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96' silverado throws code p1351

39K views 39 replies 11 participants last post by  327amc 
#1 · (Edited by Moderator)
Well, ive always had this weird problem of intermittent hard starts. Its never when cold. Only after the engines been ran for a couple minutes atleast, or fully warmed up. It cranks and cranks and I basically gotta start it like a dragster, playing with the gas crossing my fingers.

Today, took a 1mile trip to the grocery store. Truck didnt even get above 140F probably. Went to leave the store, and it was the worst hard start episode yet. And it threw a code right away. p1350.

All the other times (for years) I dont recall the p1350. But my memory sucks.

Lately, for the last 4 months or so, ive noticed this thing idles pretty bad. It is very noticable (but not as bad as stuck EGR idle). You can feel it, and it even has a distinct subtle pattern to it.
And when I smoothly try to accelerate after sitting with this rough idle for a few minutes, it gives a very small, barely noticeable shudder for about a sec or two. But once you are out of idle, it runs perfectly normal. Highway and in town cruisin is just fine. Its just sitting at an idle is the problem.

If I sit at a stop light, or in a drive up long enough, or leave it running while I go into gas station, I get P0300 (multiple misfires on several cylinders).

So I thought, well its time for a tuny. So I put on a new ICM, Coil, wires, plugs, cap and rotor. All from Performance Distributors.

No change in performance. The condition remains.

Today is when the 1350 popped up from the hard start episode.

I guess im gonna go around and clean and check all connectors. Pull some fuses and clean them as well and see what I find unless someone here has a more specific thought.

I did a search on here, and confusingly didnt find anything on p1350. :confused:
 
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#8 ·
Ive been running it for about 300miles (two weeks) now, with no issue. This is the first time I got that code. And it only happened when it did one of its hard start episodes.

I still have the stock icm that performed fine when removed. But I dont know if it is compatible with the Perf Dist screamin demon coil. ?
 
#10 ·
Ok. I read through my posts, and I think I need to sum up the history of this truck.
Pretty much since ive had this truck, it would intermittently do a hard start. You couldnt predict it.
But only after it had been started once already. For instance, once I started it, and drove 1 mile, shut it off for 6min while in store. Came out and it was hard to start. I suppose it probably got above 122F.
It has never done a hard start cold. This truck came with no engine fan, aftermarket electric fan and 160F thermostat. Will running a 160F thermostat do that?

Now recently, I noticed a crappy idle. Its not nearly as bad as a stuck EGR idle. Just a bit rough. And if I leave the truck running, while I go into a store, sometimes I will come out to a p0300 code (multiple misfires).

So, I figured I would tune her up. I installed new plugs, wires, coil, cap, rotor, and module. http://www.performancedistributors.com/vortec.htm

And not a single change in idle. And ofcourse, the hard hot starts still remain. Only this time, the hard starts are throwing a code p1351.

The only thing ive done so far is, pulled every fuse from under the hood, cleaned them and reinstalled. Pulled the plug off the crank pos sensor and inspected it. It appears clean. Plugged it in.
The next couple of days, the rough idle was approx 80% gone.

Someone mentioned to me, a crankshaft learn procedure. The engine is stock. And I did replace the cranks pos sensor when I first got the truck years ago.

I will pull the egr this weekend and fiddle with that thing. I originally though the rough idle was a slightly leaky egr. So we'll see.
I have some data somewhere on how to bypass the egr. Would bypassing the egr be a bad thing?
 
#11 ·
During the lonk cranking, do you have spark?

1) Use an air gap spark tester set at 25-30 KV and check the output from the coil wire and then at multiple spark plug wires.

I have replaced many dist cap and rotors for this code. As long as I had good spark at the coil but not out of the distributor cap.

This trouble code can set from extended cranking and is most likely not the cause of the problem as long as there is spark.

You are working on a GM truck, so don't over look the fuel pump failing.

Fuel pressure cranking should be 60-62 psi.
Fuel pressure dead head testing should be 75-100 psi.


This is using specs for a 5.7 V8 Vin R

Steve
 
#12 ·
Thanks for the info steve.

This is my 3rds set of caps and rotors with no change. First set was stock. I dont recall this rough idle with the old stock cap, but the reason I changed it was a nasty misfire on #4 on the way home. So it was def toast. 2nd and 3rd set was Perf Dist. There has been zero change swapping them two out.
Are there any components on the distributor? Capacitors?

A friend at work did mention fuelpump. And I have had a similar problem on my jeep. The terminal in the fuel tank was loose, had bad connection. So once it heated up (you were down the road) it might die. If you shut it off, you DEFINITELY couldnt get it started, cause too much resistance/heat has built up in that plug.

My fuel pump is OLD. So I will go after it this weekend. Figures. I have a full tank of gas. I will check pressures first.
 
#13 ·
Just another suggestion, the "fuel injectors" or poppets are notoriously problematic on these engines!!! They will leak fuel, stick and not supply fuel, get dirty and not atomize fuel....and the list goes on.

If your ignition components are known to be good, and fuel president is within spec, don't rule it out!

Also don't replace them with the same problematic factory parts. Google Vortec MPFI conversion. I believe they are made by Delphi! I will look for my empty bod or a part number for ya.

Just something else to check!
 
#14 ·
The conversion is made by Delphi. The Delphi number is FJ 10566. The benefits are easier starting, better power and economy due to better atomization and fuel metering. Also the factory poppets only flow 19 lbs. an hour. The aftermarket injectors I thought were 21 or 22 lbs /hr. Nice to compliment to any future upgrades.

Food for thought!
 
#15 ·
Thank you for that info CJ. I do have an extra set of factory injectors layin around. But I will not use them as you suggested. Does the higher flow rate of the Delphis cause check engine light? Since they are out of spec, didnt know if the computer would get pissy.


I just took a 100mile drive today. On the (cold) start up for the drive back, it idles for a few seconds, and then check engine like came on, flashed for a minute, and then stayed on for the whole drive home. P0305. Misfire on 5.
This is just getting damn crazy. The cap and rotor is brand new. The rest of the ignition is only 2weeks older than the cap and rotor.
Its worth noting that the 'misfire' wasnt detectable at all by me. And I was paying close attention. I have had a bad cap give me a #4 misfire that was just god aweful. Just fyi.

Would malfunctioning injectors cause the computer to detect or imagine a 'misfire'?
Would the computer see a weak cylinder and label it as a 'misfire'?
 
#16 ·
The MPFI and the stopck poppets flow exactly the same. It is not a performance enhancement so far as maximum fuel flow is concerned.

Both the MPFI conversion spider and teh stock spider flow at 2.012 gram/second or 23.1 lb/hour.

You would only notice the difference from the new MPFI conversion spider is if the stock poppet spider is malfunctioning.

Some info
http://members.shaw.ca/betterthanyoutoo/Sticking Poppet.htm

A missfire is an "odd" acceleration or deceleration of teh crank which is detected via teh crank position sensor (CKP).


these engines are notorious for eating distributer gears. Signs of this a chugging when cruising, made worse by the A/C compressir bveing engaged. Just remember that in tehse trucks you dont have to have teh a/c button pressed for the compressor to be running. If the air selector is 3 or more "clicks" clockwise of the 12:00 oclock position, your compressor will be running irregardless of teh a/c button.
Fuel pressure should be 60-66 psi Key on engine off, and should be slightly lower when running as the FPR will bring the pressure down in response to engine vacuum. A quick jab of the throttle should cause pressure to spike on a running engine. If pressure doesnt change, suspect an FPR. Located on the actual fuel/poppet supply block insid ethe intake manifold/plenum.

If you have anothers et of popet/spiders I would try them as you only have to take the upper intake off.

peace
Hog
 
#17 ·
The computer controls how much fuel goes in the engine. The higher flow will only be used if it is required. The computers on these engines will adapt to changing parameters to an extent. For an example, I have a 1996 3/4ton with a 383 stroker fueled by the factory intake and injection. The only problem I have is on really cold Wisconsin days, the slight knock from the forged pistons on a cold start-up sometimes trip the knock sensor, and there by retarding the timing. Only hapens when its below freezing and only for a few minuets!

Any other questions just ask.
 
#18 · (Edited)
Totally awesome info guys. :) Thats totally awesome that the comp will accommodate a 383! :drunk:

I removed the A/C compressor a few years ago.

I dont have a 'chugging' when cruising, or at all really. So I hopefully can rule out dist gear. But I do have an extra melonized gear layin around incase.

If this dog will make it one more week, I will swap the injectors next weekend. Assuming the fuel pressure checks out ok in the mornin.

Is there an online manual for this turd? 96' K1500
 
#22 ·
327amc said:
Totally awesome info guys. :) Thats totally awesome that the comp will accommodate a 383! :drunk:

I removed the A/C compressor a few years ago.

I dont have a 'chugging' when cruising, or at all really. So I hopefully can rule out dist gear. But I do have an extra melonized gear layin around incase.

If this dog will make it one more week, I will swap the injectors next weekend. Assuming the fuel pressure checks out ok in the mornin.

Is there an online manual for this turd? 96' K1500
The PCM will accomodate any engine so long as its tuned for it. The engine will run fine during closed loop as the O2 sensors provide feedback for part throttle fueling but as soon as you go to WOT the PCM only fuels what it is programmed to fuel. For max performance, the PCM will need to be tuned for anything other than stock.
GM sells a complete 383 kit for these engines that will RUN with the stock tune, but even the GM literature states that for optimized performance,PCM tuning needss to be done.

If you want the best info for the Vortec 305/350, the PPE trucks ite is where its at. This is where the marine intake and 411 PCM swap originated. Good info, no childishness like with other truck forums.

The PPE forums
http://www.pacificp.com/forum/index.php?sid=386b9c35032f82c063e805d5d626670f

Marine intake swap
http://www.pacificp.com/forum/viewtopic.php?t=317

411 PCM swap
http://www.pacificp.com/forum/viewtopic.php?t=3240

Just to warn you, the melonized gear that the Vortec 4.3/305/454 1996-2002 engines run has a unique shaft diameter that only the Vortec distributers have. I wanna say 0.429" but cant remember 100%.

peace
Hog
 
#23 ·
Ok. I have some more info.

I basically refuse to just swap parts until the problem goes away. Im so tired of doing that with this turd. So I decided I would check obvious things and just keep driving until I get an all out failure, or more codes. Bout a month ago i idled the truck in the driveway, cleared all codes, and shook every wire on the ignition and crank pos sensor. No stumble or codes. So that went well.
Over the 4th holiday, I didnt drive the truck for 5 straight days. On the 6th day when I went to start her, she hard started, sputtered, and died. But then started on the 2nd crank. Thats the only time ive had a hard start when she's dead cold.

Well, yesterday, I got 4 codes on the way to work. They only happened sitting at a stop light.

Ofcourse there was the '1351' code. And there was 'misfire on #5 detected' and 'bank 1 running rich' and 'bank 2 running rich'.

Now, the 1351 is pretty common place anymore. It will go on and off on its own through out my drive cycles. The only other code Ive got (about 2months ago) was a 'misfire on #5 detected' which now makes the 2nd time ive gotten that code, even though everypart of the ignition is new. That plug looks great. I could swap it with another...
Not to mention, the exhaust is noticeably richer to the discerning nose.
So I think things are starting to add up. Im leaning toward injectors.
Especially after reading these reviews. http://www.amazon.com/Delphi-FJ10566-Fuel-Injector/dp/B000TYLIFS

But how can faulty injectors cause a 1351 code (Ignition Coil Control Circuit High Voltage)?

Im gonna start taking a different route to work that doesnt require constant stop lights. Idling seems to really be the major catalyst in getting codes to pop up.

Thanks again for all ya'll help so far. We aint there yet.
 
#25 ·
there are a couple of very common problems with this engine that haven't been mentioned.
one is a leaking fuel pressure regulator. it can cause hard starts when the motor is warm and has been off for just a few minutes.
you can check the regulator by pulling the air duct off and locking the throttle plate open. then without cranking the motor, turn the key on for a couple of seconds and then back off and wait for just over 10 seconds and repeat 3~4 times. now put your nose into the opening and take a good sniff.
if you smell raw gas, you have a leak.
you can also use a flashlight and a mirror to see the regulator with the throttle plate locked open. the regulator is toward the back of the motor.
anytime i had an upper intake off, even if it showed no signs of leaking i always replaced the regulator unless it had been recently replaced.
i've seen extended cranking caused by leaking regulators set code p1351.
as the regulator leak gets worse it will set rich codes, and if leaking bad enough, cause misfire codes.

next, the lower intake gaskets are a major cause of misfire at idle.
normally it starts out as a cold start misfire lasting just a few seconds that quickly goes away as the motor warms up.
as time goes by the misfire lasts for a longer amount of time and gets progressively worse.

if you do replace the lower intake gaskets, get the metal Fel-Pros as the plastic on the factory gaskets is what fails.


i'll also mention GM sells an additive designed for the poppet injectors that i have used to clear up misfires caused by problems with the poppets.
 
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