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Old 07-08-2008, 10:26 AM   #1
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Red face Strange Rev Limit problem-fixed (changed spark plugs)

Gents,

I've been running an MS v3 as per Braineack's write up in parallel for about 4 months. It is running Hi-Res since 10d and has been pretty solid.

The car is running stock HKS wastegate pressure (MS has been modded for EBC, but no solenoid has been installed as yet). It is a 1990 with the Standard TPS, standard injectors (i know, i have some 330's to go in).

Other than that, I recently changed the pcv valve from the standard mazda one, to a metal can one from an old Ford, but reverted back to the standard one as it held up under boost better than the Ford one

What has been hapenning recently is, after acceleration under a significant load (eg 3rd gear or higher) the MS sort of hits a rev limiter, then starts to idle very badly with AFR's bouncing all over the place.

What is really weird is that the car has been fine for quite a few months and relatively unchanged since MS was first installed, apart from the MS cap mod for Hi Res code (I did it pre empting the rev limit problem rather than having one, so i am unsure if it would be present without the cap in there).

It seems similar to a problem experienced when a fuel filter is blocked or the fuel pump pressure is low, fuel filter has been replaced and fuel pump checked.

The log shows it running smoothly for the first half, then as i pulled onto the motorway and ran the car well in 3rd gear, the rev limit weirdness started and stayed there until i got back home.

I've checked for vacuum, fuel leaks, all wiring. Nothing jumps out at me.

Any help would be appreciated.

Cheers
Nuno
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File Type: zip datalog200807082238.zip (366.5 KB, 55 views)

Last edited by ampz; 07-08-2008 at 11:54 PM.
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Old 07-08-2008, 01:38 PM   #2
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Could you post the MSQ, too? That way I can check rev limiter settings.
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Old 07-08-2008, 02:24 PM   #3
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Could you point us to a specific time reference in that log where the problem occurs? (as a note, if you hit the space bar on the laptop while running, it will insert a reference marker- nice to do just after you've experienced a problem.). Also, a copy of your MSQ would be nice.

One thing I see that's slightly odd is that the MS thinks you're in warmup mode all the time. It's probably not the root cause of your problem, just something I noticed.
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Old 07-08-2008, 06:56 PM   #4
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Oops sorry...
Ok it happens at 575 seconds through the datalog.

One thing that was also done after this symptom first started, was to move the map line to the back of the inlet manifold teed into the FPR.

Also looking at the datalog, is has induced a little more noise in the map line than I would feel comfortable with (used to be baby smooth before, now it is kinda hairy)...

I'm wondering if the cap on JS8 has given up and once charged (after a strong pull) it starts going off?

Cheers
Nuno

Edit: I noticed the warm up thing always staying on too, but the temps are accurate-ish about 1 or 2 deg off... It has always stayed with the warm up on, even pre hires... the mazda ecu is still controlling fans, ac, idle, ps and is sharing the CLT, CMP, CKP, signal. AIT, timing, injection is done by the MS.
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Old 07-08-2008, 11:51 PM   #5
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Red face I should have checked my spark plugs

Gents,

It is fixed, well the misfires have anyway.
Decided to check all the basics, Idle speed (via stock ecu, gnd-ten) base timing (make sure that what MS thinks is 10 degrees is actually 10 degrees)...

Since i have a COP setup, i used a spark lead to extend the cop to the plug... While i was at it i decided to pull the plug just to inspect...

Needless to say the plugs were toast sorry to jump to conclusions... but these plugs i thought were not old (turns out, these aren't the plugs i thought i had replaced 6 months ago when i pulled the motor, the new ones were safely on my garage shelf)

The misfires are gone... all but 2 stumbles very high up in the rev range, which i am attributing to not having the 10000 uF cap for the cops, I'll grab one of them in the near future.

The one thing that Joe brought to attention though, is the warm up not turning off...

Any suggestions?
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Old 07-09-2008, 11:08 AM   #6
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Was it EasyThermed for your coolant temperature sensor?
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Old 07-09-2008, 11:19 AM   #7
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were the plugs visibly worn/damaged? photos if so?
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Old 07-11-2008, 02:47 AM   #8
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Yes, it is easythermed correctly (idle comes down once it reaches 80c with the stock ecu controlling idle, these are from guage readings in MT) and the plugs were looking tired (not burnt like MX03TB but rather dark and the ceramic insulator on them was very brown...

I 'should' have changed the plugs when i assembled the replacement motor 4 months ago (used a spare 92 head i had kicking around)...

I didn't think twice when there were plugs already in the head, I had a neighbour helping me so i thought he put in the new plugs...

I have no idea how old these plugs were they were on the head when i got it (last year) i guess its good they sort of lasted 4 months
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