'90 Civic: Extremely sluggish low-end acceleration, poor fuel economy

TeGGeR® wrote:
> "Elle" > wrote in
> nk.net:
>
>
>
>>You and I continue to disagree on this. A guzillion web sites back up
>>my (along with like every other regular's) position on this.
>>
>>
>
>
>
> I just tried two experiments on my own 1991 Integra just now.
>
> -----------------------------
>
> Firstly, I tried plugging the PCV hose shut. The idle dropped momentarily,
> then climbed smoothly back up to 750 and remained there.
>
> When I let go of the hose, the idle surged briefly, then settled back to
> 750rpm. As expected, the engine management system was adjusting air flow to
> achieve correct idle speed.
>
> -----------------------------
>
> Secondly, with the car fully warm, I unplugged the PCV valve hose at the
> pipe where it enters the intake manifold, so the PCV intake was completely
> open as a massive air leak into the intake downstream from throttle plate.
>
> The idle dropped momentarily, then began smoothly surging between 1,000rpm
> and 2,500 rpm. As expected, the engine management system, crude as it is,
> was attempting to adjust the mixture to be correct. The air leak being too
> great, however, it was unsuccessful in doing so.
>
> (Interestingly, air flow from the PCV valve itself stopped dead, suggesting
> that ambient air pressure was keeping the valve shut. IOW, crankcase
> pressure was lower than ambient.)
>
> I then plugged the PCV intake pipe with my thumb, mimicking a plugged PCV
> valve. The idle returned to a smooth 750rpm and stayed there.
>
> I discovered that I could uncover up to a quarter of the PCV intake pipe
> before the idle began surging again, the severity of the surging directly
> related to the amount of exposed intake pipe.
>
> -------------------------
>
> Conclusion: Cars with engine management systems do not suffer noticeable
> problems from a plugged or stuck-open PCV valve unless an extremely unusual
> situation is present.
>
> History:
> I once had a 1975 Toyota Corolla with a carburetor and no feedback system.
> This car would not idle at all with the PCV valve removed. Unlike the
> Integras's feedback system, the carburetor was unable to compensate for the
> excess air. I discovered this quite by accident when an aftermarket PCV
> valve came apart on me.
>


plugged pcv can be compensated, just as you describe, but under load,
especially under heavy load, you /really/ want that thing working
properly. experiment with a hose clamp if you want to test.

Elle wrote:
> "Bruce" > wrote
>
>>Well, I'm going to change the PCV just because I kind of doubt the
>>previous owner put in an OEM Valve, IF he changed it at all. One less
>>thing that could be causing my mileage problems, and it probably needs
>>done anyway.
>>
>>But, I'd also like to check the timing... any advice on finding the
>>timing mark on the crank pulley? I assume it's just a little dab of
>>paint and that I'll have to put some white-out on it to make it visible
>>with the timing light, but I can't see ANY mark on the pulley. Nada.
>
>
> Like Jim said, it is hard to see. You should go at it from the top, and with
> a flashlight, using the directions he gave.
>
> That degreaser you applied may have helped shorten the life of the pulley's
> timing paint marks. The marks are mechanically etched into the pulley,
> though, so they should still be somewhat visible.
>
> You do realize it's four marks, all within about 10 degrees (too lazy to
> think about the exact degrees apart they are), right?

i'm not sure the 90's do. my 89 does, but my 91 crx didn't - it just
had a single mark - and i did check! i think this is because at about
this time, the newer timing lights came out with adjustable advance
angle. just set the degrees you want on the timing light and adjust the
tdc mark accordingly. with the 4-mark system, you can use an older
style non-advance timing light.

>
> There was a photo online of the c. 90 Civic's timing marks at a certain site
> that I'm trying to pull up now. My Chilton's has a drawing and photo, so
> Autzone.com and probably the UK site should have at least the drawings, too,
> under "ignition timing." I'll post a link if I find it.
>
>
>>And I need to short the contacts under the kick plate in the passenger
>>compartment to disable the auto-timing adjustment too, right?
>
>
> Yes.
>
>
>

jim beam > wrote in
:


> plugged pcv can be compensated, just as you describe, but under load,
> especially under heavy load, you /really/ want that thing working
> properly. experiment with a hose clamp if you want to test.
>
>



Absolutely, for preventing the pumping of junk into the intake, the PCV
valve is 100% essential. At WOT is when you stand the greatest chance of
oil getting pumped into the intake even with a correctly-functioning PCV
valve. At WOT and high revs, blowby is going BOTH ways, both through the
PCV AND through the breather.

But for simple air/fuel management, it's not a big factor at any pressure
differential. Especially OBD-II cars are more than capable of compensating
for PCV problems, both leaks and restrictions.

By the way, I just tried the same thing on our '99 Tercel:

1): The hose-plug test was identical to the Integra, except that the idle
never dropped. It appears that the Tercel's engine management system is
faster than the Integra's, and responded too quickly for the idle to drop.
Idle remained the same.

2) When I pulled the hose off the intake, creating the same massive air
leak I had subjected the Integra to, again the idle did not drop, but
immediately began a surge cycle. The Tercel has no tach, but it did not
seem to rev nearly as high as the Integra, and its cycle time was about a
half-second instead of the Integra's full second. The idle settled down
immediately once the pipe was plugged with my thumb.

I discovered I could uncover fully half the exposed intake pipe before
cycling began. Slowly uncovering the pipe resulted in a steadily INCREASING
idle until surging began. Half of the intake pipe appears to be roughly
what would be admitted by the PCV valve itself at full-flow.


--
TeGGeR®

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/

"jim beam" > wrote
> Elle wrote:
magnificent snipping, something some people, whom I will not name but whose
initials are J.B., should try ;-)
> > You do realize it's four marks, all within about 10 degrees (too lazy to
> > think about the exact degrees apart they are), right?
>
> i'm not sure the 90's do.

My 1991 Civic does.

The UK manual for the CRX, claimed to cover 1988-1991 but also in places
indicating it may be just for 1988, also shows four marks.

The UK manual for 1995-97 Civics shows four marks.

> my 89 does, but my 91 crx didn't - it just
> had a single mark - and i did check!

Sure. I believe you. A few perhaps pertinent observations:

The CRX is not identical to the Civic. (I assume you know this, but I wanted
to clarify for the original poster.) For example, on the CRX, the "ignition
timing adjusting connector" that needs to be jumpered is in the engine
compartment on the CRX. It's in the passenger footwell on my Civic.

My Chilton's manual has two drawings, covering the 1984-1991 Civic/CRX/del
Sols, showing four marks. But it also has a photo showing one mark.

The online UK manual for 1990-1994 Concertos shows five marks...

I'm betting the OP's 1990 Civic crank pulley has four timing marks.

Elle wrote:
> "jim beam" > wrote
>
>>Elle wrote:
>
> magnificent snipping, something some people, whom I will not name but whose
> initials are J.B., should try ;-)
>
>>>You do realize it's four marks, all within about 10 degrees (too lazy to
>>>think about the exact degrees apart they are), right?
>>
>>i'm not sure the 90's do.
>
>
> My 1991 Civic does.
>
> The UK manual for the CRX, claimed to cover 1988-1991 but also in places
> indicating it may be just for 1988, also shows four marks.
>
> The UK manual for 1995-97 Civics shows four marks.
>
>
>>my 89 does, but my 91 crx didn't - it just
>>had a single mark - and i did check!
>
>
> Sure. I believe you. A few perhaps pertinent observations:
>
> The CRX is not identical to the Civic.

it is mechanically and electrically.

> (I assume you know this, but I wanted
> to clarify for the original poster.) For example, on the CRX, the "ignition
> timing adjusting connector" that needs to be jumpered is in the engine
> compartment on the CRX. It's in the passenger footwell on my Civic.

it's in the passenger footwell of the 91 crx.

>
> My Chilton's manual has two drawings, covering the 1984-1991 Civic/CRX/del
> Sols, showing four marks. But it also has a photo showing one mark.
>
> The online UK manual for 1990-1994 Concertos shows five marks...
>
> I'm betting the OP's 1990 Civic crank pulley has four timing marks.
>
>
maybe it's a peculiarity of japanese imports vs. canadian imports?

the only difference at the end of the day is $20 - the difference
between sears' standard "fixed" timing light & their angle advance model.