Compression test is not correct

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cecati14
Newbie
Posts: 2
Joined: Wed Sep 05, 2018 2:25 am

Compression test is not correct

Post by cecati14 » Fri Jan 10, 2020 2:47 am

Hi guys, I´m facing a Starting problem with a 4 cylinder Chevrolet car, TBI, 1.6 Lts, gasoline. Nowadays sometimes after cranking the car runs during a short period perhaps up to 1 minute, then stop. The problem appeared or was more noticeable three or four months ago, at that time the car started with no problem most of the time and just rare occasions, one important issue is that sometimes the engine while running on the road suddenly went off. Time has passed and as I wrote before, starting the car is not possible. I have tested all the issues related to NO STARTING tests such as CKP signal presence, Ignition coil performance, timing engine, injector, fuel pressure, clogged exhaust, immobilizer, PCM, etc, etc. I measured compression with a pressure gauge and results were OK (135, 130, 135, 140 PSI) however I used "just in case" my 4425 Picoscope with "PICO DIAGNOSTICS and the results were Cylinder A: 100%, Cylinder B: 100%, Cylinder C: 67% and Cylinder D: 92%.
With Pico Diagnostics results I thought I have today a compression problem but not too severe to never crank, based on these results I randomly unplugged 2 spark plugs and ran again the Pico Diagnostics and 100% 95% 97% 100% were the obtained compression values! Please notice that I had unplugged 2 spark plugs!

Regardless of my compression problem, Do I have a problem with my PICO DIAGNOSTICS? The version I have is: 1.9.5 build 2724.
Thanks in advance.

ben.martins
Pico Staff Member
Pico Staff Member
Posts: 184
Joined: Tue May 16, 2017 1:02 pm

Re: Compression test is not correct

Post by ben.martins » Fri Jan 10, 2020 11:19 am

Hello Cecati,

Thank you for your post.

You are running quite an old version of PicoDiagnostics. The current version is 1.14.0.4585. I think the best thing to do is get the software up to date which you can download from the website - www.picoauto.com/downloads.

If you could also upload the capture you had where the plugs were removed, we can start to understand and explain why you are seeing the results you are getting.

Kind regards

Ben

cecati14
Newbie
Posts: 2
Joined: Wed Sep 05, 2018 2:25 am

Re: Compression test is not correct

Post by cecati14 » Fri Jan 10, 2020 4:41 pm

Hi Ben, thanks for your answer. I'll up to date PicoDiagnostics version. I have the pddata file with the capture of the problem and is a good suggestion to send it. But I don´t know how to add it here. Is there a tutorial on how to?

Regards,
Cecati14

Technician
TwoWaves
TwoWaves
Posts: 526
Joined: Thu Apr 24, 2014 8:32 pm

Re: Compression test is not correct

Post by Technician » Fri Jan 10, 2020 11:02 pm

Cecati14,

When you click the reply button this box appears that I'm typing in. if you look at the bottom where it says options and attachments, click attachments and follow the instructions. I've found when uploading that unless you watch the attachment button closely you may think nothing is uploading, but careful observation and you'll see a line appearing horizontally underneath the word attachment. When it gets to the end depress the preview button and then press submit.

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