Question about 1995 Geo Prizm

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95 prizm w 1.8 bucks and surges from about 2000 to 3500. fule pressure is dead on, map tests ok ,injectors omh out good,no vaccum leaks. have all so replaced distributor w a known good unit. has new cap , rotor wires and plugs as well

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  • deniohio Nov 17, 2009

    idle is smooth , and it accelerates up to 2000 smooth as silk , and it wont act up till it is up to operating temp, when cold it accelerates breat

  • deniohio Nov 17, 2009

    idle is smooth , and it accelerates up to 2000 smooth as silk , and it wont act up till it is up to operating temp, when cold it accelerates great

  • deniohio Nov 17, 2009

    vaccum gauge holds steady, needle dosnet bounce

  • deniohio Nov 18, 2009

    it does fluctuate with the miss fire,runs about 15 to 20 inches of vaccum

  • jz auto May 11, 2010

    put a vacum gauge on the car. if it bounces all over the place you probably have a vacum leak. does it do this at idle?

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Does the vacum gauge hold steady when this is happening?

Posted on Nov 17, 2009

  • jz auto Nov 18, 2009

    you may have an intake valve thats sticking when the car is warm if everything you checked is right

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Why is black smoke coming from tail pipe


It's running rich , to much gas is getting into the cylinders . Leaking fuel injectors , a fuel pressure regulator leaking , or the PCM is supplying to much fuel to compensate for a problem that it think's exists. an O2 sensor stuck lean , a bad or dirty mass air flow sensor . Is the check engine light lit ? You should take it to a repair shop an have diagnostics run on it !

Sep 22, 2015 | 1994 Geo Prizm

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How do i fix a 91 isuzu truck manual trans. 2.5L that u start and is all good to start as soon as engine runs its running at high rpms.


old car, very old
this is easy, to find, but can be many things, my tests cut this to 2 reasons. mostly. (leaks and isc failure tests)
1: ISC system is dead, (stuck idle speed contr. valve)
2: throttle cable stuck or set wrong, (must have slack)
3: vacuum leaks, on all cars with map sensors, vacuum leaks make the ISC loose control and RACES fast with full engine power. all MAP based EFI SYSTEMS, "speed density systems:

Sep 08, 2015 | 1991 Isuzu Pickup

2 Answers

Injector sprays too much fuel after starting. Engine floods out


Suspect (potentially) either a stuck injector, or a failed/failing fuel pressure regulator. One sign of a failed fuel pressure regulator can be gas in the oil. (I suffered that side effect, along with bogging, and black smoke rich running, worsening as warmed up, turned out to be fuel pressure regulator). If the injector is loose in the throttle body, or has bad o-rings, can also cause some wonky behavior. Good luck.

Mar 14, 2015 | 1992 Geo Tracker

1 Answer

2004 jeep wrangler 2.4 motor bucks on hills.


W.O.T. MISFIRE< that is what you have.!
is the CEL lamp glowing running , and for sure WOT?
yes, then scan it, get the codes, P0300? P030x? what is it?
DON'T NOT IGNORE THE CEL,
hell, id scan it and look for pendings,!!! and freeze frame fails.
i would, id not leave that stone unturned, not me....ever.
it is the first after a tuneup full, i look for troubles even marginal.

Ever to a full 60,000 mile tune up? (fuel filter?) not just plugs?
spark wires, see the list. , ,wires and plugs and filters.. skip this service, means long hard and difficult troubleshooting.


2.4L I4,
if fuel pressure is good on hills its not the pressure side. 49psi.
but the car has a fuel pressure regulator, and we test that at the pump test, its part of pump, if not skipped. with gauge, we make dang sure it regulates.
new fuel pump , means zero to me
49 psi pressure now that matters, what if the reg is bad or the
12v power to pump is 6v, bad.
and not doing the leak down test at the pump pressure
test , misses the injectors leaking, or the balance test shows
clogged injector on say #1 . (not equal)


Real tune up done, and no DTC errors store, or pending.

only hills, can be
clogged injectors
MAP reading wrong, (clogged vacuum input to it)
when you WOT the throttle (wideopenthrottle) the MAP pin1 voltage
changes to 1Bar, (atmospheric, or 0 vacuum)
see page 31 in fuel system section of FSM.
the page is weak, no graph, but 0v (near) is very high vacuum and
4.6V at WOT, sea-level reading)
using absolute pressure method not vacuum (which i like)
is 0v is zero pressure (huge vacuum)
is 4.6v at full atmospheric pressure wot, the butterfly TV is wide open.
at keyon, no start the map is at atmospheric, pressure, 14.7PSI
or 1 bar, pressure. (about)
so if you monitor the mAP voltage output and it goes new 0v at WOT
then its done its job. an the misfire is caused by other reasons.
just one voltage test, and bam. not MAP or clog there.
i check map key on, idle and wot. 3 readings. to prove good maps.
in most cases the clean map works every time. see that its nipple
end is clean, (vac, port)


the ecu reads the MAP and the IAT temp, and computes AIR FLOW
and MATCHES that. with 12.5:1 Air top fuel ratio.
(fuel injections works just like this on Speed Density Systems)

and makes full power. if spark is good, and compression is good.


if the injectors are clooged, it misfires, if the spark plugs foul, missire
if the injectors leak, again, misfire.
that is how it all works, cept the magic fuel; tables in the ECU.

the scan tool ECT showing, 180F or more holding hot engine?
no , then thermostat is bad and AFR is rich as heck.
Is IAT reading odd? not equal to ECT first check key on , in morning not started, is bad IAT. they become equal as you sleep. overnight
the air temp matches the water.... a very easy trick this test.
by careful observation, key on, no start.
the 2 sensors report in , even key on,. all the time.
using any scan tool (not old)


Feb 03, 2014 | 2004 Jeep Wrangler

1 Answer

1992 isuzu pickup,2.6 engine , surges up and down after 10 minutes then shuts off


1992, PICKUP, in USA? what country , ? cars are not same all over earth. sorry.
engine surges, then stalls. correct.>?

nice testing , rare here, real nice !!!!
spark good as it stalls
so if engine is ok, compression, (seems cat is not melted with 20 " HG)
is flooding or starving for fuel,.
one or the other, you can find that out.
if spark timing was ok, then the belt did not slip. on cam)
leaving only fuel issues.
so DO the magic , WOT, cranking trick this trick (logic in ECU)
cuts the injectors dead, cranked, to unflood all engine with EFI.
do that?
check spark tips, for 3 to 4 hours dead.? be next
2.6L (is 4 cylinder.) is cam belt drive, i never fail to check it first
the fail, at 60k miles, all do. all rubber band engines do.,

if all this is ok, not flooding
one can start engine with test fuel, and even keep it running
even with (hint) fuel pump relay pulled.
if that works, the fueling is wrong.
injectors leaking,? ?
if only one spark tip is wet , soaking in fuel, Injector issues.

when it stalled pull all 4 plugs and look at the tips.
(if cam is timed right) be super super first thing, on this 4 banger.

Mar 08, 2017 | 1992 Isuzu Pickup

3 Answers

I have a 2005 Ford Taurus. I got my car checked out at Auto Zone and the code said that the number three cylinder was misfiring. I have changed the oil, had a tune up,( new sparks plugs, fuel and air...


First off I think it's time for a new mechanic. Doing an oil change and replacing the fuel filter and air filter have nothing to do with a misfire. Spark plugs and ignition coils can cause a misfire, but a good mechanic will test the coil and inspect the plugs instead of just guessing. Your mechanic is guessing and just throwing new parts at the car. A misfire can be caused by (aside from a bad coil or plug) a faulty or clogged fuel injector, spark plug wire, wiring to the injector or a vacuum leak. Since you only have a misfire in one cylinder, and you hear a whistle on acceleration, I would suspect a leak in the intake manifold. Go to a reputable repair shop and have them check the manifold for leaks. You can also check yourself by buying an automotive stethoscope, and moving it around the perimeter of the intake manifold listening for a hissing sound. Or have someone press on the gas while listening for a hiss under the hood.

Mar 11, 2011 | 2005 Ford Taurus

2 Answers

What would cause an inconstant miss in a 95 geo prizm? we have changed the plugs and wires, main brain box, map sensor and the ecm. what else could it be?


Find the cylinder that is missing,and check the compression on the cylinder.If the miss is not narrowed down to one,or two cylinders,then run a compression test on all the cylinders,if while testing one cylinder,and the gauge fluctuates up and down,then check the one next to it,it it also is doing this,then the head gasket is leaking compression into one another.

Jul 07, 2010 | 1995 Geo Prizm

1 Answer

Engine surges under load at 3800 rpm


yes it could be. have fuel pump pressure tested, fuel pump pressure should be. (key on engine off) 1999 to 2000--with egr--41 to 47 psi without egr--52 to 58 psi,

May 30, 2009 | 1999 Pontiac Grand Am GT

1 Answer

1988 F15 4.9L RUNS LIKE IT IS MISSING


One more thing when you check the timing did you pull the vaccum plug that will turn off vaccum. The plug is located next to the distributor looks like a dead plug with two wires running to it pull the plug spout out and recheck.

Apr 23, 2009 | 1988 Ford F 150

1 Answer

95 geo tracker runs fine but bucks or surges at 25/30 mph slow cruise accelerates like rocket.


8valve or 16v valves, big diff !

bucks, needs a tune up.
surges are too lean .
for surge check fuel pressure.

i think you mean Wide Open throttle has full power
right.?

if yes , the fuel pressure is ok
and the MAF is bad on a 16v
or you have an air leak.

tell more , get more.

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