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Rebuilt engine, running crappy need help

4K views 20 replies 6 participants last post by  mitchellallan26 
#1 ·
I rebuilt the engine in my 2003 6S, timing is all correct, tensioners are good and tight, new spark plugs and coils, piston rings and bearings, gaskets, etc.

It runs like it has a constant misfire, but no codes related to misfires. Only code is a pending P1410, because someone got rid of the stock airbox and put in a CAI. I can't even look at the fuel trims because the fuel system keeps switching between Closed Loop and Open Loop - Fault. Could that be an O2 sensor problem?

Anyway, I've been on this path of assuming my cats are clogged because the previous owner said it burned alot of oil. The front precat is new, and so far I've removed both main cats and welded in straight pipe, just to see if it would run better. It runs better than when I first started it, but still crappy. I'm going to do a leakdown test before I remove the rear firewall side precat, but it's like I'm tracking down ghosts.

Also another weird thing, it runs better above 2.5-3k rpms, but when I rev it that high it takes a few seconds for it to come back down. Almost like I'm still hitting the throttle but I'm not. Throttle body problem? Or related to the fuel issues?

I'm starting to regret buying this Mazda..
 
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#3 ·
That's crazy. I'm never buying a Mazda again unless it a brand new one because those aren't made by Ford anymore. I've seen Toyota engines that were shot, insides all sludged up, chewed up bearings, and overheating that would still run fine. This Mazda engine was clean as a whistle on the inside, has all new parts and still runs like a turd.
 
#4 ·
Between running rough and running better about 2500 or so, I'd wonder about vacuum leak/leaks. Depending on brand of CAI, check if the factory accordion tube has cracks and splits. Upper to lower intake seals can start to leak for no reason. (i'd try snugging them before replacing)
 
#10 ·
So I reinstalled the gutted rear precat and hooked everything back up. At this point there is only the front precat intact, which is new.

Runs worse now... when I hit the throttle it's practically unresponsive. Idle is just all over the place, like it's constantly missing. I checked my front spark plugs and they were black-ish (also brand new), probably from the misfiring. No misfire codes yet though.
 
#11 ·
This right here is my fear, that when I finally get this MF-ing car back together with some form of a Fusion engine, it's going to run like crap or something.

All electrical connections in order? I'd probably let it run longer and see what codes pop up.

Maybe take off your front O2 sensor and have a peek down in the front precat, just to make sure it's truly clear. Even if it was replaced, I suppose it could re-clog with oil burning in a relatively short period (so I've heard).

Mine looked awesome when I removed the O2 sensor. Yay, emissions.



Sounded even better when I got the manifold off and shook it. This was before I did anything to attempt to gut it.

Video of front precat shake-out
 
#12 ·
Wow yours is really clogged, mine actually didn't look that bad. Only the front main cat (the one that goes past the oil pan) was really clogged.

Today I did a leakdown test to rule out leaking valves or rings (even though the rings are new and I lapped all the valves). My leakiest cylinder showed only 2% leakage, which is outstanding. For anyone who doesn't know, leakdown test is like a compression test but more accurate. Anything under 10% leakage is good, 10-15% is just OK, anything over 15-20% is looking like a rebuild/blown head gaskets, etc. SO not my problem there.

Let it cool down and started it again, hooked up my scanner just to see what the sensors are saying. Bank 1 (which I believe is the firewall side) O2 sensors looked fine and the fuel trims were 0%. Bank 2 O2 sensors sat at 0.02 volts and wouldn't move. It supposed to oscillate between 0-1 volts but this one wasn't. On top of that, Bank 2 short term fuel trim was -20%, meaning it was pulling fuel instead of adding it (like it would in a vacuum leak). So my next step is to replace the front upstream O2 sensor and see what happens.
 
#13 ·
Yeah, mine was destroyed. My rear one looked ok from the bottom, but I gutted it regardless. Of course all the cat gutting did nothing to help my engine that was burning insane amounts of oil, hence the ongoing project to replace the engine. Probably should have just rebuilt mine a month ago...

Odd about your O2 signals. I guess start by making sure all connections are totally intact, then replace sensors. Good luck man. Nothing worse than a project lingering on well past when it should have been completed.
 
#15 ·
Its too bad the engine is such a piece of shit on these, because I really like my car.
This. I've owned this car for a few months, have driven it all of 1 mile (testing after rebuild) and I hate this engine.

My lack of fuel to the rear bank continues. Since my last post I've checked fuel pressure, replaced the rear upstream O2 sensor, gutted my rear cat (not sure if I already posted that), removed my EGR valve, and replaced all 6 injectors. Fuel pressure was 70psi at idle, no problems there, now both upstream O2 sensors are new, injectors are new, upper and lower intake seals are new, pcv valve is new, there are no cats besides the front precat which is new. The EGR valve was sticking I'm pretty sure, it ran better after I removed it and blocked off the hole but still the same fuel issues.

The live data from my scanner reveals that Bank 1 (firewall side/rear) fuel system stays at Open Loop - Fault status, which is why it won't correct fuel trims and continues to run super lean. Upstream O2 voltage is like 0 - 0.015 volts, basically its seeing no fuel. The front bank is fine, switches into Closed Loop and starts correcting fuel trims. Sometimes while revving it the rear bank will switch into CL for a few seconds and actually dump some fuel in, but then it will randomly switch back to OL-Fault. Running out of ideas here..
 
#16 ·
Jeez man. Sounds like some sort of a wiring issue at this point? Clearly you've replaced everything possible.

Don't hate the engine too much, hate the emissions garbage that made it grenade in the first place. Some days I can't believe that our MPV is still kicking ass at 196k. Leaks a very tiny amount of oil from the timing cover and one of the exhaust manifolds must have a tiny leak or crack, but it seals up once it warms. Engine is smooth, quiet and (relatively) powerful. Amazingly, being a 2004 like my 6 wagons, it seems to have none of the emissions issues. Well, it has given us a precat efficiency code since day 1 (bought in 2012 w 126k miles) but has never affected how it drives. I probably should make the time some day to peek inside those precats and consider gutting them too. Who knows, even with them not destroying the engine like a 6 does, they could be partially clogged and hurting performance.
 
#17 ·
Just got a call from the ECM Repair place, they couldn't find anything wrong with mine, said it tested fine.

So now I'm at a loss. SOMETHING is causing me to have Open Loop Fault mode and not letting my stupid rear injectors fire. I wish I could somehow tune this thing or bypass it.
 
#18 ·
Dude. Sorry to hear it. I'm sure you're about ready to junk the whole thing. I know I'm close w both of mine, but at least I know they don't run because I have them in 1000 pieces.

I wish you strength and patience. I'm sure you are running low on both.
 
#19 ·
Sad to say, but I'm giving up and selling the car as-is. Hoping to get $2k for it but we'll see. It doesn't run bad, just bogs down in gear.

As a recap to the work that was done and new parts:

-Rebuilt engine with new rings bearings (compression 175 psi / leakdown 2% across all cylinders)
-New water pump/thermostat
-New platinum spark plugs
-New coil packs
-New Denso injectors
-New head gaskets/intake gaskets upper/lower, exhaust gaskets, valve stem seals, etc.
-Valves cleaned, polished and lapped into heads
-New upstream O2 sensors
-All cats removed thinking they were clogged (both main cats were clogged)
-ECU tested by SIA Electronics, couldn't find anything wrong
-Throttle body and EGR valve cleaned
-New PCV valve and silicone vacuum hoses

Recap of problems:

-Sounds/feels like a bad misfire, surging, heavy bogging in any gear, rough idle, etc.
-Only error code is P1410, which is apparently only a pending code because it has a Cold Air Intake
-Engine struggles to go into Closed Loop fuel system, mostly sits in Open Loop-Fault mode and won't adjust fuel trims
-When it does manage to get into Closed Loop, front bank subtracts fuel and rear bank adds fuel by the same amount (i.e. -25% front, +25% rear) and it smooths out
-No vacuum leaks detected at all, idles OK sometimes and can rev all the way through 4-5k in neutral just not in gear


But I'm tired of spending time/money on this, so I'm trying to sell as-is. It's a shame because its such a clean car. And it's the grand touring edition so it has all the bells and whistles, Bose sound system with factory sub/amp, tint, side skirts, heated mirrors, heated seats, leather interior and power seats, sunroof, etc. Oh well, that's what I get for buying a Ford.
 
#21 ·
If you haven't sold it by now

As dumb as it sounds if you still have the car check in fuse box in engine compartment, check your ENG BAR, ENG BB, ETC, IG 1, and ENG+B fuses. My car ran like crap the same way, clogged up the cat and blew the motor, after an engine swap, gutted cat and new clutch, just because I was in there, it still ran like shit, I found a blown fuse I think mine was the ETC but not positive on that, I replaced the fuse and my car was fixed, idle didn't jump around, car stopped stalling, and had no lagging in power when taking off. Hope this helps let me know What happens.
 
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