I'm back again with another quite confusing problem with the 00 EX coupe with the d16y8 5 speed swap! Here's the rundown this time: Strange intermittent misfiring and gappy acceleration.

Symptoms: I was driving home one night and she was running smooth as butter. Me and the misses decide go somewhere to drive-through for food and the engine starts idling terribly in the line and sounding like its missing every now and then. It isn't a steady misfire that happens every revolution but instead it's one that comes and goes out of the blue. The idle will be smooth and normal and then it will randomly hiccup or putter every few seconds. Also, if I try to leave out in a hurry with wide throttle it just gaps out big time on me and barely goes now. NO check engine lights or oil/battery lights either. There is no idle bounce or hunting that would be associated with IACV problems and I've checked all my vacuum hoses, even replaced a few of them that looked old and flopped out/collapsing. Only the pesky idle that seems low and burpy and the gapped out throttle are present. If I open the butterfly SLOWLY with the pedal it will raise the RPMs smooth up to redline the way it used to, but if I go from closed position straight to wide open throttle or anywhere else up there it gaps out and seems like it has trouble catching up to what I just tried to do. The idle eventually catches up to the input I'm giving it but it's slow to get there and very gappy or "bogged" on the way. It's the same way when I try to drive it. If i let off the clutch easy and barely give it any throttle the whole time you wouldn't know there was anything wrong with the car but when I try to stomp the thing wide open or go fast at all it just putt-putts and doesn't deliver. It misses so bad under wide throttle that it's tough to get around town and maintain 50mph but it can idle and drive around the block slowly all day long. It doesn't die or have trouble starting at all. When I do a cold start after a night of letting it sit I can do wide throttle with no problem but once it warms up to operating temp the symptoms come right back. I took a video of the slow throttle raise compared to the quick throttle raise and the gappy-ness I'm referring to. I'll be posting this later on.

Things I've tried so far:
-Compression tested at operating temp. ~160/170 range on all four with little variation. Holds compression for as long as you're connected.

-Checked timing, cam and crank lined up but I re-did the timing again anyways for the hell of it.

-Checked valve spacing and cam rockers. The lash needed a tiny bit of adjusting but everything looks normal and with a few spins of the cam I watched all the rockers go up and down as they're supposed to. I figure a stuck/ruined valve would cause a regular and constant misfire on every revolution but this one I have seems to only be intermittent.

-Got rid of some already new NGK plugs and replaced all 4 with identicals just to be sure and verified the new gaps. The man said the old ones looked as if the car was running rich so whatever - I got some new ones just to be sure.

-Pulled injectors and fuel rail all together and cranked the engine so they could spray into a big fat towel. All 4 seemed to spray well and spray even. This was just a visual test after all though. Haven't checked exact fuel pressure yet but when I undo the banjo it seems like it has a fair amount of pressure in there. If the car is idling and I undo the injector clips one at a time they all show a decreased idle and then when I plug them back in it returns to normal. Same deal when I remove the spark plug wires one by one. I first started doing this to attempt to single out a specific cylinder having a problem. They all seem fine.

-Back probed old TPS and it looked good on the meter, but I swapped it out with a known working one just to be sure and didn't change anything. Both were calibrated to exact specs before test runs.

-Checked dizzy cap and rotor. They looked a little old and friction worn to be honest so I replaced them with some crap brand ones just to help the process of elimination along. I didn't note any difference here either.

-Oil and coolant are not mixing and I don't have any exhaust fumes or bubbles in the radiator/reservoir. Oil is blacker than sin but still has a decent smell and feel to it. Coolant is still green and smells like coolant.

So I have confirmed compressed air, fuel, and spark. Ughhh. What am I missing you guys? I have been considering EVERYTHING, including the possibility that I might have purchased some bad, old, or tainted fuel from one of the local stores. I usually run no-ethanol but getting low on the other end of town forced me to buy some regular gas lately. I hope I didn't goof and buy some watered down crap.

Another thing I've started doing is pulling plugs while the car is doing its poor idle act to see what kind of reaction I can get. I've noticed that unplugging the TPS while it's running doesn't change the idle or driving conditions at all. Some threads I've read claimed that unplugging the TPS would temporarily fix their problems via the ECU re adjusting the fuel. It didn't fix mine but it threw the CEL for the missing connector, which is usual. I reset the ECU and went back to it. Unplugging the MAP sensor on the other hand totally killed the car and I had to re crank it.

The next thing I tried unplugging was the CTS or what some people call the Engine Coolant Temperature Sensor. When I unplug THIS particular connector from the plug on the head it raises the idle a bit above 1 and stops the sputtering altogether, even at operating temp. It smooths everything right out. This does indeed throw the CEL for the missing connector but it smooths the idle. The wide open throttle problem is still present when I try to leave though. Is this indicative of a fuel output problem? I've heard that a faulty CTS will make the ECU think the engine is either far too cold or far too hot and as a result make your car run rich or lean. I've also heard that a stuck or damaged thermostat would do the same thing.

I know I'm kind of throwing parts at it by this point but a lot of them were old and needed to be replaced anyways. If I was to buy more it would probably be a replacement CTS and thermostat. Would I just be wasting my time? Any suggestions are appreciated!

 

It's refreshing to see someone who has actually done some proper, logical troubleshooting before creating a thread.

Know someone with an identical ECU you could swap in to verify it is working correctly?

 

I don't know anyone else with a 5 speed coupe. I still have the ECU from the automatic engine but I think that would present a whole host of other problems if I tried to hook it up, right? These problems just came on out of nowhere like a switch. It was taking me back and forth to work (quickly) with no problems the day before... Its like something just suddenly failed or came loose somehow.

 

well, you will get unrelated CELs...I'm worried about the IACV if you do it though. I could be wrong, but I think the auto Y8 uses a 3-wire while the manual version uses a 2-wire.

Perhaps someone else can chime in and confirm my suspicion.

 

Yeah that's one of the things I had to change for the swap. I had to get a new intake manifold to match the 2 wire IACV and then I had to change the plug on the harness and repin a couple things. The old automatic IACV on the throttle body is blocked off with a plate I made and bolted up tight.

 

Hmm, are you sure that plate is as tight as you think...?

 

I could check to see if its leaking. I made sure to use a rubber gasket and all the original bolts for the plate but it's worth a look.

 

No luck there. Everything's the same.

Any other idea what it could be?

 

Dead thread!

 

If its running rich than you might wanna look at the o2 sensor.

 

I'll give that a look too.

 

O2 is still in the exhaust and is plugged in and functioning. No CEL for that either.

Anyone have any other ideas of things to check?

 

All things being equal, I'm still leaning towards timing. From what I read you only verified mechanical timing. I didn't see where you checked ignition timing with a timing light.

 

I've never used a timing light. How do you use it? I'm assuming you're referring to the distributor?

As I've mentioned before, this car was running top-notch for a few months and this problem came on out of the blue one night... Is it common for ignition timing issues like the one you're describing to come on suddenly like this?

 

I thought I had all the problems licked when I rebuilt it this time around. It ran great and strong for a few months too. The head is newly resurfaced and the valves and valve seals were all checked by the shop and again visually checked by me when I reinstalled the cam and did the rocker spacing. The surface had a bit of warpage before I took it to them but they did their tests on the head and said it was good to go after the repairs. New headgasket from the Honda dealership was used as well. Torqued the headbolts in steps to the proper specs with a brand new torque wrench. When I started having this misfire problem I checked and rechecked to make sure none of them backed out. They're still snug as could be and I still have good compression. I am fairly convinced that my head is firmly set and sealed to the block surface this time. That was my problem before and I think I've moved past that with this rebuild. It was running like a dream after I put it all back together until some imaginary switch flipped over in the drive through and it started missing on me. How could it be going so good and then just poop on me like that out of nowhere?

My friend is convinced that it's a problem with my valves or something else on the top end. I don't see any broken springs or any warped rockers or anything else that would cause a combustion problem down below. This has me completely stumped.

I tried some new gas with NO ethanol today because the car has almost run empty from me toying with it in the driveway over time. Has anyone heard anything about using HEET in a Honda of this vintage? I've heard that poor quality fuel or moisture in the tank would cause the type of problem I'm having but I'm always hesitant to add "Lucas" or any other kind of additive to my engine or fuel system.

 

I did a bit of digging and figured out how to use a timing light. I'll do that the next time I'm fooling with it and post the results. I'm also going to check for vacuum leaks AGAIN. Ughhh maybe I missed something?

 

This thread is deader than dead again. This may be the last time I come to honda-tech for help. I'm more likely to find out on my own at this pace. It's either that or everyone who reads my thread is equally as stumped as I am. I appreciate those who have thrown in their two cents but I usually get more replies than this. Has this forum lost a lot of members or something?

Does ANYONE have any other idea what could be causing the random misfire? I'm checking and re-checking everything on the engine. In the midst of my troubleshooting I had a code come up for P1337 Crank Speed Fluctuation No Signal... I quickly located the source of that though. It turned out that my alternator belt had eaten clean through the wire going to the crank sensor. I did a little doctoring to the wire and now I'm back to absolutely NO check engine lights but still misfiring and bogging out like crazy when I try to accelerate. C'mon. You guys have come through and saved the day before! If I figure it out on my own I'll be sure to post the results.

 

I know it’s been a while but did you ever find out what the problem was?