Check valve after fuel pump?

[whistlinwillys]

1949 Willys
88 Tbird long block
Pimp V1.4, A237, ported head, High flow billet rail, adjustable off-rail regulator, Lucas 42lb, 380LPH fuel pump, 14 gallon fuel cell

I'm at the point where I finally ran the start up sequence in the manual.  The pressure gauge on the regulator immediately drops to zero when the pump is turned off.  My question is whether I need a check valve on the outlet of the external fuel pump?  My installation follows the attached graphic.  Second question, because it held pressure when the pump was on, I did the initial start, timing check, etc. and No. 4 is a dead hole, although the fuel pressure dropped to a fluctuating 20psi during idle (boost ref connected), which makes me think there's not enough pressure in the rail to get full actuation to the last cylinder (feed from front of rail, exit goes to APR).  Is this a valid hypothesis?

[Stinger]

Typically the pump has a checkvalve in it so when it's off, fuel can't backflow through it (at least not quickly, it will slowly bleed off over time). The regulator should function where it doesn't allow fuel past it once it's below the pre-set pressure. So when these items work this way, you've got the fuel "trapped" between the pump and regulator, maintaining pressure for a while. With that said, the engine will run fine even if pressure drops immediately after the pump turns off. Only thing it can cause is a little slower starting as it has to build pressure first (we're talking less than a second).

Base pressure (engine running but vacuum hose removed from FPR) should be around 40psi and it should drop to low to mid 30's with vacuum (not 20). So it sounds like you aren't running enough base pressure.

Neither of these have anything to do with #4 being dead. To diagnose that, first you need to see if it's a lack of spark or a lack of fuel that's making it "dead". If lack of fuel, swap the injector to a different hole and see if the problem follows the injector. If it's spark, check the wire is fully on the plug, verify plug isn't cracked, etc.

[whistlinwillys]

Thank you Stinger.  I definitely have some strange fuel system behavior going on.  I have the fuel pump on a separate toggle switch, not controlled by the ecm.  When the pump is on, the engine immediately starts dying, coughing, backfiring, etc.  If I cycle pump on for a few seconds, then off, then on, etc. I can get the engine to run, although fuel pressure decays continually.  My other observation is a large temperature difference in exhaust temp between 1 & 3 vs. 2 & 4.  Cyl 4 is averaging 150-200 degF, Cyl 2 is averaging 200-250 degF, while cylinders 1 and 3 are in the 370-450 degF range.

I did check spark at the plugs today and all tested good.  I also conducted an output test on the injectors and all test good (actuation when plugged in).  Perhaps I have a base engine issue, but it's strange how it's associated with companion cylinders.  

Also, I have ordered a -6AN check valve to put in the fuel line per your earlier comments but not sure this is a silver bullet for my issues.

I have attached my current tune (essentially the base tune plus the AFR and TPS calibration).  I have also attached the most recent log.  If you look at the voltage trace, you'll see when the fuel pump is turned on and off based on the momentary drop.  I do not currently have a FEAD belt on so the alternator is not at play.

Thank you for your assistance.

[Stinger]

If you've got fuel and spark but multiple cyl don't seem to be creating combustion, I'd suspect engine issues.

Do a compression test.

You're essentially leaning it out by toggling the fuel pump. Your wideband signal isn't working in the log though so there isn't much else I can say about that.

[whistlinwillys]

Compression Test, all plugs in placed, closed throttle body:
Cyl 1: 135psi
Cyl 2: 125psi
Cyl 3: 120psi
Cyl 4: 120psi

Cylinders 1-3 are a very rich condition, heavy sooting on plugs considering the total of 10min runtime.  Cylinder 4 plug is clean, doesn't smell of fuel.

[whistlinwillys]

As another follow-up, took a log with steady fuel pressure.  Cyl 4 still dead, Cyl 2 still cold.  My next step is pull valve cover and fix wideband issue.  Log attached below, calibration is unchanged from yesterday.

[Stinger]

You should be doing the test with all plugs out and TB wide open. With plugs in, it won't show a blown HG between two cyl as the plug in the other cyl will make it a "sealed" system.

The ECU is not capable of firing 3 of 4 injectors. It fires them in pairs so if it's not firing the injector, it's in the wiring near the injector, or the injector itself.

[whistlinwillys]

Reran compression check without plugs and WOT TB with repeatable results (+/- 3 psi).  With this being said, is there value to pulling valve cover?

[Stinger]

I can't think of any scenario where you'd have good compression but be able to see an issue in the valve cover. Anything you could see (follower fell off, bent valve, flat cam, broken spring, etc.) would result in low compression. A flat cam may be the only exception as it would likely build good compression, it would just take more cranking to get to a high value because each stroke is less efficient when the valves aren't opening as far or for as long (acts like a tiny cam).

[whistlinwillys]

Put a couple hours in today checking and rechecking with no success for firing in No. 4.  Performed injector output test again and it is actuating.  My next step on this front is to swap injector 4 and injector 3.  Installation is tight so have been putting this step off.  Rechecked spark both with spark tester as well as old school plug on manifold method.  All good.  I did find the issue on the Spartan 02 wiring and now have good wideband data.  Attaching latest log in case there is something that stands out in fueling, ignition, or settings which could be causing the extremely rough idle, stalling, and dead cylinder.

As always, thank you for your time.

[whistlinwillys]

Swapped injector 3&4, no change (followed wiring)
Swapped injector wiring harness with unmodified one, no change.

At this point I'll be looking at the main harness between the injector pass thru plug back to the ECM connector.  Assuming there is problem with the pass thru to ECM wiring, this is all ignoring the fact that any of the injectors test good when plugged into No. 4 when using the output test feature.  I've seen where high resistance can test ok in some instances but not function properly during a normal duty cycle.  I also keep considering the fact that cylinder 2 is also 75-100degF lower, although firing, vs. cylinders 1 & 3. Having swapped injectors back and forth between all four cylinders, I can say for a fact that the performance hardware is not at issue....


Log attached

[Stinger]

Note when you are doing the injector output test, it's actuating two injectors (both in that batch), so you have to make sure #4 is actually vibrating/making noise, not just that there is injector noise in general.

If you've got injectors firing in the output test in all cyl, and spark in all cyl, then wiring isn't the issue. Basically it eliminates everything from the ECU to the plug wires. It only leaves the spark plug, or a mechanical issue with that cyl.

[whistlinwillys]

Jan 6, 2023 16:15:46 GMT -5 Stinger said:

Note when you are doing the injector output test, it's actuating two injectors (both in that batch), so you have to make sure #4 is actually vibrating/making noise, not just that there is injector noise in general.

Correct... I verified this by physically touching the injector body on No. 4.  I've also tested other injectors in this harness location with no issues found.

If you've got injectors firing in the output test in all cyl, and spark in all cyl, then wiring isn't the issue. Basically it eliminates everything from the ECU to the plug wires. It only leaves the spark plug, or a mechanical issue with that cyl.

Spark plug tested for visual against ground, good strong blue spark.

I'll keep digging.  Thanks for the consideration.

[Stinger]

I can't even think of anything else to check. You've verified you have spark at the tip of the plug, verified you have fuel, swapped injectors, swapped injector harnesses, checked compression, and everything is as it should be, yet you somehow don't get combustion in one cyl.

[whistlinwillys]

Just to close this thread with resolution, there were several bugs I ended up finding.

1.) The injectors are not Lucas 42lb high impedance as the seller indicated. They appear to be Siemens 55lb low impedance 3102's (Fi-11402) per the multimeter.
2.) The injector harness I did most testing with had a wire pinched 90deg under the loom possibly causing high resistance on No. 4 lead
3.) And last, definitely worst.... No. 3 and No. 4 plug wires were switched at the distributor which probably caused 90% of my issues.

Thanks for all of the advice. I need to finish drivelines and hopefully be doing some tuning on-road in March.