Home Project 1MZ-FE VVTi Conversion

[rainen]

Just did a quick look over the engine tonight. All dry and no signs of any external oil leaks. Oil level is on the full mark. Front three spark plugs are the right colour. Coolant level is normal and red so it's got the right stuff in it. Engine note through the exhaust sounds nice and smooth. So overall I'm really pleased with this purchase and should be a good engine to put into the MR2 that I'm yet to buy. Given the mileage these engines run for 86k is young. Most of the current advertised RX300's have north of 120k. Will post next when I've started to de clutter the engine bay a bit.

[cdwood2010]

Just bought myself one of these bad boys as a daily driver. Theyre awesome vehicles.

c.

[rainen]

So just wanted to get some benchmark data from the engine so that I have a reference point to at least to prove to myself that it works fine. We have no stored codes and just pending P0172 too rich Bank 1. Thats down to crap plugs as I had the same code pending on Bank 2 but I swapped in some spare decent ones and that cured it. No worries with that at this stage. Both of the AFR's are switching and the voltages are in the right ball park. ECT working OK and RPM at 80C and above drops to idle at around 700. The short term fuel trims are around the 0 mark for both banks with the long term around -25 for both. Data looks good, just going to give the engine bay a quick degrease and powerwash later in the week then its onto the removal process. For interest i'm going to follow the Haynes manual engine removal procedure so I can have a little bit of structure ( as opposed to start taking as much as possible off and hope!). Hope to do an update with each step and pictures as necessary. Nigel

[Paul Woods]

Those long term fuel trims are far too low, that is what is triggering the "too rich" codes, so you need to establish what is causing the high negative long term fuel trim values.

[rainen]

Any recommendations on areas to look? Internet talks about a few things like MAF, leaky injectors, fuel pressure regulators, spark plugs. Also car has no road tax or insurance so limited ability to do any meaningful road testing. Maybe continue with known fault as engine being pulled apart anyway?

[Paul Woods]

It's basically anything and everything that could be causing it, but the bottom line is too much fuel or unburnt fuel.

Quick insight, the long term fuel trims drive the short term trims as close as possible to zero, if you had zero long term your short term would be -25. So the long term gives a base adjustment to give the short term a better range. Now the short term drives the AFR sensors, keeping them hovering around lambda 1 or stoich. If the AFR goes weak the short term adds fuel to drive the AFR to rich, then subtracts fuel to drive the AFR weak....and so on and so on.

For the long term to be so high/low means it is struggling to keep the short term around zero, if the fault gets worse the long term will max out, quickly followed by the short term also maxing out with a large negative number, and the AFR will flatline at its richest reading unable to be driven to stoich.

Ok so lesson over, rich running can be literally anything, start with a basic compression test on all six cylinders, now there are clues helping you here, it would need to have low compression on at least one cylinder on EACH bank, remember your long terms are pegged to -25 on both banks, so each fuel system is experiencing the same issue, so it's a blanket fuelling problem.

You can pretty much rule out a compression issue but check anyway. Also check cambelt timing. After that I would suspect the MAF, as it is one of the few things that affects both banks. Also possible is regulator, but they are in tank on the rx300 and never go wrong.

Reset the ECU by taking a battery terminal off for a few minutes, restart the engine and note the fuel trims again and that both banks are in closed loop.

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[rainen]

Thanks. Done the battery off and both go into closed loop. Long term goes back to similar negative readings. Not sure how you get a compression tester onto bank1, but guess its plenum off. Might have a go at cleaning the MAF first.

[Paul Woods]

Yes try cleaning the MAF but it's more likely to be faulty. Also induce an air leak at the throttle body by removing a vacuum pipe, the short term for both banks should immediately go slightly positive value and sometime after that the long term will reduce its negative value. That will at least check the system is working as it should be.

You can also buy a MAF for a mk3 mr2 if you want to directly try something, it's the same as the rx300 MAF.

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[rainen]

So cleaned the MAF and reset the ECU which has given a different set of results. The short term is hovering between -12 and -14 on both banks and the long term settled at -18 on both banks. A better result than last time although still not right. Did take a vacuum off the intake and yes the short climbed straight into a large + number. Did not follow through with the long term (probably cover that off again tomorrow while the engine is warming up for the compression test). The engine is very slow to respond to the accelerator pedal and takes about 1-2 seconds before it picks up. Given the results are better after cleaning the MAF guess a new one would be the next option to try. Hoping to do a compression test on cylinders 2,4,6 tomorrow as they are easy to get at. Will post up results of compression and new MAF when I get it on to see if we can get a good set of running data before I start to take the engine out of the car and pull it apart.

[Paul Woods]

Those results aren't better, that's actually a worse result than last time, originally you had zero for the short term and -25 for the long term, adding your trims together giving you a total of -25% fuel being subtracted by the ECU.

This time you have -12/14 on the short term and -18 long term, giving you a combined -30/-32%, if you let the engine run long enough the long term will peg at -31.5% (it absorbs the -12/-14) and the short term will just about be zero, which will keep the AFRs at lambda 1.

The system is trying to remove fuel to compensate for what it is being told by the sensors, now it would have to mean both AFR sensors were faulty to make both fuel system banks behave the same way, unlikely, so I do think it could be the MAF.

Whatever is causing it is affecting both banks universally and the MAF would do that.

Presumably there is nothing odd looking with the air intake before or after the MAF and the air filter element is present? These MAFs are super sensitive to even the slightest change in air flow, I'm talking a butterfly wing beat ahead of the MAF will upset it.