Turns over but no start
WHAT ENGINE ?????? 4, 5.2 or 5.9 Liters?
Fuses are First, always for ever. on electrics or EFI.
dry rail cranking ! you must crank it.
(if you have liking injector or leaking regulator it can drop fast ,so crank on) yes, 2 men or 1 and small boy, LOL
so check voltage at the pump cranking. please stop guessing.!
the ECU commands up the PUMP , cranking or running
so crank and read voltages at pump or at FP relay.
pump activating, is by premissives. not just a key on event
due to crash and burn rules. (unlike on TV)
same with injection. (spark must be good)
first , buy your self a voltmeter (DMM/DVM) its a very easy tool to use
and on volts, mode, totally harmless to you or car. !!!
be aware, that on some cars
if there is no spark, there is no fuel pumping
or it might take a second to detect no spark and the pump is cut
or on one of my cars the pump works the engine starts for 1second
and the ECU sees no spark (dead tachometer ) even though spark is
good the ECU sees no spark and ALL fuel is cut, injectors and fuel pump relay ( you never monitored the action of the relay?. and its dead.? i bet?) spark monitoring can fail with good spark, !!!
the path, on all cars.............. pins and colors change to confuse...
the FUEL pump relay is in the PDC
it has 4 pins, its just a 4 pin std, relay.
a coil and a contactor
if the coil is not HOT (12v across the coil) cranking
there will never ever be pump action.
so the first test is to check the PUMP relay coil wires.
the coil hot side is 12vdc key on
the other wire, marked. C20 DB (dark blue?)
it is 12v keyon
and when you crank the PCM grounds this wire and it must go
to 0v, (0.5v max) if not the PCM is in CUT FUEL MODE.
99.999999% sure, its not a bad PCM. see?
if this line dont go low you must find out why the PCM is in cut fuel.
this is pretty easy,its called a scan tool. got one
they only cost $9 (ask)
if the coil is hot at C18 relay pin and 0v at C20
this state the Relay is energized.
so we check pins C16 and 17,of said relay
we check C16 first. its 12v even key off, hot at all times if not, the fuse is blown. (or battery totally dead)
then crank and pin C17 goes hot(note my order of testing, its not random) C17 dead, is bad relay, C17 12v, cranking is dead pump.
C17 is DG/wht wire, (darkgreen.with white stripe?)
if this wire is cut the pump is dead
so is the pump dead, if hot this wire is, and the pump ground wire is cut.
when i say cut that means cut or corrosion,etc.
eg; gross resistance in the path.
takes 4min to show, and longer to type this...
the G305 pump ground black must not be bad. (12v on black wire is just that while cranking)
i will not fully cover PCM permissive on the pump.
but will do so in short.
1: ECU sees spark loss, for any reason.. even when good real.
All ECu do this differently. many read the spark coil primary
wires of inductive (EMF) kickback , on one or all coils.
other cars its just the tachometer signal dead.
2: CMP errors (cam sensor)
3: CKP errors. (crank sensor)
4: TPS stuck at WOT , usually only cuts injectors.. (unflood mode)
ive built and programmed PCMs from scratch and am aware of all pitfalls here. am.
if have the drawings, ask.
or log in to Alldata.com
again, connect the $9 scan tool
crank for 5 seconds. (min) max 15)
does RPM roll from 0 to near 300? no? bingo.
does DTC 340 or 350 store as you crank or release key
and do not turn off key, wait 1 second, see if DTCs are stored
in the PCM looking with any scan tool made..
if yes, BINGO !!!!
Nov 30, 2013 |
1998 Jeep Grand Cherokee