My FI Frustrations Continue, Still have engine cutting out Options

[dralf]

I keep purchasing components for my 1975 D Jet system but to no avail in solving the mystery of why it will sometimes cut out when the reves are about 2500 and the engine is under load. For those who have read my earlier posts, I now have new wiring harness, coil, points, condenser, cleaned the dizzy, new Auxiliary Air Valve, and cleaned all wire connections. Also replaced the fuel filter. My recent purchase was a new MPS for mine had a diaphragm leak. I drove around the block and was happy for the first lap since my adjusting the valves and timing seemed to improve acceleration. Unfortunately by my second lap the engine started to randomly cut out as it have before. My path forward is to replace the vacuum advance diaphragm on the dizzy which I found a leak. also to check the cylinder head temperature sensor, and the throttle position sensor. I there anything else I should be checking or replacing ? I am thinking about setting up my timing light inside the cabin so I can verify that during those times where the engine cuts out the spark plugs are still getting power. I hate to think my ECU is bad. Also where or who can check that out if it comes to that ?

[BeatNavy]

With FI it's helpful to broadly define the issue (e.g., fuel delivery or ignition) and then narrow it down to root cause (which you are doing, good)., So, you can:

1. Buy a Harbor Freight fuel pressure gauge kit. Attach it to the little port of the 1/2 cylinder fuel rail. Verify ~29 or 30 psi and relatively steady (it may shake around some, but shouldn't drop or spike significantly).

2. If you need to adjust pressure, follow that fuel rail line toward the back of the car and you'll find the fuel pressure regulator. Unlock the lock nut (13 mm wrench) and adjust the 10 mm nut (clockwise, or tighter, to increase pressure, opposite to reduce). Tighten up the lock nut.

3. Make sure your FI grounds are clean and connected solidly to the multi-ground point. If those are loose, they will shake during driving and cause symptoms like you are describing.

4. Check all connections at relay board, particularly fuel pump relay and 4-pin connector. Make sure they are clean and seated snugly.

5. Make sure all FI connectors off wiring harness are snug in the injector.

6. Inspect wiring harness for shorts and other issues, particularly to injectors, grounds, and CHT.

7. Test your injectors using the baby-jar flow test. Even better, send them to Mr. Injector for cleaning and flow testing. Less than a week and $17.50 per injector eliminates major unknown.

8. If you get other signs that fuel pump is actually the cause (possible, but not first thing I'd assume), buy the Bosch 2-port and go from there.

Good luck.

[mzalanka]

Everything BN said. You can also get a HF noid light for about $40 to make sure the injectors are seeing a pulse after the engine cuts out.

Something I've noticed with my car - which has a permanent inline fuel pressure gauge - FP is always 4 to 6 psi higher cold as opposed to fully warmed up. I have mine dialed in so that it is about 36 cold, and 30-32 warm. I am interested in other's opinions but I have chalked it up to increased resistance in the wiring to the pump when the engine is warm. I have the pump in the frunk so there's a lot of wiring for the electrons to push through.

If I dial it to 30 cold, it runs really poorly warmed up. It's possible your FP is normal cold but drops when the car warms up, and can't keep up with demand under load.

I also had a problem where I had a kink in my return line and my FP was pegged over 100. Never would have figured that out without the inline gauge. I highly recommend installing one as it will help immensely - and for years to come - with troubleshooting.

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