Engine died at autocross event, How embarassing! Options

[toadman]

RESOLVED - See last post by me.

Background - I put my car up for the winter early last December. Car is a 1976 914 with stock fuel injection. Filled it with gas and some Sta-bil fuel stabilizer. Car was running very well when put up. In March I replaced my Pertronix Ignitor with a Compu-fire unit. Car ran well around the block but did not have much time on the Compu-fire until recently when I drove it to a local autocross event.

Drove about 30 minutes to the event with no problems. I made one run and got in line for the next one. Idle started to fall while I was in line. This was not unusual as the car has a history of a weak idle when hot. Car ran well for run two but the engine died on the way back the line.

I had no idle but I could get the engine to run (poorly) if I gave it lots of gas. Exhaust was very rich. I carry a lot of spare parts all the time, including a known, good MPS. I replaced the MPS but it didn't help. I could not diagnose the problem at the event so I got a tow home.

What I have done - I removed the distributor, cleaned things up a bit, including the trigger points, removed the Compu-fire unit and installed points and condensor and reinstalled distributor in engine. No change.

I got my hands on a VW/Grundig fuel injection tester and everything checked out OK except one thing - test number 15 indicates "Open circuit, poor connections or defective pressure switch". The repair instructions were "Check pressure switch, connections and cables. Replace pressure switch if necessary. Look for modified wiring harness". This is not unusual as I have identified this condition in the past and the car ran well, except for the weak idle when hot, for years until now. I have had this harness out of the car for evaluation and I am aware of a short splice of black/purple wire from the FI harness to the negative coil terminal. I know this is a soldered splice as I made this repair.

I used a timing light to confirm spark at all cylinders.

I replaced the fuel injection brain with a known, good unit. No change.

I replaced the cylinder head temp sensor with a new unit. No change.

I cleaned the grounding point beneath the relay board behind the driver's seat, the battery-to-body ground and the fuel injection grounding points on the engine block above cylinder 3. No change.

I removed electrical leads, one at a time, from the intake air temp sensor, the thermo-time sensor, cold start valve and the TPS. No change.

Observations - After trying to start the car, plugs 2 and 3 are wet and plugs 1 and 4 are dry. Does this mean that there is no combustion at cylinders 2 and 3? When I removed the passenger side (cylinders 3 and 4) intake runners to clean the FI grounding point, both intake runners were wet with gas.

I am totally stumped and would appreciate any advice.

[r_towle]

The wiring to the manifold pressure sender needs to be tested from the ECU to the sender.

same test for the Throttle position switch

also, simple visual....check the Cylinder head temp switch, and make sure it plugged in, and had proper readings when cold..

Car won't start with a bad CHT
car won't start with the MPS unplugged.

car will start without the Tps, ambient air temp, AAR, etc.

[stugray]

I cant help with the specifics of your FI troubleshooting, but I can lend some advice about troubleshooting in general (after 6 hours troublehotting a spitfire ignition problem).

Go back and verify that everything you state as fact is REALLY a fact.
Simple statements like "we took the rev limiter out" can waste many hours of effort and then you learn "Oh yeah.... well we put it back in"..

[Java2570]

I would suspect the issue lies somewhere within your wiring harness. If it's an original harness, you could very well have bad individual wires or connectors that get worse
as the engine heats up. Perhaps the injector wires or injector plugs/grounds or
CHT wiring.....
Once these old harnesses start cracking and wearing out, there's no telling what can happen and when. Start at the ECU connector and test all the components, that way you will see if there's a wiring issue in a specific area or component.
http://members.rennlist.com/pbanders/DJetParts.htm -- scroll down this link and he outlines how to do these tests.

[Cap'n Krusty]

In a D-jet system, there is no wire in the FI harness that connects to the coil.

The Cap'n

[toadman]

In a D-jet system, there is no wire in the FI harness that connects to the coil.

The Cap'n

Cap'n, you are correct. Black/purple wire to coil is an ignition harness wire.

[toadman]

Thanks for your responses.

R_towle and Java 2570, if I am to believe the VW/Grundig tester I used to test the FI wiring to the TPS and CHT and wiring to all of the other components except the MPS, is good. The components are also good.

I have tested the MPS electrically and with vacuum. Electrically it is fine. It does leak slightly but has been working this way for a long time. I also have swapped in a known, good MPS and that did not correct the problem so I don't think the problem is the MPS unit, itself. That makes me think that the MPS wiring may be the culprit and the VW/Grundig tester indicated that this was "Not in order". Even though it has been this way for a long time, I will focus my attention on this part of the harness.

For what it is worth, fuel pressure is good. I have an in-line pressure gauge. Also, I hear clicks in the engine bay (injectors?) when the key is on and I slowly depress the accelerator. I believe this is an indication that the TPS is good.

[r_towle]

Thanks for your responses.

R_towle and Java 2570, if I am to believe the VW/Grundig tester I used to test the FI wiring to the TPS and CHT and wiring to all of the other components except the MPS, is good. The components are also good.

I have tested the MPS electrically and with vacuum. Electrically it is fine. It does leak slightly but has been working this way for a long time. I also have swapped in a known, good MPS and that did not correct the problem so I don't think the problem is the MPS unit, itself. That makes me think that the MPS wiring may be the culprit and the VW/Grundig tester indicated that this was "Not in order". Even though it has been this way for a long time, I will focus my attention on this part of the harness.

For what it is worth, fuel pressure is good. I have an in-line pressure gauge. Also, I hear clicks in the engine bay (injectors?) when the key is on and I slowly depress the accelerator. I believe this is an indication that the TPS is good.

Clicks do not indicate it's good, just that you get contact sometimes..

There are 21 or 22 clicks, and it needs to be set exactly right.

Regardless, I would verify the wiring for the mps....
Sucks, but maybe open up the loom and replace those wires.

From what I recall, you can pull out the FI wiring harness in a few minutes and get it on a bench for surgery...

[struckn]

[/i][i]Observations - After trying to start the car, plugs 2 and 3 are wet and plugs 1 and 4 are dry. Does this mean that there is no combustion at cylinders 2 and 3? When I removed the passenger side (cylinders 3 and 4) intake runners to clean the FI grounding point, both intake runners were wet with gas.


Are you blowing Gas out the exhaust? If so you may have a couple open exhaust valves from dropped seals. Check you valves
and if they are out of adjustment you may have to pull the heads.

[toadman]

[/i][i]Observations - After trying to start the car, plugs 2 and 3 are wet and plugs 1 and 4 are dry. Does this mean that there is no combustion at cylinders 2 and 3? When I removed the passenger side (cylinders 3 and 4) intake runners to clean the FI grounding point, both intake runners were wet with gas.


Are you blowing Gas out the exhaust? If so you may have a couple open exhaust valves from dropped seals. Check you valves
and if they are out of adjustment you may have to pull the heads.

Solved - I gave up trying to diagnose this issue and had my car towed to a local shop.
Doug N., you were on the right track. I should have checked the valves before I sent it to the shop. The shop did a compression check and found no compression on cylinder 2 and compression values of 90 - 100 on the other three cylinders. They found brass shavings in the valve cover for cylinders 1 and 2. They said they used a boroscope and observed a bad intake valve guide at cylinder 2. Looks like I am going to drop the engine for a rebuild. Probably going to larger pistons and cylinders (2056).

[rnellums]

Sorry to hear about this! More power out of a rebuild will be good though!