Engine lost compression

Sultan
Club4AG Regular
Posts: 15
Joined: Sun Nov 22, 2015 9:57 pm
Location: California

Engine lost compression

Postby Sultan » Sun Mar 11, 2018 7:11 am

well my engine recently got rebuilt new pistons and rings and we checked compression
and was 200psi across. I took it to a shop to get the timing sorted out they set it to 15degrees
at idle and was running fine, a couple days later I took it to the same place to get a base
map on it, the tuner was setting it up on the dyno but I could help but notice the headers
were glowing red hot so I brought this to his attention and he said its okay, I have very little
knowledge about engines and how they should be set up but this seemed off but I didn't think
much of it because I assume he knows what he's doing and of course has more knowledge a
nd capabilities about engines and tuning.

Long story short the car was running like that for about a month to break in the engine,
the engine would always knock slightly at the lower revs especially when moving from a
standstill again I brought this up and he said its to do with the compression im running which
is about 12.2 but im using 98 octane gas and he said not to worry because the knocking is
happening at the lower revs so it won't cause any damage.

The day came to finally get the car tuned so we headed to the dyno and he tuned the car,
again cherry red hot headers, I mentioned this to him again that this doesn't seem right
but he insisted it was okay. About 2 hours later of constant hard pulls on the dyno the car
was done being tuned. After that he seemed concerned because he could only advance the
timing on the ecu to 16degress after that the car wont make any power also the car wouldn't
make any power passed around 7900rpms which to me seemed strange because I have big
cams that should be making power to 9000rpms, so rev limit was set to 8500.

He was also using knock ears and assured me the car is running fine with no kock or
anything. He told me I must be using very high compression pistons somewhere like 13.7
which I told him is ridiculous and there's no way it can be that high Toda pistons are
advertised at around 11.7 but with my thinner trd head gasket bumps it to 12.1-12.2.
Also I know for a fact my head has not been skimmed or anything.

A couple days later I was doing a hard pull and I could here detonation happening in the
engine at around 5600rpms under full throttle so I backed off and took the car back and
told him what happened. He then finally decided to check the timing again and he mention
that it was really advanced at idle so he fixed it again and like magic no more glowing headers
again and knocking at idle seemed to go away. I was really annoyed because of this and I
asked him to check the pistons with a small camera and what do you know pistons 1 and 2 had
detonation marks on them nothing to severe but again noticeable also cylinder 1 had some
scratch marked on the walls which I could see from the camera. also there was a lot of carbon
build up on the pistons .

I asked him to do a compression test and it came back as 172 175 199 200, the pistons with
lower compression were the ones which had the detonation marks on them. He said that the
detonation marks won't lower the compression and started to point towards the engine builder
making a mistake or something. I didn't believe this because it was built by a reputable shop
who has built hundreds of engines in the past and not one has failed to date. I was extremely
displeased about this and he said he would tune my car again for free I told him I would think
about it and left.

I don't know too much about engines or tuning but I did some research and found out that with
lower timing like that 16 degrees and tuning the engine at high rpms on the dyno would cause
the spark to fire when the piston is already far down on the cycle and combustion happening in
the cylinder which could burn off the oil on the cylinder walls and cause them to be scratched?
Also the unburnt fuel from the low timing would make its way out the exhaust valves and burn
in the headers which would explain my situation.

Im not sure what to do know and whos at fault the tuner or the engine builder and I don't know
how to proceed with this maybe someone can help me and explain what happened to my engine.
its still working fine and all but its no longer 100%

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totta crolla
Club4AG Expert
Posts: 493
Joined: Tue Mar 26, 2013 5:21 am
Location: Oxford U.K

Re: Engine lost compression

Postby totta crolla » Sun Mar 11, 2018 11:47 am

If 16°is maximum ignition timing advance you might want to check camshaft timing, you will probably find that the inlet camshaft is too far advanced.

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jondee86
Moderator
Posts: 2279
Joined: Fri Jan 11, 2013 10:21 pm
Location: Wellington, New Zealand

Re: Engine lost compression

Postby jondee86 » Sun Mar 11, 2018 2:44 pm

In general, when the car is on a dyno, a tuner will advance the ignition timing until
the engine stops making power and then back off a couple of degrees. At high rpm
ignition timing will typically reach something like 35 degrees.

On a high compression engine with big cams, because of the lack of manifold
vacuum at low rpm's idle rpm will be higher that stock, perhaps around 1500rpm or
whatever it takes to get a stable idle. And because big cams don't work that well at
low rpm's, getting the car awy from a standstill without provoking knock requires
a few more revs and a bit more clutch slipping than with a stock setup.

The tuner has full control of ignition timing with a programmable ECU, and if the
engine stops making power well short of redline, that is not something that can be
fixed by adjusting the ECU. As stated above, the problem may be with the camshaft
timing or perhaps with the trigger settings in the ECU.

To investigate properly, you will need to check everything to do with cam timing...
- Cams installed/timed to the manufacturers Cam Card recommendations.
- Adjustable pulleys set correctly and tight (not slipped from original settins).
- Cam tensioner tight and no possibility of timing belt having jumped teeth.

Then the synchronisation of the ECU with crankshaft TDC needs to be checked to
endure that when the ECU is delivering timing at 15deg (or any other value) the
spark is actually occurring at 15deg BTDC on the crankshaft timing scale. The kind
of situation that you have will need to be resolved with hard facts. Otherwise you
will end up in an infinite loop of buck passing between the builder and tuner.

Cheers... jondee86
Give a person a fish, they eat for a day. Suggest they search before posting, and they learn a skill for a lifetime.

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