OK, this is a long dissertation, but please read and help a guy out...

I had a small off-idle stumble on a D16 ZC SOHC Vtec. I saw that the throttle body was packed with carbon and trash from sitting on a fish dock somewhere in Japan.

OK, after cleaning it, I got a terrible bogging at the slightest throttle.

I have an identical engine in a civic, so after testing each sensor individually, I decided to start swapping to find the problem. Again, I am not an idiot. I tested each sensor with a multimeter. I also have no CEL codes.

Here is a list of items I have switched out from a known good engine, and even more importantly put the sensors into that engine and it runs fine!:

Manifold Absolute Pressure sensor.
Throttle position Sensor
Intake air control valve
Fast idle thermo valve
Intake air temperature sensor.

Throttle body.

Intake gasket (Three times)

Distributor

O2 sensor

ECU (Running a P28 from an auto, converted to manual) but I also switched it with one from a manual.

Injectors (Switched from resisted to non-resisted type)

PCV valve.

PLUS, I disconnected and plugged each hose that goes into the intake one by one with no change.

Oh, I even changed out the intake itself with a USDM intake and went back to the JDM one after I had it vatted!

Spark plugs.

Fuel filter.

I have even checked the timing each step of the way. I have been at this for like a freaking month and a half now!
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OK, so all along this acted like a vacuum leak somewhere. The engine idles nicely and will sit there and purr all day long. It does smell a little rich (Which also leads one to believe that there is a vacuum leak) But as soon as you try to move the throttle it starts to bog. If you can get it past that point, it again bogs at around 3000 RPM and with a load (Clutch engaged) it dies every attempt to move the car.

I am telling you, this is the oddest thing I HAVE EVER encountered. Everything points to an air/fuel problem, but the fuel system seems fine, thus leaving air. I wish I had a wide band sensor to check the AF, however I dont.

Again, every single piece of one engine runs fine in the other. That is, again what makes me think there is a vacuum leak somewhere that I cannot find. But, when it is idling, you can put your hand over the throttle body, and the engine dies immediately, just like it should!


So, anyone got any ideas? This is driving me crazy!

 

It seems like it should be an electrical problem.

From what you have said the sensors seem fine, but all sensors relay via wires, it could be some wiring somewhere is stripped.

 

sounds like u got a problem

 

To find your a vacuum leak, put your palm over the throttlebody opening while it is running it should stall.


Did you reset your ECU after the cleaning?

Spark plug wires good? Does the problem get worse when it is raining?

Return line pinched?

 

Did you swap the FPR yet?

 

fuel pressure or spark issue? (timing not advancing) I would try removing each vacuum line that goes to something important (vacuum fuel advance, map sensor, ect) and testing it for blockage.

 

OK, just a little update:

I replaced the FPR with a known good one and I still have the same problem. The old one is now on my other running engine and working fine.

So, on my (Good) running engine, these parts from the (Bad) running engine are working fine:

MAP
IACV
FITV
IATS
FRP
Dizzy
P28 ECU
Injectors
Intake
Throttle body
O2 Sensor
Every stinking hose!

I have checked all grounds and checked continuity of all electrical wires.

I am really stumped! The damned engine fires right up, and idles great. But the second that the throttle pate begins to open, the engine bogs down and stalls. It smells way too rich as well.

I am going to buy a fuel pressure guage to check my fuel pump. But the question I naturally have is, "If the fuel pump is bad, how could it be running too rich?" Wouldnt it run too lean?

Give me some more ideas, guys! I want to finish this damned CRX for my kid so I can strip out the Civic and re-paint it this fall.

One more thing, I completely removed the EVAP system as well (Just like I did on the Civic.) All the vacuum lines are blocked off, and the purge solenoid has been removed.

Just kicking this out there as an idea... Could the timing have jumped a tooth? I am able to time the car fine (Set at 12-14 degrees) but if it were off a tooth, when the computer tries to advance the timing, could this cause the stalling? I suppose it could. What do you think?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JohnnieChimpo &raquo;</TD></TR><TR><TD CLASS="quote">Did you reset your ECU after the cleaning?
</TD></TR></TABLE>

 

If the cam is off a tooth it will be hard to set timing. Loosen the valve cover, pull the top timing cover off, use a 17mm wrench to turn the engine (or put it in 1st and roll the car while watching) and make sure the cam is in time. It should say UP on the cam pulley and the TDC mark is like 2" behind the ignition timing marks.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by salman &raquo;</TD></TR><TR><TD CLASS="quote">Did you reset your ECU after the cleaning?</TD></TR></TABLE>

Yeah, I sure did. Every time I made a change, I reset it.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DPSJosh &raquo;</TD></TR><TR><TD CLASS="quote">If the cam is off a tooth it will be hard to set timing. Loosen the valve cover, pull the top timing cover off, use a 17mm wrench to turn the engine (or put it in 1st and roll the car while watching) and make sure the cam is in time. It should say UP on the cam pulley and the TDC mark is like 2" behind the ignition timing marks.</TD></TR></TABLE>

That was what I was thinking. And again, it idles nicely. I think I have it set at 14 degrees @ 700 RPM at running temp. And yes, I jumped the service connector (Well, actually I got tired of doing that, so I wired in a switch LOL) and ran the temp up until the fans turned on before setting the timing, just like the service manual says to do.

I will check the timing belt tomorrow if I get time and make sure the cam/crank gears are properly aligned, and the tensioner is set correctly. But I believe it is already, why else would it be so easy to set timing?

Does anyone know of any good tricks to finding pesky vacuum leaks? I usually use a can of carb cleaner and spray around until I get an idle change. Naturally, I did this, and could not get the idle to change, but it is extremely difficult to get the spray on the bottom of the intake manifold.

The last time I changed the intake, I used one of those thick assed Felpro gaskets, hoping that the mating surfaces were just a little off. This **** is really bugging me, and the car is un-drivable.

 

what about the TB gasket? It didn't seem like you mentioned that.

 

check the brake booster 1-way valve for leakage.

also try another thottle cable. Could be hung up inside?

 

it sounds like a vacuum leak or your timing is off.