RobocracyAlpha

This issue ended up being the upstream o2 sensor. It passed all multimeter testing and diagnostics. However, it was unresponsive at a very specific temperature range.



So, i have a 1997 Honda Del sol SI. Currently running a d16y8 and MANUAL tranny.

I purchased the car for nearly no money because someone had started an auto>manual swap...but didn't finish. They had simply swapped the tranny and quit.

The car was driveable upon purchase but was still running an auto intake manifold/iacv and an auto computer.

One week ago i swapped the manifold and ecu with direct OEM matches for the manual version of the car.

Now it idles correctly(kinda), and fuel/air has drastically improved.....
However, now when the engine is warmed up, and under load, the car stumbles(almost like a misfire) at around 3100 rpms in any gear. Especially when i am geared a little too high and the engine is under a heavier load.

I can "power" through it by slamming the accelerator or jumping down a gear.

Here are the things that i have replaced to try and fix the stumble:

New Map sensor
New timing belt/water pump(100% in mechanical time as of today)
new TPS
new fuel injectors
new fuel rail
cleaned IACV
checked and adjusted ignition timing
new spark plugs/wires


UPDATE:
New coolant temp sensor
New fuel filter
NOW popping ecu codes: P0171 and P0170(pending)

I am now stumped. I initially suspected fuel supply..but that doesn't seem to be it because i have replaced injectors/rail

Also, the idle roams slightly(idles up for a second, then idles down for a minute, then idles up for 10 seconds, then idles down for 3 minutes.... and on and on.)
and occasionally when im turning into a parking lot and quickly disengage the clutch...the car acts like it wants to die. However it has never completely stalled out.

Any help would be greatly appreciated.

JarvisW

I have practically the same problem. It bogs at about 3500 or so, but mine is manual. I just learned to go around the spot in rpms, either lower or higher depending on needs.

But I've cleaned FITV/IACV and checked timing, and did tune up etc.

I think its the IACV, but I can't be sure and its too expensive to just throw money at.

FSM pretty much says that too.

BUT, it might also be air in the coolant, tho, its done this through 2 coolant changes and half a doz burps too

RobocracyAlpha

I have thought about air in the coolant lines. I'll give it a look tomorrow. THese IACV's rarely go bad...they are usually just dirty. And i cleaned the living **** out of mine. I'll let you know what i find out after i am 100% sure there is no more air in the coolant lines.

RobocracyAlpha

Any other ideas? Anyone?

delsolintegra

In my 93 del sol si I had a lot of the same problems you are having. I changed a lot of things but what finally solved the problem was replacing the coolant temp sensor. It was sending the wrong signal to the ECU and the fuel ratios and timing were off. I never got a cel light for this condition.

Also if you have a cold air intake filter make sure it is not pushed too far on to the intake tube that it causes an internal restriction to air flow.

RobocracyAlpha

nice man, thanks. i have a coolant temp sensor(new one), that i was considering putting on. But i didnt know id that would help anything. .

RobocracyAlpha

I put in a new coolant temp sensor and new ram air filter just to check those off the list.

Still no improvement.

Ohmega

iTrader: (1)

Could it be the fuel filter needs changing? Just a thought.

White_EG1

When you cleaned out the FITV did you spin the plunger all the way back down?

There's a possibility, if OP went longer than 15-20k miles on his current.


OP, you should have did a full tune up first, and not just thrown parts. MAP or TPS, most likely has nothing to do with this.

And actually do a FULL tune up. Your missing dizzy cap, rotor, and fuel filter.

JarvisW

Yeah, the Fuel Filter is the only one I didn't change. Its also time for coolant change before it freezes over, so I'll do another burp or two then.

I did put the FITV back together, I followed instructions here somewhere. Been over a year, but it doesn't happen as much when cold, so its not the problem.

I'll change the FF later this week, but will watch for OPs updates too.

thegill13579

Check exhaust back pressure as well, perhaps the cat has been clogged since you mentioned the a/f was messed up before. I had that issue before and it was like night and day when i changed the cat.

RobocracyAlpha

So...changed my fuel filter about an hour ago. Went for a test drive. No improvement whatsoever.

HOWEVER, I the check engine light turned on and I read it as soon as I got home. P0171 and P0170(pending).

Both codes refer to the system running too lean. However I haven't been able to find any vacuum leaks after spraying throttle body cleaner all over my hoses/manifold gasket.

Any ideas on what could be going on?

As far as exhaust back pressure...i don't have a cat. And I have a very wide open muffler(classic fart can). And I can feel the exhaust PUSHing out of the muffler. Hard. Although, sometimes the exhaust sounds extra shitty. And I don't know if it's my imagination...but I think it messes up more when it sounds crappy.

RobocracyAlpha

Also, I don't have an FITV as far as I can tell

RobocracyAlpha

Now I'm popping P0171 and P0170. I doubt it's dizzy cap or rotor. Any thoughts?

RobocracyAlpha

It ended up being a faulty upstream o2 sensor. The sensor passed all diagnostics including multimeter testing. However, it would fail to send correct signal voltage within a very specific temperature range. Found this out by hooking up a data stream tool to the ecu and reading realtime values when the issue occurred. The o2 sensor would hang at 1.27v(deceleration voltage) even after I began to accelerate. The minute the o2 sensor changed voltage...the car would start firing correctly. What I think was happening here was a lazy response to emissions metering that told the ecu that the motor was still decelerating even after I was accelerating, causing a lean mixture because fuel supply wasn't increased to match engine load.

Changed o2 sensor this morning. Went for an hour test drive. No issues what so ever.

For those who read this in the future: if you don't have a nice scan tool that feed realtime data. Simply unplug the upstream o2 sensor so the ecu will revert to the base theoretical fuel/air mix and see if the problem resolves. If it does, it's probably not a bad idea to replace your upstream 02 or at the very least clean your electrical connection to the sensor with some contact cleaner.