5.7GI-300-J: left side cylinders not firing- ignition issue???

chim chim

Cadet
Joined
Jun 10, 2021
Messages
7
Hi all,

Sorry for the lengthy post but it covers a lot. I have a 5.7GI-300-J (2008 with EGC computer, 300 hrs) that has been running horribly since putting in the water this spring. Last year it was running perfect after new fuel pump/filter/pressure reg. and distributor cap/rotor. Winterized it and then put back into water in April. This spring did some other routine maintenance including taking exhaust risers/manifolds off to check for clogs or riser thinning, as well as changing raw water pump and some pulleys that were corroded. Getting a mechanic to look at it is taking weeks so I tried to resolve myself.

Symptoms: running rich (strong smell of gas in exhaust), rough/unstable/low idle, plugs fouled with soot (especially on left side cylinders 1-3-5-7), low power when driving, left side exhaust riser doesn't get hot unless really revved (unlike right side), and even then only warm

During troubleshooting, I recognized that I could pull injector connectors or plug wires off any of the left side cylinders and it wouldn't affect the poor idle. In contrast, doing so on the right side cylinders would cause worse idle and lower speed. Clearly the left side is not really firing.

What I have done after searching online based on symptoms:
  • checked wiring and connections incl. sensors for any breakage or disconnects
  • fed a container of new gas into the fuel pump to make sure it's not gas quality/water. Also dumped out fuel filter and no water seen.
  • measured or verified for correct fuel pressure and no leakdown, correct plug wire order, signal present at each injector using noid light, spark at each cylinder, ok cylinder compression (all similar about 160)
  • verified no fuel leaking from fuel pump vent chamber to manifold (heard this could cause rich running
  • verified left side plugs are heavily sooted but not wet
  • changed ignition coil/module, IAC, MAP/T, plug wires, and changed dist cap again
  • had fuel injectors tested and ultrasonically cleaned (all were at spec before and after cleaning)
None of this helped. I then got the Diacom software to see if any codes were showing as well as to get other diagnostic info. No codes showing. I ran the spark kill/injector kill tests and similar observation as before: left side cylinders no impact, right side causes lower speed. I could post the Diacom report if it might help.

Root cause seems to be left side not getting correct spark/fuel timing. At this point, I suspect could be a computer problem (injector pulse width or spark firing at wrong times?) As it is EGC, I can't get a reman'd one easily so swapping/replacing it is last resort.

Or maybe issue with distributor. I have read many threads that these flat top distributors have critical alignment issues but not sure if that would cause these symptoms.

Diacom software says cam retard is 11.5* to 12.5*. Does anyone know what is correct number? I only have engine manual for engines through 5.7GI-E, and it states Ignition timing is 10* BTDC. Is this same as cam retard reported by Diacom? It also says spark advance goes from 10* to 30* as I rev from 1200rpm to 3000rpm.

I am at my wit's end. Any thoughts or suggestions? Thanks!
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
34,872
welcome aboard.

your motor has a distributor, and with the firing order, there is no way that only one bank can not fire. That can only happen with a COP engine (coil on plug)

cam retard and ignition timing are two different things.

when was the last time you had the injectors cleaned?
 

chim chim

Cadet
Joined
Jun 10, 2021
Messages
7
Thanks. I agree it makes no sense that only left bank doesn't fire. Given that there is spark and lots of soot on the left side plugs it seems it is trying to fire, but something is preventing it. As mentioned I can pull all the left side plug wires off or the left side injector connections and no impact to engine speed, which implies that those 4 cylinders aren't producing power.

Agree that timing and cam retard are different (just learned that!) and that the ECM controls the timing so it's not adjustable. I don't know what the correct cam value is, so the value of 12* reported by Diacom might not be correct, but it might also not be the problem.

I had the injectors sent out for cleaning/testing just last month, after the problem started, in hopes to fix it. No luck. All were at the rated flow with good spray pattern.
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
34,872
Im going with stuck injectors or dirty injectors on the one side. If you check fuel pressure, then key off, does the preasure remain, or drop immediately?
 

chim chim

Cadet
Joined
Jun 10, 2021
Messages
7
It this a multi-port injected engine? Could be an injector wiring issue . . .
Yes, it's MPI. I guess it could be a wiring issue, but I did check the connectors using a noid light and they all seem to pulse similarly when cranked- right side same as left side.
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
29,531
You sure its not in S.L.O.W mode? Thought that turned off half the injectors when it got into that mode. Rinda Diacom should certainly show if you are in that mode or not.
 

chim chim

Cadet
Joined
Jun 10, 2021
Messages
7
You sure its not in S.L.O.W mode? Thought that turned off half the injectors when it got into that mode. Rinda Diacom should certainly show if you are in that mode or not.
Thanks, but Nope, its not in slow mode. Diacom says the engine derate is off, and there are no codes. I can rev it to 3000rpm but still runs rough at those higher rpm.
 

chim chim

Cadet
Joined
Jun 10, 2021
Messages
7
I attached a Diacom output for fast-to-slow idle. The injector pulse width confuses me- I don't really know what the pulse width reflects, but I would have thought that the pulse width should get smaller at lower rpm.

Anybody know why it pulses to higher numbers and is this expected?
 

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