# 96 Chevy Blazer 4.3 codes p1351



## Marine76

Have to crank engine for a long time for it to finally start. Then it codes p1351 (Ignition coil high voltage). This is an intermittent problem. Most times it starts just fine. Could the ICM be the problem? Has anyone else had the same problem?


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## partzkarz

yes distributor rotor or coil wire is corroded look close


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## Marine76

Thanks partzkarz, I'll check them tomorrow, maybe it will be such a simple fix.


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## wolfen1086

Clean all the connectors and replace he cap and rotor, if you have a multimeter handy check the voltage going into and out of the coil, if its out of range replace it.


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## Marine76

Cap, rotor, coil and ICM replaced with no success. Problem still exists. Any suggestions?:banghead::facepalm:


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## wolfen1086

Do you have a code reader that clears codes?
if you do clear them and try starting and see if the code comes back, if it does after replacing those parts its something either in the computer system or the wiring would be my next bet.


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## Marine76

Already cleared codes twice, will try to check wiring tomorrow.


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## wolfen1086

Also check the sensors, on some Chevy's a bad sensor can ruin the whole day.


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## Marine76

:dance:Today I bought a used computer and installed it. Of course it coded for the same problem dtc p1351. After looking at a wiring diagram and checking various grounds the problem continued. Next I changed the crank sensor, cleared the codes and so far it hasn't coded and is running fine. (knock on wood!!!!)


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## wolfen1086

Good job Marine

Save that computer, trust me as long as you have a spare you'll never need one


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## s10fan

I just wanted to give my experience with P1351 in hopes that someone may benefit.
I've owned 6 s10 rigs from 1988 through 1998 and between my kids and I we are still running 4 with no less than 200K miles on any one of the rigs. So, I believe in the product.
My personal rig is a 1995 ZR2 OBD2 (more like 1 1/2) that I purchased from a gentleman that was very anxious to rid of himself of the rig. I drove it for a couple of months then out of the blue it just quit running at low RPM's. With enough key cycles it would restart and continue running for one trip, a whole day, a week or whatever then fail again. After several of these I found a code reader that worked on the 1 1/2 version, an ENNOVA 3100a. The code that came up every time the rig wouldn't start or every time the rig would just quit at low RPM's was P1351 and no other code.
First I noticed the previous owner had cut up the wire harnesses and replaced the coil, cap, wires, cam position sensor, ignition module, and crank position senor (obviously why I got it cheap). I verified fuel pressure engine off, engine on and engine under load, no problem. Preformed the fault tree in the service manual and every time I came up with a timing voltage of 5.8Vac, should be 1 to 4Vac. I changed the VCM with another that I had on hand still 5.8Vac. Don't jump to the VCM even if the flow chart would have you change it. It's probably not the problem. I did notice that every time the unit crapped out it was at low RPM's and the tach would just drop to 0 even with engine still turning over and during cranking the tach would remain at 0 until the magic key cycle that started the rig, the tach would jump up to an appropriate value for idle. One cold day in 3ft of snow I had a hard failure, it would not restart with 8, 9, 10 key cycle attempts. With the tach issue and P1351 I had been zeroing in on the crank position sensor (CKP). Sure enough the previous owner had changed it with an aftermarket unit that didn't have the shims (1995 shim issue) so the CKP was hitting the reluctor on the crank and truly had failed (cut it open and verified failure). With a brand new CKP the rig lasted about a week then the problem reoccurred. Verified P1351 and even the tach dropped to 0. Further study of the service manual lead me to fact that with key in the ON position the VCM needs a signal from the CKP even if the engine is not rotating. I turned the key on, vigeriousely wiggled the manipulated the wire harness from the VCM to the CKP and sure enough when I manipulated the connector at the CKP the relay that powers the fuel pump tipped in and out. I disconnected the CKP and did a pin retention test (just stuck a pin from an old O2 sensor into each socket) and it just fell into one of the sockets with no retention resistance. Upon examination the little leaf spring was completely flat. With a dental pick I was able to reshape the leaf spring in the socket and one problem solved. From then on the P1351 failure was not accompanied with a tach reading of 0. As long as the engine was rotating I got tach.
I discovered that if I erased the P1351 code the rig magically started. So, I kept my code reader harness permanently plugged into the DLC and reset the code whenever the P1351 occurred. Like magic it would start. This went on for a long time until just the other day I couldn't get it started and every attempt resulted in a P1351. I verified spark, so I fed a little gas through the PVC port on the intake and fired right up. I found that if I could get the RPM's above 2500 on the gas that I was feeding the the rig It would magically keep running.
I took out my service manual one last time, fix it or throw it away. The first block on the flow chart for P1351 was "disconnect the fuel injector(s) and crank the engine for 30sec. then verify that the unit threw a P1351". Like a bolt of lightening I connected the fact that without feedback on the injector circuit the VCM will throw P1351. This not explained in the manual. I disconnected the fuel injector (1995 only has one) and sure enough both sockets had no retention on the pins. The little leaf springs were completely flat. Disconnected all sensor connectors including the ABS (I was having an intermittent on it as well) and found some suspect sockets, fixed them all and sure enough the rig runs better that it has ever.
I then observed that when disconnecting any of the gm weather proof connectors the socket side will snap over away from the pin side because of the force required to disengage the locking element. Upon further observation the pins are slightly engaged into the sockets when this happens. Therefore, the probability of socket damage when disconnecting a gm weather proof connector is almost 100%.
Conclusion: If you are getting a P1351, check the sockets for pin retention on the crank position sensor, cam position sensor, ignition module, and injector(s). It will only take a few minutes and if these connectors have been disturbed the probability is high they are damaged.


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