Lake George, NY
Reg: 11-11-15
01-03-19 11:34 AM - Post#2756473    
    In response to Andy J

A leak down test should be done in that cylinder, if it is a valve, you would hear it in the intakes or exhaust. If you hear air in the oil filler area, than it is a bad ring or piston issue, I have also seen rocker arm bolts pull out of the head on theses engines. Pin it down and you have a case.

Andy J 
Posts: 42

Age: 68
Loc: east central Mississippi
Reg: 10-29-15
01-03-19 12:18 PM - Post#2756480    
    In response to Shepherd

Thanks for the reply.The mechanic did all the tests you mention.Everything was well within factory specs for this engine.He checked the injector on that cylinder and ignition components.That is why this is so puzzling.

He believes that cylinder has a mismatched rod or piston,that at TDC isn't coming up as far as the others,causing the low compression condition.He said he's seen this before and it displayed the same symptoms.

I've already got more money in the car than it's worth.Aside from the engine,I've had to buy new tires,fuel pump,battery,and a new A/C compressor.An engine tear down,plus being without a ride for a while,isn't doable at this time.As I said earlier,the engine runs great above idle,so I'm just going to drive it until I can come up with a better plan.

My advice to anyone needing a new motor:don't deal with Spartan/ATK engines.Assembled in Mexico and their warranty sucks big time.

Live and learn.


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