1996 gmc jimmy wont start seems like advanced timing issue backfiring out throttlebody, replaced timing pick up, distribitor cap, crank sensor, ICM, when ignition conrol module replace the engine ran fine for about 4 seconds and went to backfiring out throttlebody, then replaced injectors inside intake manifold, still backfiring. it has 65 psi fuel pressure. this whole problem started after wife drove car it quit and had to tow home. distribitor is tight. i have not checked with a timing light. it is late and didnt think to check with timing light until right now. any ideas ?

step one is test spark at coil first not distributor.(last)
the coil has a HV lug use spark wires HV + plug to test that this is first. if fails the distrib is bad, VR pick up.
s15 jimmy or PU
which engine,
2.5L 151cid L4
2.8L 173cid V6
4.3L 262cid V6 <<<< I will guess this and answer.

try new distributor.
and must be timed,
set engine, to TDC 0-degrees, #1 piston on firing stroke
step1 is that. so new dizzy super easy to put back same. time.

the ICM runs the coil but the ICM has inputs, that must be working
1988 uses what to make ICM work, good pickup coil
The PCM (VCM) runs the 4 wires to the Distributor and ICM in it.
if PCM is bad, or inputs to it are bad, there will be no spark
there is no CKP sensor here ,just CMP and CMP is the pickup coil inside DIZZy and connect to ICM and ICM makes spark. (ign coil)
the PCM I think only does spark timing advance.(called EST)
but no sure me how the 4 wires on PCM to Dizzy work.
a new pickup coil might fix this , (it is CMP named now)
CMP is cam sensor and here it is via cam to main DIZZy shaft to pickup coil)

Crankshaft sensor.

Remove number, one spark plug , turn engine over till compression is felt, turn engine over till TDC marks on crank pulley and timing cover marks line up, fit distributor to motor with rotor pointing to number one distributor cap tower, start and set final timing with timing light.

This just happened to my Dad's 1998 GMC Safari...

Firstly...

Check the hard vacuum line as previously noted by others.
If that's ok, then take off the intake pipe and spray brake clean into the throttle body while trying to crank it.

If it starts.. then you have a fuel related issue, if it doesn't start then you have an electrical related issue.

Our van did not start after trying to use brake clean.

Take off the console inside the vehicle's cab and get at the distributor.

Usually people noted that the ICM (ignition control module, inside the distributor) was the main issue here, but on our van, the distributor and wires looked brand new so it was probably recently changed (we got this van 5 months ago), so I assumed the spark plugs were also changed at the same time.

We unplugged the connection from the coil to the distributor, tried to crank it, and no spark was being generated, boom, got a new coil and starts up fine.

Just takes a bit of trial and error.

check the firing order of the HT leads as it is easy to cross 2 leads
the timing is set at 12 degrees btdc and no where else so use a timing light and set it there

I would check for a spark first, but you can pull of the distributor cap and check if the rotor is still turning. If it is not turning, you may have a broken timing chain. If it is turning and there is no spark, it is probably bad spark plug wires, spark plugs, distributor cap, rotor, camshaft position sensor, or crankshaft position sensor.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

check the igniton module in the distributor also check the rotor bug and cap and one other thing check the gray! impluse feed wire from the fuel pump relay all the way down through the frame back to the fuel pump inche by inch! in 1997 GMC and Chev had issues with faulty wiring in the fuel pump feed harness and i found over 700 trucks would lose voltage in the GRAY wire somewhere in the frame and usually in a section under the cab and front of the bed area the wire wont be broke visably! it breaks internally making it hard to locate visually you will need a test light or a volt meter to trace it down

If it jumped time it may backfire and run poor but not miss.
Check coils and wiring.

you are off the timing by a tooth or two. when you replaced the cap and rotor, if you did not mark the position of the rotor with some point on the motor or firewall, then it is likely that you installed the rotor by a couple of degrees. so, when you are going up hill, and the engine needs to advance the timing to add power you timing is off even more causing lack of power and sputtering and backfiring.

fuel pump maybe