I have a 98 GMC serria 350 Vortec I had engine rebuilt. I didn't have a misfire before I had it rebuilt but now I do. I replaced ICM ,Coil , Pickup coil ,sparkplugs, sparkplug wires, cap & rotor had it put in time by a shop. It misses worse when the engine gets to normal temp.When I first start it up you can't even notice a miss. And I get a P0300 Random Misfire Detected. Does anyone have any ideas please help me.

not told is engine misfiring still,? (besides DTC errors)

1996, 350V8 engine, 5.7L new name today.
C1500 right with C in front? not K1500>?
VIN R coded Automatic trans.
1351 (no front letter told) why post DTC lacking full and complete DTC????
answering for USA spec, cars only me.
i get only 1 hit

Trouble Code: P1351 (5.7L V8 VIN R Auto)
ICM Ignition Control Circuit High Input so after replacing the part
we reset all DTC errors using the scan tool (a button on it)
and drive and see if it comes back or otere pop up.
if does p1351 again,
the wiring is bad to it.
the SM states this

• ICM control circuit is open, shorted to ground or shorted to B+
• ICM power circuit is open (check power from the ECM1 fuse)
• ICM is damaged or has failed
• PCM has failed

bad grounds to all that.
the ICM step 4 in the manual told you the ICM must be mounted
not just nakked(sic) ever but with thermal compound.
like seen on computers today,(called heat sink grease (SLANG)
MUST, OR IT OVERHEATS, FOR SURE, LIKE CLOCK WORK
BEST IS NEW DISTRIBUTOR THIS OLD. IMO
AND ALL Wiring to to it clean and tight , no rust or bad connections.
even loose fuse or one that is damaged, ENG1 and ECU1.


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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)

Have you run a fault code test? do that it is easy no special tool needed other than a paper clip. Watch the video. Reading OBD 1 Codes on GM 1982 1995

Replace the pickup coil in the distributor this is where you get your pulse for the injectors.

Do you have spark at the plug end of the plug wires?Have you double checked the firing order is correct? If you are sure it is correct 1,8,4,3,6,5,7,2 ,then you will need to check the ignition timing,if that seems good then you may have to get into it a little and check the cam /valve timing..Hope this helps !

I take it,you replaced the crankshaft sensor,now,the cam sensor(pick up coil)is most likely the problem,it is either not lining up,or,there is wear in the distributor.The crankshaft sensor is not aligning with the cam sensor(pick up coil).

PO 1361 ignition control circuit low voltage. Check your ignition module and coil.

Check the wire harness to the Ignition control module (ICM) or replace it. It cost around $40,00 from Auto Zone and it's common for the ICM to fail, or it may just be starting to fail and it's also know that the OEM distributor had a screen vent at the bottom of the distributor for ventilation to prevent condensation from forming in the distributor. Check to make sure your new distributor has a vent and that it's not plugged up with shipping plastic. Condensation may be forming causing the misfire in the distributor. Good luck and keep me posted. 

Did you try typing in your number off the dash into the machine for the codes. Mine didnt give me any either until I typed in the dash number.

hi there, if you can feel the misfire at an idle but not at a higher rpm than the fuel pressure regulator is bad im working on one right now that has mifire code and random misfire codes coming up