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 ?

My bucking or cutting out I found was related to 2 things.
1. TPS board worn
2. Somehow the distributor- once I put the 123ignition distributor in it went away completely. - this eliminates the points on top and the FI points.

If you haven’t checked the TPS, go there next and if you have, then it could still be something with distributor or points. My bet is the TPS- have not seen the other thread so if this has been done then NVM

I second verifying/replacing the TPS or just it’s circuit board.

Also second your thought to replace the vacuum advance. Very HTF. Just get a 123 dizzy if a good vac advance cannot be had.

Also lube the advance weights if not done recently.

Seriously doubt it’s the ECU.

I missed your other post on the subject.

I would double check your dwell and timing. Set dwell first, then timing.

Like others have said - the TPS board is your most likely suspect. Install a new one and calibrate it properly.

Verify that the CHT is tight and properly seated in its mounting hole.

Also, have you checked fuel pressure?

I've aslo experienced missing due to oily trigger points.

Keep fighting through this - it's worth it.

I had an instance a few years back where I was out driving and my engine would randomly cut out and it eventually stopped running on me. Luckily was able to get it restarted and almost home when it died completely. I called my brother and we got it pushed the few blocks back to my house where it dawned on me to double check the fuel pump fuse on the relay board. It was vibrating loose randomly and had come unseated
enough to shut down fuel and stop the engine. Not sure it's what you have going on or not but you don't mention checking your relay board so give it a look and make sure nothing is suspect there. I've also had weird missing/cutting out because I had a bad
connection on my CHT sensor.....
Also, if you haven't already, check that the harness ground connectors are secure on the 3 terminal connector on the engine block.

Thank everyone for tips and things to look at so far ... yes I have cleaned connections and replaced the relays to insure they were 100% good.... will focus on the throttle position sensor and perhaps get a 123ignition distributor once I find who sells them.

Odd things to check - replace any wires in ignition system, have had a couple internally broken wires from the distributor to the coil. 3 x in 40 years. 2 of the breaks were where the internal wire went thru the body of distributor. it's the original wires that aren't usually replaced. Try a loaner distributor

Related to Post #5 above...more than once I've seen posts related to relay plate and harness connector problems. I experienced that myself, had the car simply shutting off at random times (fuel pump cutting off).

Remove the wiring harness connectors and carefully use a razor blade to slightly bend open the male quarter-sliced electrical pins. Clean them all off and lube with dielectric grease.

Same goes with the quarter-sliced male pins on the relays themselves.

Reinstall, fingers crossed.

FYI 123 Ignition distributor COMPLETELY solved my random stall issue.

Stock distributor had too much axial play. Compufire electronic ignition was also going bad.

I balked at the cost but I had isolated it to the dizzy and it was a plug-n-play solution for me. The car runs great now.

A better solution for cleaning/protecting terminals in an engine bay is DeOxit. Its a solvent based cleaner and yet it has other additives that protect against corrosion and does not attract dirt like the dielectric crease does.

Dralf, I once had a similar symptom with my 76 where it would cut out intermittently under load with revs between 2000 and 2500. A P mechanic at the time diagnosed the problem by disconnecting and grounding the CHT sensor lead (engine warm) and it ran fine, so we replaced the CHT sensor and that solved the problem.

If your into vintage stereo and electronics, you know this product.

After I redid my system I experienced similar sudden cutout. One of the the connectors from new harness was not seated properly. Once i found that, all good. Recheck every connector and make sure properly attached.

I have a new bit of data for my intermittent runnability problem. Today I attached my timing light to one of the plug leads and put the light on the passenger seat. I then drove around the block numerous times until the engine cut out the sputtered and then the engine kicked on with a bit of a jerk. I was watching the timing light during a few of these incidents. Each time the timing light was flashing which told me that the engine was getting sparks thus the coil, points and distributor wiring is OK. This points me to a fuel issue. I have checked and replaced the fuel filter and cleaned and tightened the pump wiring. The pump looked old but seemed to run OK with 12 volts... I do not know how well it maintains a pressure or has an occasional hiccup. My next test is to attach a volt meter in line with the pump. I will drive around the block and if it cuts out yet is still getting 12 volts I will replace it with a new one.

I have read about using a pressure gauge to test the pump, but do not know how to do that or what gauge to buy. I also know nothing about the fuel pressure regulator in my 75 2.0 D Jet system. Is there something here I should check into ?

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.

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.

http://www.914world.com/bbs2/index.php?showtopic=286480

Silly question, but have you checked inside the fuel tank? Your situation sounds like random starvation, which could be caused by junk inside the tank, especially if the filter sock is damaged or mostly-clogged.

Another thing to try is to put an ammeter in line with your fuel pump and go driving around. If the fuel pump is randomly cutting out, you'll see the amps drop to zero then jump back up when the engine catches again.

Putting a fuel pressure gauge in the hoses connecting your fuel injector rails would also work. The simplest way is to put a "tee" in the fuel line and run a hose and mechanical gauge into the passenger compartment and have someone watch it while you drive around. If it drops when you get a cutout, you'll know the problem is in the fuel system, but not necessarily where. Be careful doing this, since you'll have pressurized fuel running into the passenger compartment and the potential for leaks (and worse). IIRC, normal fuel pressure for the D-Jet system is 28-29 psi.

Another day working on the baby. I took a spin around the block a few times with the fuel pump connected to a volt meter. After a few laps the engine started to sporadically started to cut out and the voltage to the pump went to Zero each time. So the pump and the fuel tank are not the issue. Before the rain started I had a chance to pull the pump relay and check it using the headlight. It seems to be OK. I now am trying to study what activates this relay. As always I am appreciative of any suggestions where to look next. I recall someone posted his issue with the fuel pump not activating and as a temporary fix he hot wired it. I may need to go this route if I finally need to take this car to a shop. Not ready to quit yet.

Ahem: "Dielectric grease, or tune-up grease, is a silicone-based grease that repels moisture and protects electrical connections against corrosion. ... The grease does not conduct electricity, so it shouldn't be applied directly to the mating surfaces (pins and sockets) of an electrical connection."

Use a good contact cleaner and leave the pins/seats dry.

For the record, dielectric grease does not conduct electricity. It acts like an insulator.

From Google: Dielectric grease, or tune-up grease, is a silicone-based grease that repels moisture and protects electrical connections against corrosion. ... The grease does not conduct electricity, so it shouldn't be applied directly to the mating surfaces (pins and sockets) of an electrical connection.

So dumb question......

Where is your fuel pump located?

Post a pic

A couple of things. First, the FI Power Supply relay provides power to it; that is triggered by the ignition switch being in the "run" or "start" positions. Second, the FI ECU provides the ground that switches on the pump relay. It does that based on several criteria, notably "is the starter cranking" and "are the trigger points closing periodically".

The power that the relay switches is provided by one of the two fuses on the relay board; I forget which one.

The fuel pump circuit also powers the Aux Air Valve. It might be worth unplugging that and isolating the wire just to take it out of the equation.

--DD

If the engine cuts out, it's an electrical issue. Pull the FI harness and check the wires for continuity while moving the wires. I had to replace a few wires that were cracked and brittle.