98 gmc 4.3 ..61lbs. fuel pressure, good spark, good compression. tries to start and might run for 4 or 5 seconds. if it dosen't start it back fires when you let off the switch. doesn't even want to run on starting fluid. any ideas?

ever see the truck run perfect before, or not in 10 years?
C2500 right not k2500 ,pickup.
NO ENGINE told ,4 engines 3 gas 1diesel.
but is gas so 4 engine not told (no fun there, blind)
4.7 to 5.7L and 5.4L gas.
crankshaft and cam forgot to say sensor?
CAB means distrib CAP .
rotor sure.
why not new SPARK PLUGS first and for sure those ratty old HV spark wire, useless, I run NGK mag wires.

battery good, cranks fast and engine spins fast and does not start.
and engine compression is good
and we test that spark is good on all 8 cylinders not just one,all 8 are test
and also tested for spark timing. for sure if distributor was removed, or set loose at base and timing lost.

if all that is good the engine now runs on spray test fuel in a can. for 3 seconds, even with fuel pump fuse pulled.
if you get this far,
we check fuel pressure next and even for bad fuel.
no history of car told
bad fuel ,old rusty tanks wreck injectors.
26 year old truck,.

things bad that old are, all fluids and belts
fuel filter packed in gunk and rust.
thermostat bad.
spark parts bad, cap/rotor wire sets x8 and spark plugs. (or timed wrong or put back wrong firing order)
injectors clogged, bad fuel or rust in the tank
bad FPR, bad map sensor.(or only clogged)
or bad fuel pump if pressure is low and FPR not bad.

most of my tests all take tools and meters
a tech can not fix cars lacking his tools.
and skills to use them./
even a timing light is needed on all distrb cars
and all EFI cars a fuel pressure gauge.
and compression gauge
and vacuum gauge.

fuses good< oops
scan the PCM see errors cranking OMG it tells you why:? sure can.
forgot the 6 new spark wire plug set, replaced 1 by one never all at once, 6 new OEM type spark plugs and gaped correctly
22 year old spark parts are no good ever.
test for spark on all 6 yet, spark is 1st or there can be no FIRE.

4.3L cranks but will not start and run and stay running.(problem1)
fire cant be seen, but spark can.
1,2,3 engine,spark, fuel good 1,2,3 in that order
spark and fuel can not run a dead engine, so 1 is first engine'
compression good 150psi up not lower, all near same
next is spark if EFI sees spark
actual fuel pressure not told just OKay. pressures matter big time in EFI, and at cranking for sure. then idle and WOT later.
engine is free running so all tests are safe, cranking too.
the service manual covers all fuel checks cranked, balance test and leak down tests.

watch scotty
https://youtu.be/064Ilsz8Fzg

not told when it last ran good, last year , 5 years ago?
that is not what any tech does, ever.
there are huge number of tests to do on car and engine both
it's not simple EFI, nor is the engine .
all fuses good
ok it does run for 2 seconds. so the engine may be good.. if it sounds good.
3 things can be bad.
bad engine
bad spark
bad fueling , is spark is detected bad the PCM cuts fuel dead by LAWs./logic and no fuel fires,.

engine compression good,? EGR not stuck open, CATS not melted./
good spark on all cylinders? ever do spark tune up
if both above are good fuel can fails
last:
FUEL bad? old and bad?
injectors leak
injectors clogged
FPR bad.
fuel pump bad:
fuel pressure not at spec, PSI


so test 1:
can you keep engine running with fast right foot at the 2seconds run?
?????????????????????????????

I would take a closer look at the fuel system and pressure - injectors are very sensitive to the correct needed values (too much or too little causes a lot of problems). I would also vertify the injectors are firing correctly - are you sure you have installed the correct ones?

That is not bad compression, you have something else wrong. IS the fuel good? What is the timing?

the coil does not crank the engine , the starter does that, sorry.
(if you ever had to hand or foot crank and engine , youd under stand that. (like motor cycles or boat engines, or per 30s cars.)

in fact will crank all day with no spark parts on car..

x2, the scan tool does tell you why there is NO STARTS, CRANKS OK. The pcm can detect, one missfire in 10 cmp;ckp signals.

• CRANK FOR 5 SECONDS
• release, key
• scan tool has DTC errors?, read the believe them.

no engine stated of 4 or more,

U checked everything but spark,
why, check spark at all cylinders, all most fire or the engine will not run or stall.
That test be first, if not starting (AFTER SCAN TEST)

IF NO spark fuses are next , not last.
lets do no start fails tests. (cranks perfectly 200 to 300 rpm)

1. : check fuses
2. key on, CEL lamp must glow, if not , ECU fuse blown.
3. crank with scan tool , see P03xx DTC errors, see RPM dead.?
4. check for spark? got spark x4 or times number of cylinders?
5. got spark try test fuel now, runs for 3 seconds?
6. yes, runs on test fuel now means lost fueling
7. no, dont run on test fuel, means, 1 to 5 done wrong above or engine compression bad.
8. bad fueling, huge number of tests. check fuel pressure now.

confused, try a shop and watch them, learn.

Three systems in engines:

Fuel delivery (fuel mixing with air to burn and making it to the spark plugs)

Ignition (lighting the fuel on fire)

Compression Building up pressure to fire the fuel
_______________________________

It is possible your engine could have low compression if it has ever been run low on coolant or oil. The engine might spin or turn over but not have fire at the spark plugs. If you are correct that the spark plugs have fire but it will not "kick" or run then fuel delivery is where I would start. See if your fuel rail has fuel in it by pressing the fuel rail valve:

If you have fuel there under a good amount of pressure see if one of the plugs smells like gas after cranking. If so the problem is not the fuel, move on.
If you don't have fuel at the Schrader valve the problem is in the fuel pump and system.
refer to a manual on how to remove the pump from the tank and replace it. This problem has signs before it goes bad. Hard starts and running rough when hot.

Good luck

You need 3 things.
Compression
Good hot blue spark to all plugs.
Good gasoline and proper fuel pressure. 13-13.5 lbs on your TBI
If you have all 3 then move on to injector pulse to both injectors.

Keep me posted and recheck your spark plug wire to make sure they are not crossed. firing order 1-2-3-4-5-6 cylinder # passenger side 1-3-5 front to back. cylinder # drivers side 2-4-6 front to back
distributor #1 is located at the 7 o"clock and rotates clock wise so next distributor post on the right working clock wise is #2. Good luck and hope this helps.

Check for spark, injector pulse, and compression.

Hi,
I don't know what year, engine etc... but I can offer an idea or two for some basics:
1. Make sure your firing order is correct.
2. Check your timing.
(If you think good, make sure your not 180 out.. in case you pulled the distributor earlier)
3. Check compression. (I've had vavles stick before)
Hope some of this helps... Good luck