VVT Bottom-End Rebuild / Refresh
 

Hey guys - first 'serious' post in the engine category on the forum - I typically post over in the 'build-threads' section (link in sig) – so be kind ;)

This is also my first crack at rebuilding / upgrade engine internals. I've done most other things, but never internals.

As such, there has been / will be LOTS of continuing research as I go along – input welcome


The Symptoms:

-LONG cranking starts
-Horrible exhaust smell
-Horrible gas mileage (5-7 mpg average)
-VERY lackluster power (close to a stock Miata)

I’ve determined that I have been washing the cylinder walls with fuel - my dip stick smells more strongly of fuel than my gas cap does! Haven't completed a leak down / compression test yet – (forthcoming) - but this seems to be a fairly straight forward - I'm at peace with it.


Car Parts / Intended use:

Car daily runs 60-70 miles @ 7600ft elevation (primarily commutes, not track) (Installed parts are in my sig)


The Project:

-Leave VVT head as-is (remove / clean)
-Re-use previously-installed forged rods (assuming no damage)
-Re-use stock cast pistons/ wrist pins (ditto)
-Re-use stock crank (ditto)
-Verify / resurface head/block if required (never overheated – but new gaskets are picky?)
-Send block out for bath and measurements
-Minimum re-hone cylinders - possibly over-bore slightly if req’d (0.5mm / 1mm)
-Install new ARP Main studs (I know I have head studs, not sure of others)
-Install new ARP2000 rod bolts
-Install new ACL race bearings (Main / Rod / Thrust)
-Install new rings (NRG, CP, JE, Wiseco, Mahle, Manley) – (matched to larger bore if required)
-Install full OEM seal kit / Timing Belt / WP / Clutch master & slave / motor mounts, etc
-Billet (race) Oil Pump (Boundary Engineering) – (skip the crank damper)
-Other?


THEN:

-Break in the engine using stock hardware only, disconnect Link & extra injectors


THEN pt. 2:

-Replace modified intake manifold (4 additional injectors) with stock NB2 intake manifold
-Install 650cc injectors (ID 1000cc instead? – No ethanol)
-Install Megasquirt (considering MS2)
-Verify Walbro 190 fuel pump, if not - upgrade
-Tune / get it running!


Questions:

-What else have I not considered / included in my 'To-Do' list?

-Any reason to tear into the intake manifold due to damage (not looking to upgrade)

-Compression. I’d prefer to run my OEM cast pistons – but there’s a possibility of required over-boring the cylinders due to scoring / damage… so I’m assuming my stockers won’t work if over-bored, correct? (In that case, planning to go with the 8:6:1 units)



Work begins soon. Parts are already in the cart – ready to be shipped.

i would first do a compression check.

change oil to flush out the gasoline soaked oil.

Then figure out why you are running pig rich.

your engine might be fine, and you are just drowning it in gas.

In some ways, this thread / plan of action may be a bit early - there ARE obviously some basics to get out of the way first. Agreed - compression/leak down tests are planned, and an oil change will be required, regardless - I'm hoping that fresh oil *might* help re-set my situation.


Would 'cylinder washing' actually cause this big of a power loss and such poor MPG's? I fear the rings are toast for the symptoms to have gotten this bad.

This is where I've been puzzled. On one hand I have good AFRs, but horrible mileage and power (suggesting over-fueling and cylinder wall washing) - so I assume that if the oil change helps me 'rest', my AFRs will be INSANE and require a complete reset, tuning table wise.


Fingers crossed. Oil change tonight, comp check when the tool gets in

you can borrow a compression checker at any autoparts store for free.

was this same tune running reliably before? when did this crazy richness start?

Agreed about the tester - got one in the mail, here tonight or tomorrow.

Honestly, I don't have a lot of history with the car beforehand. The PO did have a very good history with the parts/tune (he is a very trustworthy source). Car has been on the road... idk, 10hrs since all this work - I did have to bump the fuel maps up when getting the car running (this old Link stuff is kinda annoying / vague).

After the oil change tonight I'll do a full tune-reset (I have FM's recommended values) and go from there.

No wideband?

Wideband installed and functioning well.

I *thought* things were doing well (while they weren't) - I did bump up fueling at one point (can't remember exact order of things) to help with idle / AFR values.

I was idling between 14.5/15.0, 11.0ish at full boost (12lbs), 16.0ish at cruise (Link doesn't kick in the extra injectors w/o boost). But at the same time I've been getting horrible gas mileage, horrible exhaust smell and massively down on power (can't maintain 75mph in 6th, have to downshift to 5th @ 4200rpm just to hold 75!)

Like I mentioned above - after doing an oil change tonight I'll also do a full Link reset - returning to FM recommended values. Megasquirt is in my future, regardless.

You have to go with a MS3 to work with VVT. I would not fuck around with a MS2 and then have to install a VVT Tuner.

Thank you for the input.

I had considered the MS2 for cost-sake - I do not want to have to install a VVT tuner.

MS3 it is

May not be a bad idea to post your timing table... you mention it's running rich, but at 70mph cruise you should still be near stoich. A bad tune would definitely cause lack of power and terrible gas mileage.
On the other hand, I know nothing about how a link works, and dual injectors seems utterly ridiculous for a GT2560 :)

Edit: I just looked at the Link manual. You seriously tune this thing with a 1x48 character display and a couple buttons? O.O Burn it with fire, get a megasquirt.

Good god, 5mpg? Are you experiencing misfires? Curious if you are fouling plugs? I'd wanna double check that wideband sensor somehow if you're using that much fuel and still getting normal AFR readings. Did this creep in or was there a sudden change at some point?

Yes, exactly... this thing is... mystifying AND a bit frustrating. I have the recommended FM values and will reset the ECU to those with an oil change this evening. Kinda a mess - would like to get away from the Link and into Megasquirt asap - but that also brings a steep learning curve! It'll be worth it.


Agreed, I've been averaging between 5-7mpg. I've got a 30 mile trip (one way) to work - in that distance I clear roughly half a tank (premium) - not great.

I haven't had any miss-fires (that I have noticed / heard) - a quick check of the Engine Light (will be on forever - check my Kart build) will verify. I understand the CEL usually 'blinks' when a miss-fire is detected? The wideband sensor is brand new, and controller is a nice unit (Autometer Wideband Pro, 5778 Phantom Series). When installing I did look through the manual trying to find anything about open air calibration - didn't see anything noted.

Popping the plugs for a quick look while completing my oil change and checking timing tonight will tell if I'm fouling the plugs! Will update.


The issue has been ever-present (since start-up) - this turbo setup was in a different car that ran dependably before I swapped roller-skates. (Here: https://www.miataturbo.net/build-thr...3/)

I ran the setup on stock settings, but was getting AFR readings near 15.0/16.0 (16.0 is the limit of this wideband?) on boost - so I adjusted up the 'master fuel adjustment' setting off '10' (FM recommended) to around 20, which currently gives me 'good' AFRs. This Link has me pulling my hair out.

Update:

Good News: Completed an oil change last night - have a magnetic plug, didn't notice any metal shavings

Bad News: Ran a compression check after the oil change - on the second try (with teaspoon of oil dropped in) these were my numbers:

1. 105
2. 143
3. 113
3. 113

When I pulled the plugs, these are what the looked like (1,2,3,4):

Attachment 227998
https://cimg4.ibsrv.net/gimg/www.mia...73ab891d03.jpg

So - next steps:

Engine removal / tear down - block inspection - then determine whether or not I can simply do a honing / ring job OR see if I have to do a slight over-bore w/ new appropriately sized pistons/rings.

Oil pump, bearings, head studs, seal kit (etc) are all assumed.

Looks like 1 & 4 weren’t even firing. Maybe check that coil. Did your used oil reek of gasoline?

1 & 4 do indeed look VERY clean - kinda odd - these plugs have... maybe 500-750 miles on them.

Yup - as mentioned above, I was concerned that the engine was getting cylinder-washing - the oil and dipstick did smell like gas. Compression check was with new oil and a warmed up engine.

I was considering checking timing, but at this point that doesn't matter - those compression results are pretty clear.

isnt your engine shaking like mad with only 2 cylinders firing?

im surprised you even drove the car in this condition.

you can check spark on cyl 1&4 with a timing light clamped to the ignition wire for cyl 1&4

did you recently do a timing belt change? could timing on the belt be way off?

I think it would be good to know if you're not getting spark, and have that fixed before the engine goes back in.

No timing belt change. Car doesn't have the many miles on it since the 're-assembly' - and honestly it didn't shake much, it wasn't silky smooth, but wasn't bad. I've got a light and will give spark a look.


Agreed.

Yea based on those plugs, the atrocious mpg, and fuel smell(unburned fuel in cyl 1/4 just leaks past the rings) in the oil, I'd say its a safe bet that the coil bad on 1/4. Since it is completely not firing on either it might not make a huge vibration as the firing pattern may not generate any abnormal as the two firing cylinder are 180 apart vs say it running on 3 cyl with one being 90 out but sure you would have noticed a SERIOUS lack of power when driving with only having 2 cylinder

As for the compression numbers I assume you ran the test at WOT otherwise the 3 dont look bad it it was closed throttle but Id want to know the before and after the oil in cyl to make a judgement.