Honda Car Forum

andrew m. boardman wrote:
> Thanks again for the replies; sorry about the long delay in answering the
> latest. (Some unexpeted travel, then some unexpected getting-sick.) I'm
> back under the hood of this thing, though, so here are replies to
> suggestions that were offered while I was in la-la land:
>
>> also, make sure your "hard" idle setting is correct - disconnect the
>> eacv plug and set idle for 750 with the throttle body adjusting screw,
>> just like it says in the honda manual.
>
> It's within spec, though that spec is 625rpm (+/- 50) in my Honda manual
> with the EACV unplugged and no load, 750 with the EACV plugged in.
> (Well, sometimes it does 750 just fine, sometimes it does 1800+.)
>
>>> Unfortunately, the coolant level is good, overflow isn't dropping after
>>> use,
>> but it should! level in the expansion [overflow] bottle should go down
>> as it cools. and you /did/ check inside the radiator, not just look at
>> the bottle? need to be sure...
>
> Sorry, I meant it wasn't dropping between checks with the engine cool.
> The overflow bottle fills up an inch or two when the engine is hot, then
> goes back down when it cools. I did indeed check the radiator (full up)
> and the bleed point (bleeds, no bubbles) after driving. I've also just
> put another thousand miles on it, which I'd hope would chase any bubbles
> out.
>
>> i read before that you disconnected the temp sender, but there are three
>> on this vehicle: one for the radiator fan, one for the gauge on the
>> instrument panel and one for the ecu - just check you have the right
>> one.
>
> I do believe so. "TW sensor" per the book, 20k ohms cold and a few
> hundred hot, just under the distributor, six blinks on the ECU when it's
> disconnected. (But even disconnected and blinking, the ECU pops the EACV
> mostly open from time to time.)
>
>> I don't know if you have a Fast Idle Valve, but on multi-port cars this is
>> the prime culprit.
>
> Nope, no Fast Idle Valve. (Also not multi-port; throttle-body injection
> with stacked main and and aux injectors.) I do have a dashpot diaphragm
> that cracks the throttle during cranking, but that's not misbehaving
> either.
>
> New data after 1k+ miles: I'm really confident the coolant system is
> bubble-free. Mileage is definitely down the toilet, though, so it
> appears that the ECU is not only opening the EACV but increasing injector
> opening as well, which makes me think one of:
> - throttle angle sensor (ECU is seeing "full open" when it's not)
> - crank position sensor (ECU is seeing "high RPM" when it's not)
> ...even though neither of them is far enough off for the ECU to indicate
> an error.
>
> Side question: the Honda manual says "replace throttle angle sensor" if
> it's bad. It doesn't have instructions for doing so, though, and a quick
> look at the sensor on the throttle body shows what looks like a pair of
> rivet heads. Is this actually replacable without swapping the entire
> throttle body?
>
> I've got a friend coming by with a multi-channel digital recorder this
> weekend; we'll wire up *all* the ECU inputs plus the EACV control and see
> what corresponds to the EACV getting thrown open.

wow, that's serious stuff! i love toys like that. keep us posted on
how it goes.

regarding throttle angle sensor replacement, it's actually quite easy.
if you're skilled, you can even remove it without removing the whole
throttle body. use a chisel to nick the edge of the shear head bolts
[the things that look like rivets], then use the chisel at an angle on
one edge to tap them free. then they'll unscrew by hand. i replaced
mine with m5[?] allen bolts. carefully mark the position of the old tas
before removal, obviously. there's a more detailed write up here that
google will reveal.

Oops. This is pretty old news at this point, but better late than never.
(I found many a similar problems in the archives, but there was never any
followup once it got fixed; perhaps this will help someone down the line...)

jim beam wrote:
>andrew m. boardman wrote:
>> I've got a friend coming by with a multi-channel digital recorder this
>> weekend; we'll wire up *all* the ECU inputs plus the EACV control and see
>> what corresponds to the EACV getting thrown open.
>
>wow, that's serious stuff! i love toys like that. keep us posted on
>how it goes.

Sadly, "how it went" involved my friend's nice laptop blowing up, so I
don't have any lovely eight-color graphs of engine sensors over time to
put on the web.

We did, however, find the problem: it was the throttle angle sensor after
all. The reason we didn't catch it the first time is that the arm had
shorted to the +5 side, but the resistance readings between the ground
side and the arm (which is what we checked) were perfect. Electrically,
this didn't raise any error with the ECU because everything that was
being reported was within spec, but it was all compressed into the upper
part of the range of valid TAS readings. Thus, the ECU thinks I've
always got the throttle way open and opens up the EACV and dumps in lots
of extra gas to suit.

>regarding throttle angle sensor replacement, it's actually quite easy.
>if you're skilled, you can even remove it without removing the whole
>throttle body.

Indeed! It was a bit of a lousy angle, but I got in there with a Dremel
and it took only moments. I'm at a loss as to why Honda doesn't consider
this a replacable part.

Sadly, the bottom end of the engine started falling apart after another
few thousand miles, but I'm not completely unhappy with getting 380k out
of it. (One owner since new, no real work beyond the occasional valve
check and oil changes every 8k or so.) The same throttle body is on the
new engine and is working perfectly. (I may get around to posting
pictures of what the bottom end looked like once I have it apart; while I
went for a new engine I've saved the old one.)

andrew m. boardman wrote:
> Oops. This is pretty old news at this point, but better late than never.
> (I found many a similar problems in the archives, but there was never any
> followup once it got fixed; perhaps this will help someone down the line...)
>
> jim beam wrote:
>> andrew m. boardman wrote:
>>> I've got a friend coming by with a multi-channel digital recorder this
>>> weekend; we'll wire up *all* the ECU inputs plus the EACV control and see
>>> what corresponds to the EACV getting thrown open.
>> wow, that's serious stuff! i love toys like that. keep us posted on
>> how it goes.
>
> Sadly, "how it went" involved my friend's nice laptop blowing up, so I
> don't have any lovely eight-color graphs of engine sensors over time to
> put on the web.
>
> We did, however, find the problem: it was the throttle angle sensor after
> all. The reason we didn't catch it the first time is that the arm had
> shorted to the +5 side, but the resistance readings between the ground
> side and the arm (which is what we checked) were perfect. Electrically,
> this didn't raise any error with the ECU because everything that was
> being reported was within spec, but it was all compressed into the upper
> part of the range of valid TAS readings. Thus, the ECU thinks I've
> always got the throttle way open and opens up the EACV and dumps in lots
> of extra gas to suit.
>
>> regarding throttle angle sensor replacement, it's actually quite easy.
>> if you're skilled, you can even remove it without removing the whole
>> throttle body.
>
> Indeed! It was a bit of a lousy angle, but I got in there with a Dremel
> and it took only moments. I'm at a loss as to why Honda doesn't consider
> this a replacable part.
>
> Sadly, the bottom end of the engine started falling apart after another
> few thousand miles, but I'm not completely unhappy with getting 380k out
> of it. (One owner since new, no real work beyond the occasional valve
> check and oil changes every 8k or so.) The same throttle body is on the
> new engine and is working perfectly. (I may get around to posting
> pictures of what the bottom end looked like once I have it apart; while I
> went for a new engine I've saved the old one.)

great followup andrew - closing the loop on problem solution is a
wonderful thing to anyone searching the archives. also, i note the fact
that you're standard transmission, not auto. i suspect that shifting
wears the tps a lot more on the sticks than the autos.

shame on the old motor - what replacement did you use? jdm?