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Power loss while gentle throttle
5 manual transmisson
I have only had this car for a month or two now, just traded it for a Fiat Strada 02 Wink so I know nothing about power going up hills...! haha (thats why Im not too familiar with the common characteristics of the vitara)

I think the car have had this problem for a while, and been standing still for a quite long period... But fresh fuel and filter before I got it. Tried some "injector cleaning additive" - no change at all.

I was thinking about the fuel pressure. So I will look up my alternatives regarding the pressure tester and, remove injectors etc.

RPM with tps (HOT) cant hold a steady 2000 RPM BTW
And thank you again!!
clogged injectors. due to bad fuel? seems to be it.?
try Chevron Techron additive (if you can find it, it's loaded with powerful Benzene) many additives are useless. oil, or Stoddard solvents or other oddities.. (lots of bad ones, either useless or harmful)

if fuel pressure is good. (spec) and varies by Altitude, (the reason for spec, range is that , and mfg variances)

RPM with tps (HOT) cant hold a steady 2000 RPM BTW

do you mean WOT? or HOT? i want both, HOT wide open throttle up hills, in 3rd gear, just and avg. hill not extreme. (no San Francisco, dig?)
the engine puts out about 95 HP at flywheel. MPI engine.

explain what WOT does. on hills, this is full engine load. 100% 95HP.
hesitates and catches up to full power?

im no Additive guy, not at all but if , no pressure gauge, what else is there????
run a bottle of techron through it and pray,


the FSM is clear.


30-37psi, (This range is for altitude unknown) as you rise in ALT. the fuel pressure drops. at rail.

Vitara 16v G16B 5door JLX -94 5 speed. MPI with 4 dirty injectors

if you did the injector balance tests and it failed ,they are dirty
if by wild chance, rare , all 4 are equally dirty (they have 10micron screens inside) then the balance passes but are still cogged. can be.
the balance test (tricky) show that each injector flows the same.
its speed of leak down test.(injector activated)
also leaking injectors are possible, with bad fuel.

can't do MPI work with out a pressure gauge and a NOID lamp, ($1)

you can see the factory book there, using the guage at the fuel rail. (takes special fitting , seen on my pump test page , sold at summit racing, for $10
and can be done at the filter, but the balance test would be a horror there.
I add a scharader valve to all cars. seen with none. it's first thing i do.

here is what some of what ive done and others.

but at least this, part here. is the top way to get progress. with this one part you can fit up what ever you need.


NPT, national pipe thread. (tapered USA spec.)

note how the rail thread size is clearly stated there.. 14mm x 1.5Pitch.

one more fact
when you go WOT., W.O.T , wide open throttle.
the plenum goes to full (near) atmospheric pressure, the PFreg increases fuel pressure, by about 6 PSI.
if not, the engine BOGS HARD, starves for fuel.
this is how it works.
this is why we do all 6 pump tests, all MPI balance test. and 3 tests on the FPREG. or its all a crap shoot.

I had to let a mechanic test the fuel pressure.. about 2.8 BAR and holds steady (on fuel rail). He said no problems and didn't think of any leakage on the injectors.

But he thought the fuel filter could be the issue...

The car answers pretty good above 2500rpm in 3rd gear uphill.(WOT) under 2500 it feels weak (WOT) Have to enter the hill with 2500rpm or gear down
- it doesn't really matter if i go WOT or just 3/4, still as weak so feels like WOT is useless under 3000 rpm uphill
(hope you understand)

Idle fine 800 HOT, with just a single light "exhaust puff/misfire" in a quite regular interval, like puffing a cigarr
I can't hold 2000RPM when HOT it drops to~1000 and up around 2000. drop every 3-5 second and answers itself
* if i handgun the engine to about 2000rpm its just the same. 1 (i think) single misfire/bogg every 3-5s (drop 1000 rpm)
and catches up, followed by another jerk in the interval i said.

But NO misfire/jerk hesitation if I go 3500+ rpm. then it feels powerful and stable
40.6psi (2.8 bar ) wrong, what was key on pressure.? same i bet.
when testing the fuel pressure there are 2 first tests on that page, i have, factory page , keyon, and idle. (id bet this fails) and was skipped
its a 6psi drop

the pressure is only steady at idle and steady cruise.
the pressure most goes up about .4 bar, gunning the throttle and drop fast as you cut throttle (high vacuum) this is the FPReg working.
the fuel pressure follows the vacuum bar, 1:1 one to one. in that , wot, is full (or near) atmospheric pressure, and the fuel pressure rises to meet..
from wot to cut throttle under huge vacuum the fuel pressure can drop a full 1 bar. end to end.
I just use a hand vacuum test gauge to check the FPReg at idle. easy, no driving and testing, under load.

yes,it is running bad. even parked it runs bad.
at 2000 RPM it surges.
(if you unplug the ISC connector, (iac electric) does the surge end? if yes, its the cause and is because the idle switch is set wrong or bad.
if the isc is not the cause, then its bad fuel mix, lean/rich repeat.
we have no scan tool to see if it drips closed loop, hooding , RPM at 2000,, I'd bet it is.
testing EFI blind is not easy.
for example is the PFREG messing up? or is it an input to the ECU wrong, or are the injectors clogged?
very hard to find this with no scan tool.

that is why i check the PFReg very carefully to put it out other 3 ideas list above.

lets look at my graph again.
key on, zero bar, vacuum. and say 36 psi fuel pressure, you start the engine and you pressure drop (fuel) to 30psi)
NO MATTER, where it starts it must drop.
metric. (sadly folks use 3 gauges, world wide, KPA,BAR and PSI..
at 0 bar vacuum the fuel pressure is 36 to 43 psi (varies by altitude and part variances) lets pick 40. (middle) or 2.8bar.
you start the engine and its hot and idle is 800 and the vacuum is now. 0.64bar
if you gun the engine and let it drop RPM fast the vacuum can go to 0.8 bar
the fuel pressure will track with the vacuum bar. 1 for 1. (the ECU is programmed for this GIVEN)
if the PFreg fails, the ECU FAILS to injector right.
ill add bar to the graph.

[Image: reg-graph-mpi-g.jpg]
I understand how it should work. But as I left the car to the mechanic, (I work the same opening times as the mech)
So I left a printed copy of your step by step check outs. But I dubt he did them all. Probably just key on 3 times and yes. 2.8 Bar seems fine. DONE!

The shop really dont put any love in their work, I've heard.

So seems, like I have to get myself a tester gauge.
he may no know how a FPreg works nor just how important it is on older cars. this car has no fuel pressure sensor ,like all new cars have.
the new cars run a fixed pressure, and this reg, based on vacuum is not important on new cars .... they forget or never learned it.
i wish you luck and , a solution fast.

the reg can have a stuck valve. (open or closed or?) many are, this old or temperamental.
the diaphram can crack. and get near 3bar.
if it sticks at say at or near 40 PSI (3bar)
it will over fuel. at most times.
causing rich misfire, normal idle is 2.1bar.

3 bar fuel pressure is only good, at WOT. . (to push hard against the high atmospheric pressure of 1 bar)

btw ,nice write up on symptoms. best ive seen.
Okay,. There is no other way I can check the fpreg? Like blowing/suck the vakuum hose? Smile

I get no reaction (RPM)when pulling the vakuum hose at the plenum, and blocking at plenum...

If I let air in offcourse it reacts.
Can I put any Regulator back in? like this http://www.ridetech.se/bransletrycksregu...lack/413-0
Its an adjustable between 1-6BAR, set it at 3 BAR?
There are adapters included.
if you can suck that hose, and air moves the FPreg is HORRIDLY bad,
only tools can check all features of any FPREG, there is no other way, besides just replacing it.
the vacuum hand pump is $28
the fuel gauge is $20

why put in a racing PFREG at huge expense?? (and i cant read the engineering data sheet so cant really say,,,,) but yes, 1:1 is there. but you'd have to tune it.
then have to tune it, with no tools.>>> why?
the reg must be 1:1 ratio. or the ECU will go quite mad. 1bar vacuum causes 1 bar fuel change. 1 for 1. or FAIL.


the reg is sold at all suzuki
and at rockauto.com

i will not pretend to know what part of your car is bad, only tests prove this.
BAD TPS?, intake vaucuum leaks?, clogged CAT. ? air leaks near the 02? sensor. bad MAF. ? lots and lots of tests there are.
A lot of work lately...!
But I got a new o2 sensor and the bogging is gone! Feels so good.
Car is running smooth and nice!

Thanks for all the help and advices. It helped me to narrow down my problems, and dare to spend money on the new O2!
the old one , was stuck rich or lean, hard over.
most read lean busted (by design), so ECU goes rich and engine misfires. Bosch worked hard to get that to fail that way and not burn up valves. fail safe.
in 1996 this got better , not so rich, not so misfire. (less smog too)

the new cars have what we call rail clamps. that are tighter. and the ECU throws errors, when you hit those rails. FUEL TRIM RAILS>!

thanks for the feedback, its good to see success !!!!

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