1990 Nissan Sentra 1.6L 4speed - followup on stumble during acceleration
robbie
the car seemed like it was losing power, stumbling, low rpms, the car
just seemed like it wasn't getting fuel.
THEN, if you let off and gently accelerate the power is back,
everything is fine. This is repeatable ad infinitum
and is less apparent (sometimes doesnt happen) when the engine is cold
but always present at normal operating temps.
it has good fuel pressure, all 4 injectors work, the fuel pressure
regulator works properly,
the ECU shows 55 - no faults- same as it always does when i crawl
under the dash and check for error codes!
it was recommended to check/replace the engine temp sensor and/or O2
sensor.
For whatever reason, I want to blame the TPS so I tested it according
to the Haynes manual-
I followed the test procedure, and the manual claims it should read .5
-1volt at closed throttle, and 4-5volts at WOT-
well according to my meter MY TPS reads the opposite- at the closed
throttle it reads 4.3? volts and at WOT it
reads 1.1 volts. Have I found the likely culprit? Does the Haynes
manual have it wrong?
Thanks to all who take the time to read!
robbie
al
The problem is clearly being caused by something that depends on
engine vacuum. When vacuum is low, the problem appears and then
disappears when vacuum is high. I'd check the EGR system. Too much
EGR will lean out the mixture on acceleration and cause stumbling and
hesitation. You can test this hypothesis by blocking the vacuum line
to the EGR valve thus disabling the EGR system. If the problem
disappears, you know it's the EGR system. Another characteristic of
EGR system trouble, is that the stumbling/hesitation will not happen
when the engine is cold and warming up but rather begins abruptly at a
very specific coolant temperature during warmup. That occurs because
the vacuum for the EGR system is supplied through a themostatically
controlled vacuum switching valve which only opens above a specific
coolant temperature. Good luck. Al
robbie
the egr valve and giving it a test drive.
Peter Hill
You are testing at wrong place. You are testing between feed voltage
(constant 5V) and output. Test is between output and ground.
Sounds like a fuel starvation problem. Really needs a fuel pressure
test under load. T a pressure gauge in after filter, on a long hose.
Route the hose under back of bonnet and place pressure gauge so it can
be seen from drivers seat.
When I had this problem, I went though the whole fuel system.
Everything pointed to a faulty connection but I couldn't find it. Then
it packed up completely. Power at relay, no power at pump. Then I
found the alarm, dry joint and quite well toasted. Some dork had put a
5A fuel pump circuit though a 2A relay circuit and connectors on the
alarm. Soldered alarm and wired up external relay.
>> > �Thanks to all who take the time to read!
>> > robbie
>>
>> The problem is clearly being caused by something that depends on
>> engine vacuum. �When vacuum is low, the problem appears and then
>> disappears when vacuum is high. �I'd check the EGR system. �Too much
>> EGR will lean out the mixture on acceleration and cause stumbling and
>> hesitation. �You can test this hypothesis by blocking the vacuum line
>> to the EGR valve thus disabling the EGR system. �If the problem
>> disappears, you know it's the EGR system. �Another characteristic of
>> EGR system trouble, is that the stumbling/hesitation will not happen
>> when the engine is cold and warming up but rather begins abruptly at a
>> very specific coolant temperature during warmup. �That occurs because
>> the vacuum for the EGR system is supplied through a themostatically
>> controlled vacuum switching valve which only opens above a specific
>> coolant temperature. �Good luck. �Al
>Thanks for the advice. I will test this out using your theory and plug
>the egr valve and giving it a test drive.
--
Peter Hill
Spamtrap reply domain as per NNTP-Posting-Host in header
Can of worms - what every fisherman wants.
Can of worms - what every PC owner gets!
robbie
retest. Thanks.
On Feb 21, 12:59 am, Peter Hill <peter.usen...@nospam.demon.co.uk>
wrote:
Andrew Chaplin
news:e4725107-bf52-4534...@g28g2000yqh.googlegroups.com:
> Darned Haynes manual! those pictures are never accurate! I will
> retest. Thanks.
If you haven't checked already, inspect any air hoses leading to the
throttle body carefully. If they are cracked and open up when your engine
flexes the motor mounts as you accelerate, then it may be screwing up the
air mixture.
--
Andrew Chaplin
SIT MIHI GLADIUS SICUT SANCTO MARTINO
(If you're going to e-mail me, you'll have to get "yourfinger." out.)
Jim Yanik
news:Xns9D26805F94...@216.196.109.144:
> robbie <robbie....@gmail.com> wrote in
> news:e4725107-bf52-4534...@g28g2000yqh.googlegroups.com:
>
>> Darned Haynes manual! those pictures are never accurate! I will
>> retest. Thanks.
>
> If you haven't checked already, inspect any air hoses leading to the
> throttle body carefully. If they are cracked and open up when your
> engine flexes the motor mounts as you accelerate, then it may be
> screwing up the air mixture.
Heh,they just talked about this on Motorweek yesterday...about the air duct
from the MAF to the throttle body cracking and opening under motor torque.
--
Jim Yanik
jyanik
at
localnet
dot com
robbie
I tried the egr valve bypass and it definitely helped, but there is
still some slight hesititation. I am going to reinstall the fuel
pressure gauge and mount it so i can test drive it while watching the
gauge as someone else has suggested. I am convinced that the egr valve
is part of the problems. Anyone know of any reason (except emissions)
to get the egr system working properly versus leaving it bypassed?
Thanks!
willshak
I'm not sure, but you may have 2 of them (the Pulsar did). One at the
exhaust manifold and one in the usual location, below the drivers seat
If only one, it's in the usual location
--
Bill
In Hamptonburgh, NY
In the original Orange County. Est. 1683
To email, remove the double zeroes after @
Andrew Chaplin
> Andrew Chaplin <ab.chap...@yourfinger.rogers.com> wrote innews:Xns9D26805F94...@216.196.109.144:
>
> > robbie <robbie.h.wil...@gmail.com> wrote in
> >news:e4725107-bf52-4534...@g28g2000yqh.googlegroups.com:
>
> >> Darned Haynes manual! those pictures are never accurate! I will
> >> retest. Thanks.
>
> > If you haven't checked already, inspect any air hoses leading to the
> > throttle body carefully. If they are cracked and open up when your
> > engine flexes the motor mounts as you accelerate, then it may be
> > screwing up the air mixture.
>
> Heh,they just talked about this on Motorweek yesterday...about the air duct
> from the MAF to the throttle body cracking and opening under motor torque.
That is, in fact, where I got the idea, and it may fit with the
problem he's having with his Sentra, especially since it is "stumbling
during acceleration." It's an easy thing to check.
Clive
<92a72995-2d51-40bf...@f8g2000vba.googlegroups.com>,
robbie <robbie....@gmail.com> writes
>I tried the egr valve bypass and it definitely helped, but there is
>still some slight hesititation. I am going to reinstall the fuel
>pressure gauge and mount it so i can test drive it while watching the
>gauge as someone else has suggested. I am convinced that the egr valve
>is part of the problems. Anyone know of any reason (except emissions)
>to get the egr system working properly versus leaving it bypassed?
>Thanks!
up caused by piston blow-by. Doing away with this could cause
crankcase pressure and oil leaks.
--
Clive
cse...@mts.net
wrote:
>In message
><92a72995-2d51-40bf...@f8g2000vba.googlegroups.com>,
>robbie <robbie....@gmail.com> writes
>>I tried the egr valve bypass and it definitely helped, but there is
>>still some slight hesititation. I am going to reinstall the fuel
>>pressure gauge and mount it so i can test drive it while watching the
>>gauge as someone else has suggested. I am convinced that the egr valve
>>is part of the problems. Anyone know of any reason (except emissions)
>>to get the egr system working properly versus leaving it bypassed?
>>Thanks!
No. Your thinking of the PCV valve, The EGR recirculates exhaust
into the cylinders to lean out the mixture, warm the incoming air, and
cool the burn so as not to burn valves
>The EGR system helps purge the crankcase of fumes and any pressure build
>up caused by piston blow-by. Doing away with this could cause
>crankcase pressure and oil leaks.
>--
>Clive
>
--- news://freenews.netfront.net/ - complaints: ne...@netfront.net ---
robbie
> On Fri, 26 Feb 2010 16:13:31 +0000, Clive <cl...@yewbank.demon.co.uk>
> wrote:
>
> >In message
> >robbie <robbie.h.wil...@gmail.com> writes
> >>I tried the egr valve bypass and it definitely helped, but there is
> >>still some slight hesititation. I am going to reinstall the fuel
> >>pressure gauge and mount it so i can test drive it while watching the
> >>gauge as someone else has suggested. I am convinced that the egr valve
> >>is part of the problems. Anyone know of any reason (except emissions)
> >>to get the egr system working properly versus leaving it bypassed?
> >>Thanks!
>
> No. Your thinking of the PCV valve, The EGR recirculates exhaust
> into the cylinders to lean out the mixture, warm the incoming air, and
> cool the burn so as not to burn valves
>
> >The EGR system helps purge the crankcase of fumes and any pressure build
> >up caused by piston blow-by. Doing away with this could cause
> >crankcase pressure and oil leaks.
> >--
> >Clive
>
UPDATE: Thanks for the multiple threads of advice- ALMOST too much to
try to troubleshoot!
1st- the TPS i tested correctly to ground and it indeed does test
from .49v (closed throttle) to 4.25v (WOT) so I am ruling it out.
EGR valve- disconected and plugged it, and i thought it was improved
but after driving for more than a few minutes it has same symptoms-
starving at WOT-
i applied vacuum to the EGR while the engine idled and it is
definitely working- engine nearly died from lack of fuel.
fuel pressure- I put a t-connector in after the fuel filter, and
mounted it where i could watch while driving- it never got below about
35-38 psi,around 44 average-
even at WOT-but I would like someone else to comment on that- what
SHOULD the pressure be at WOT? according to Haynes the max pressure of
the pump is 65 but there is no "max pressure at WOT" specification.
if the fuel pump is just getting old then someone chime in!
After finding nothing major i was retesting all the piping/vacuum
hoses/intake plastics etc looking for a leak that could cause my
symptoms. also unplugged and replugged Idle Air Control and a few
other sensors. then i test drove some more and the Check engine light
was flashing intermittently - at idle and at speed, and would mostly
stay off, but i was kind of elated to see it. So i immediately pull
the ECU out from under the center dash console area and check the
codes and get
VERY annoyed- still reading 55 - all systems check ok- so obviously
the check engine code doesnt stay around long enough to be logged in
the ECU! DANG DANG DANG! all right, I have ranted enough- let the
suggestions begin again- and someone who knows about the fuel pressure
- is that enough fuel for WOT or is that where my problem lies? Thanks!
Peter Hill
Mode III faults that result in non 55 code tend to be gross faults
like something unplugged or shorted. When the code isn't 55 the check
engine light will be on.
Some Nissan ECU's have a mode V - dynamic test. Doesn't store any
fault for mode V faults. The flash pattern indicates which system the
fault is in.
Sorry I don't have this data for Sentra 1.6, only UK/Euro '89-94
CA18DET. Sentra may be different.
CAS missing pulse - even spaced slow flashes on 1.6sec off 1.6sec.
AFM momentary spike in output, 2 flashes then a gap, on 0.6sec, off
0.4 sec, on 0.6sec, off 1.6sec.
Ignition - signal from primary coil drops off, 4 rapid on/off 0.2 sec
flashes, 1.8sec off.
These faults can usually be traced to poor connections, tap tests are
suggested to locate.
al
>
> - Show quoted text -
Have you measured manifold vacuum? It should be 18-20" Hg at idle and
more importantly, it should be very stable. It should drop as
throttle opening increases and should not be fluctuating wildly. If
all of that is normal, I'd go back to the EGR system. You said that
when you disabled it, things got better. If everything else checks
OK, that's the only cause/effect relationship you have. A very lazy
or a partially stuck open EGR valve, especially if there's a vacuum
leak at the gasket between the EGR valve and the intake manifold,
could be the problem. Good luck. Al
robbie
One other thing I have confirmed through multiple test drives- the
symptoms do not occur at startup- they begin when normal operating
temperature is reached.
when cold the acceleration is strong and uninterrupted by any
stumbling or hesitation whatsoever. so whatever is occurring is
temperature dependent. i believe someone mentioned temperature sensor
a while back on another thread- are there more than one temp sensors?
my temp gauge works correctly by the way.
Peter Hill
<robbie....@gmail.com> wrote:
> are there more than one temp sensors?
>my temp gauge works correctly by the way.
Yes there are 2 temp sensors. One single wire one for temp gauge and a
2 wire one for the ECU. Both will be on the thermostat housing.
al
>
> - Show quoted text -
The fact that the problem does not occur during warmup points to a
system that depends on ported engine vacuum. The EGR is one such
system. The vacuum for the EGR valve is typically ported through a
thermostatically controlled vacuum switch which only opens above a