hot engine or cold, or both????
no engine stated, this the I6? 4.0L inline 6? we dont know.!
can it be driven?// or its a dog.?? or stalls? or???
why did you not scan the PCM first.??????????
back fire?, this can be the following (text book true)
1: burned intake valves.
2: cam timing way off
3: spark timing way off.
4: or running super lean and aggressive throttle actions..
its a 1998 Jeep.
does it run? sure and badly....its misfiring, i bet. not just bogging.?
and long enough to see the CEL lamp go out?
if the CEL is on, running that means scan it,
in the USA< all scan tools work. why not scan it.?????????
why are you replacing parts. are you rich?
what id do is do the 3 classic tests.
compression, spark, fueling.
in that order , going backwards is long hard row to hoe. for sure.
compression at 150psi, or more on all cylinders.? at wide open throttle. ( a $20 tools, dirt cheap and 30min work)
alldata.com has the full spec. on that .
as does here.
if compression is good.
i whip out my $20 strobe light and check spark timing at #1
(open hood , look up, see that EPA spark time spec there? bingo.
if way off, find out why. now. do not proceed.
i then scan the PCM. with any scan tool. got DTCS? post them.
The PCM will report misfire, why not let it tell you?
as will it tell you the CMP or CKP are bad or misfiring, it WILL.
why not let it.? the JEEP will report the CKP misfire with 1 in 10 pulses. so
engine now will run and sound good on test fuel with fuel pump disabled. ( it runs for 3 seconds over and over an sounds good.)
i put back the Fuel pump relay and proceed with bad fueling
the #1 test is fuel pressure.
if the fuel pressure is low , way below 28psi no EFI works.
so that is first. and the ECU can not know its low, so injects weak.
all cars like this do that.
not only that the JEEP will drop the ASD relay if spark is bad orCMP,or CKP are bad . stalls instantly. i will.
no engine stated so no fuel pressure spec stated. sorry.
With the fuel pressure gauged atteched, (one more $20 tool)
i then do the injector leak down test. next. (pressure is good)
text book ways, if the pressure drops, it can be a leaking injector.
we check that very carefully.
then we do the injector balance test,(text book) ask. how.
the balance test checks for each injector to drain same as the others.
we activate the injector and watch it leak down.
i have a video of a famous youtube , shop doing that.
the balance test has 2 methods, using an injector pulser.(tool)
or the more tricky way of using the PCM /ECU to do our bidding
lets talk about that., the ecu pulse all injector cranking
so i key on until i have full line pressure.
i then unplug all injectors (electric plug) except say #1
i then pull the fuel pump fues at max psi, and crank down the pressure. but some jeeps cut all injection when the pump power is lost. so on JEEPS that have and ASD relay the trick is near impossible to do.
Some folks use 9vdc smoke detector battery to power the injector.
for a few seconds, this protects the injector from overheating
some injectors do not like full time 12v across there pins.
so you key on to get full pressure. then key off
pressure holds (the leak down test above passes)
then apply 9v to the inject and count the seconds until it leaks
down and stops. this is the injection rate.for #1
repeat on each injector, and compare them.
if one is dead or weak , its bad, clean it.
this is the only way to check injectors on cars.
the alternate is to send them all out for full cleaning
i get mine from here.
ok all the above is good, and it misfires, or what ever.
the order above is the only order that works every time.
lets pretend there are no DTCS running (id bet that is not true.!!!)
i then connect my scan tool. and watch all sensors.
and makes sure they all read correct.
the first sensor is the MAF
but the jeep ,bless its heart has no funky expensive MAF>
it uses a MAP, for speed density systems. (not air mass)
this post is long, its for you and others tracking(have many)
So i start the engine, no DTCs
and look at the all sensors. to they all make sense?
say ECT reads (and IAC) near last nights ambient temps?
yes, good, say it was like 50F last night and first thing this AM
the 2 sensors match, at say 60F>
you start the engine and the CEL goes out and the
ECT rises fast and hits 180F and the IAT will be near about 100F
The IAT depends on its location, i just make sure it rises a bit.
the IAT is a critical sensors on all JEEPS and all Speed Dens. sys.
this sensor is used to calculator air mass. and temp is critcal.
if say the IAT reads too hot, say 100F on cold day the fuel
mix will go very lean and backfire.
THE ECT TELLS THE PCM what mode engine is in, cold, warm or hot.
I then look to see if the ECU/PCM reaches and holds closed loop
at idle. hot. (min dies it in 30second or less)
if not , i fix this first. (MAP readings and tests are next)
I will stop here, as the tests to do next depends on what is wrong now.
and im sure you found it already. DTCs or the test fail.
all this is text book ways. no guessing, all paths to success.
the path is called gathering evidence. (tests)
see Duane do his tests. (misfire)
here is Duane doing the balance test.
keep in mind, bad injectors, bad ECU, bad wiring can cause
any injector to fail, (leak,stick on, or die)
Duane's training videos are some of the best on the web.
note the ASE patch !!!
Good engine, good spark, good injectors, good fueling.
The ECU inputs must be good, or fueling will be wrong.
we do check all inputs now if the above is ok.
its ok to check all sensors first, with the scan tool at the get go
it takes me , about 5min to do that, as the engine warms.
when at 180F ,im dont looking, in most cases.
that is it , unless you have scan data.
a scan tool can be had for $9 off fleabay.
or better for newer cars a 3160 from Innova.