ILYA

Troubleshooting a Vortec 7400 (MPFI 454) in a 1996 Fleetwood Bounder 34-foot RV. Purchased at an auction, in a very nice condition overall and only 90K miles, with a recently rebuilt O/D tranny and engine problems. Unclear how long the RV has been in-operable. May have been sitting for a long time potentially. I purchased it in May of 2016, tinkered with simple sings, then it sat for exactly 3 years until I started poking around again just now.

When purchased in 2016, the engine was knocking, smoking, shacking, and ran very rough. It was driven from the auction for a mile or two. The engine turned over, wanted to start, smoked out of exhaust, shook violently, may have started and idled for a few seconds, giving it throttle didn’t seem to change anything, it just choked at low rpm and died pretty quick. Then it quit starting at all.

I’ve checked the distributor at #1 TDC, new cap and rotor, didn’t observe any rotor “side to side” play. I’ve installed a new PCV, new fuel filter, new air filter, new spark plugs are now NGK Platinum, new coil, etc. Then I gave up trying to fix it on the side of the road and towed it home, where it sat for 3 years since, now I’m starting to troubleshoot again…

So I’ve charged up all batteries and gave it another shot last weekend. Drained the oil, it has some gasoline smell to it, no metal chunks. Same symptoms as above. Turns over, bumps and grinds, but not starting. CEL is on and it has something to do with code P1351 - that's the ONLY code that comes back after I clear them - started a diagnostic procedure found online. One of the first steps says to disconnect the injection pump harness - clear the code and try again - the code does NOT come back with the harness disconnected. Troubleshooting guide says to “check other diagnostic aides”. What does that mean?

I know that 2 items of concern with the Vortec 454 engine are #1 the injectors and FPR and #2 the distributor bottom gear shearing, these big block MPFI motors are better than CSFI ones of smaller displacement, but still have issues. Since the timing was just right when I put it on #1 TDC, I am guessing that spider injection is more likely to be the problem, either FPR or Injectors (might as well replace them all). Does it sound more likely the injection components need replaced if code P1351 does not get set with injection harness disconnected? Or could the lack of code be caused by something else? Could it be a short in one of the wiring harnesses or is it more likely a dead short in the injector circuit (due to a bad injector)?

Here's a video of the engine turning over with the injection harness connected - throws code 1351 –
Here's a video of the engine turning over with the injection harness disconnected - no code 1351 -

73shark

Welcome to the forum. You need three things, air, fuel, and spark. Pretty sure you're probably getting air and if your timing light had an inductive pickup then you're probably getting spark. I would try spraying a small amount of gas in the throttle body while somebody else is cranking it over to see if it'll start.

ILYA

Tried spraying starting fluid into the intake when initially troubleshooting and had no start. I am also guessing I have the spark, question is if it's timed right, I was about to pull the distributor to check the bottom gear for wear when I ran into that code 1351. Thing is, when at TDC, the distributor rotor is correct, so I'm starting to doubt it's the distributor related. New coil and spark plugs. The only other thing related to spark might be the ICM, I would have tested it, but got stuck on that code P1351 disappearing when I unplug the injection harness. That discovery got me off the ignition-related track. These MPFI motors have a better fuel system than CSFI Vortec's of smaller displacement. But FPRs do go bad on big blocks and fuel injectors do leak on these too. I wonder how likely is it that these issues may be related to fuel delivery?

73shark

Does it have a HEI type of distributor? If so, maybe the module is bad. If it doesn't fire with ether then maybe no spark.

ILYA

Found this PDF by googling and it lays out the entire P1351 testing procedure:
https://f01.justanswer.com/Bluegoril...document-8.pdf

And the part that I was missing from other online sources - "Diagnostic Aids" (when code disappears with injectors unplugged)

A poor connection, a rubbed through wire in the insulation, or a wire broken inside the insulation will cause an intermittent.

Check for the following conditions:

(1) Poor connection

(2) Damaged harness: Inspect the VCM harness connectors for the following conditions:
- Backed out terminal C3 pin 9
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- A poor terminal to wire connection and
- Damage to the harness.

(3) Intermittent test - If the connections and the harness check OK, monitor a digital voltmeter connected between VCM connector C3 pin 9 and C4 pin 18 while moving related connectors and wiring harness. If the failure is induced, the voltage reading will change. This may help to isolate the location of the malfunction.