Problem Resolved [was I'm Stumped], Runs briefly, then dies & won't restart Options

[ThinAir]

Background: In preparation for last year's RRC I fixed the mounting on the MPS of my son's stock 1971 914-4. All seemed well until we went out for the Saturday morning run - we turned a corner and the engine suddenly died and was clearly flooded. It restarted quickly, but we had the same problem several times on that trip after that.

I assumed that I had disturbed something electrical on the passenger side of the engine and in digging around I discovered that the wire connecting the Cylinder Head Temp Sensor was corroded at its base (in fact it fell off in my hands). Ok, this is simple I said - so I bought and installed a new CHT.

Current Problem: The engine will start, but runs for only about 30 seconds before it dies. At that point it will not restart, but it smells of fuel as if it is flooded. I've checked for spark and I have spark. I've disconnected, cleaned and reconnected every electrical connection on the engine & relay board that I can find - including every relay on the board. The only connections that I have not checked are the connector where the FI harness connects to the brain.

Does anyone have any ideas on what could cause this and where to look next?

[ejm]

Check the fuel pressure. Maybe the regulator is bad or the return line is pinched.

[ThinAir]

Well... the mystery deepens!

Right after posting I went out, removed the air-cleaner snorkel and sprayed some starting fluid into the throttle, then cranked and cranked with the accelerator pedal to the floor and eventually it started. Once it started there was a big puddle of fuel on the driveway behind the exhaust.

Although I was able to get it restarted again on several occasions, I just couldn't keep it running sooo...

I removed the air cleaner and checked the paper filter. It looks pretty gross and there is some oil in the bottom of the air cleaner body so I left the filter out and put the the assembly back onto the snorkel. As soon as I would get the filter assembly within 1/2 inch of the snorkel the engine would stall.

Opening the idle bypass sort of took care of this situation, but seemed strange since this has been fine for thousands of miles. Because I had noticed some oil-smoke coming from the crankcase ventilator hose I decided to remove the oil filler cap and discovered that if I left the cap off I could keep the engine idling even with the air cleaner assembly installed, but as soon as I put the cap back on the engine would die.

Further experimentation shows that if I remove the electrical connector from the MPS I can still get it started with the accelerator to the floor, but the engine won't idle and won't rev smoothly.

So at this point I'm thinking that I've got a bad MPS. Does this sound reasonable?

[ThinAir]

A check of Pelican Parts has this description of the MPS:

"The pressure sensor is the key component of the MPC (Manifold Pressure Control) D-Jetronic fuel injection system. Its function is to measure the amount of vacuum being drawn into the engine. Based on the amount of vacuum being drawn, it sends a electrical signal to the fuel injection computer. Based on this signal, as well as the two temperature sensors mounted in the system, it controls the fuel-air mixture. When these sensors fail, they typically cause the engine to run rich at all times and lose power under acceleration."

That sounds like it fits pretty well with what I'm experiencing. Of course PP also says it's NLA. Does anyone know of a source?

[ThinAir]

Thank goodness for spare vehicles! A guy gave me a 74 carcass a couple of years ago with no engine or tranny... but it still had a MPS!

Swapped out the MPS and all the same behaviors are there so it's pretty clear that I have a wiring harness issue that is associated with the MPS, but the MPS is fine.

So now I have 2 choices for my son:
1. Trace down the broken wire and patch it
2. Get a Bowlsby FI wiring harness

I'm voting for #2!

[justdrive914]

A check of Pelican Parts has this description of the MPS:

"The pressure sensor is the key component of the MPC (Manifold Pressure Control) D-Jetronic fuel injection system. Its function is to measure the amount of vacuum being drawn into the engine. Based on the amount of vacuum being drawn, it sends a electrical signal to the fuel injection computer. Based on this signal, as well as the two temperature sensors mounted in the system, it controls the fuel-air mixture. When these sensors fail, they typically cause the engine to run rich at all times and lose power under acceleration."

That sounds like it fits pretty well with what I'm experiencing. Of course PP also says it's NLA. Does anyone know of a source?

Of course there are places to get them, Auto atlanta for around 240.00 plus and performance products for around 190.00, lots of used parts people to, German auto dismantlers and many others

[swl]

Thank goodness for spare vehicles! A guy gave me a 74 carcass a couple of years ago with no engine or tranny... but it still had a MPS!

Swapped out the MPS and all the same behaviors are there so it's pretty clear that I have a wiring harness issue that is associated with the MPS, but the MPS is fine.

So now I have 2 choices for my son:
1. Trace down the broken wire and patch it
2. Get a Bowlsby FI wiring harness

I'm voting for #2!

If you want to invest some time in #1 I have a set of multimeter readings that can give you a pretty good indication of the entire system. They are documented here http://www.914world.com/bbs2/index.php?showtopic=70441

[ThinAir]

If you want to invest some time in #1 I have a set of multimeter readings that can give you a pretty good indication of the entire system. They are documented here http://www.914world.com/bbs2/index.php?showtopic=70441

Thanks Steve! That looks very helpful. I hadn't looked at any wiring diagrams yet to see what connected to what so that I could test this kind of thing.

[orange914]

test the mps for vacuum leakage.

what about the cold start valve? see if the fuel pressure leaks down after you shut it off. if it does remove the cold start valve (keep hooked up to fuel line), cycle the key to build fuel pressure and see if it leaks.

mike

[BMXerror]

Because I had noticed some oil-smoke coming from the crankcase ventilator hose I decided to remove the oil filler cap and discovered that if I left the cap off I could keep the engine idling even with the air cleaner assembly installed, but as soon as I put the cap back on the engine would die.

Are we completely ignoring this? I'd check your dipstick to see how much gas you have in your crankcase. You could be hydro-locking your case. This can LITERALLY explode engines, not to mention that it's not so good on the rings and bearings. So if the oil's real runny and smells of gas, err on the safe side and give her an oil change. It's possible that your first issue was with the CHT sensor, and that flooded the case(ask how I know). This may not be all of your problem, but it sounds like a good candidate for some of it.
It also may be that your crank case breather is clogged and it won't overcome the crankcase pressure at idle. Pull your breather and filter (box at the front of the engine) and clean them, see what happens. If there's still rich issues, come back and we'll work from there.
Mark D.
BTW, Bleyseng rebuilds MPS's and sells them for a lot cheaper. But that's not the problem near as often as people think it's the problem.

[BMXerror]

Oh yeah. Another thing. Before you go searching for bad wires, get a wiring diagram and make sure it's hooked up correctly.... again. Ask me how I know.
Mark D.

[toon1]

Check the MPS for vacume. the MPS from the 74 is different than the MPS for the 73 1.7 this will cause issues.

The CHTS might be bad, common prob. .

Have you checked the inj's for leaking?

Have you checked all the fuel lines and vac. hoses?

Check the PCV valve.

Check the fuel filter.

Also, as Mike said( orange 914), check the cold start valve( fifth inj.). They don't go bad often but will sometimes.

[swl]

Further experimentation shows that if I remove the electrical connector from the MPS I can still get it started with the accelerator to the floor, but the engine won't idle and won't rev smoothly.

OK this is really bugging me. With the MPS electically disconnected how the heck is the engine running. My experience with a broken wire to the MPS resulted in none of the injectors working. After reading Brad Ander's stuff I convinced myself that the MPS was doing pulse shaping in the final drivers for the injectors. Break that cct and there is no pulse for the injector. If that is true then where is the gas coming from? The only other source of gas is the cold start valve but it would not be operating because the electrical cct doesn't kick in until it is bloody cold. Maybe Mike is onto something - maybe that valve is stuck open. I can't for the life of me figure out how that would happen but the gas has to be coming from somewhere.

[toon1]

Further experimentation shows that if I remove the electrical connector from the MPS I can still get it started with the accelerator to the floor, but the engine won't idle and won't rev smoothly.

OK this is really bugging me. With the MPS electically disconnected how the heck is the engine running. My experience with a broken wire to the MPS resulted in none of the injectors working. After reading Brad Ander's stuff I convinced myself that the MPS was doing pulse shaping in the final drivers for the injectors. Break that cct and there is no pulse for the injector. If that is true then where is the gas coming from? The only other source of gas is the cold start valve but it would not be operating because the electrical cct doesn't kick in until it is bloody cold. Maybe Mike is onto something - maybe that valve is stuck open. I can't for the life of me figure out how that would happen but the gas has to be coming from somewhere.

The MPS DOES the pulse shaping for the inj's.. It tells the ECU/brain how much fuel to deliver to the engine.

My guess would be that the engine is possibly running on a but of residual fuel OR and inj. is leaking in to the cyl. which would let it continue to run.

Either way the is quite a bit of diagnosing to do.

[ThinAir]

I have not yet gotten back to this to try and prove that it's a broken wire, but I do want to put to rest one thing - this engine does not have an operating cold start valve. It's been bypassed for several years so it was already out of play when the original problem came up.

One thing for sure - thanks to your advice about the impact of the flooding problems on oil, I'll for sure be doing an oil change before putting it back into service.

[orange914]

I do want to put to rest one thing - this engine does not have an operating cold start valve. It's been bypassed for several years so it was already out of play when the original problem came up.

is the fuel bypassed, not just electrical unplugged, right? does fuel pressure stay up and not leak down after it sits?

mike

[ThinAir]

I do want to put to rest one thing - this engine does not have an operating cold start valve. It's been bypassed for several years so it was already out of play when the original problem came up.

is the fuel bypassed, not just electrical unplugged, right? does fuel pressure stay up and not leak down after it sits?

mike

The electrical is disconnected and the fuel is bypassed. I have not checked how well the fuel system maintains pressure after it has been sitting, but there has never been a hint of a problem with the delivery of fuel through the fuel pump, hoses, injectors until the problem of it stalling and being flooded at that point.

[wilchek]

First, I think you need to narrow down your search and work on one area at a time. First check the fuel pressure with a pressure meter. Harbor freight has them cheap and it will be fine for this purpose. To me it seems that you are thinking much worse than it is. Make sure the head temp sensor is good. IF you are flooding out which you are you should be able to remove the temp sensor and ground the line to the body and this will run at a fully heated setting (more lean). If the car still floods out then it is not the head temp sensor (sounds like this is not the issues). It sounds like one of you injectors are stuck open and the car is running for 30 seconds due to running out all of the fuel that is in the chamber. I think it is running with the MPS disconnected as there is still fuel in the cylinder. The injector can be stuck or the fuel pressure is too high causing the injector to leak. If the pressure is too high replace the pressure regulator, and make sure the return line to the fuel tank is not clogged. If these areas check out make sure the fuel injectors are not stuck open. So now we ruled out MPS, head temp snesor, fuel pressure and injectors. Last think to look at is the wiring. Clean all the contact at the board (which you did) and the ground contact under the airfilter at the base of the intake (all white lines). If this does not work I would bet it is the computer. I know they say that they never go but this is not true. swap a new ECU out with the quick connector under the grey door on the side of the ECU and go.

Steps to check

1. MPS ( sounds good)
2. Head temp sensor and wiring (sounds good)
3. Fuel Pressure (issues could be pressure regualtor, return line, fuel pump,and stuck open injector)
4. Injectors (stuck open)
5. ECU
6. Ground wiring

One of these things above is causing your car to flood out.

[ThinAir]

Well I worked on it a little bit today, but did not manage to change anything. Plans have changed for this car so this is the last effort I'm going to put into this particular project.

Based upon the behavior that I've seen, the circumstances of the problem's start, and reading at Brand Anders FI pages I'm convinced that I broke something in the wiring harness that just isn't readily apparent. That probably means it is in the connector.

I've got a spare FI wiring harness on another engine, but we've also got a 2-liter from my son's wrecked 73 that's just sitting around. At this point we've decided to freshen the 2-liter and then install it in the 70. It's a solid car and the engine was solid at the time of the wreck so it's really a winning combination. We just can't see the effort of putting a different FI harness on an engine that we'll probably replace anyway.

Thanks for all your help and advice.

[toon1]

Well I worked on it a little bit today, but did not manage to change anything. Plans have changed for this car so this is the last effort I'm going to put into this particular project.

Based upon the behavior that I've seen, the circumstances of the problem's start, and reading at Brand Anders FI pages I'm convinced that I broke something in the wiring harness that just isn't readily apparent. That probably means it is in the connector.

I've got a spare FI wiring harness on another engine, but we've also got a 2-liter from my son's wrecked 73 that's just sitting around. At this point we've decided to freshen the 2-liter and then install it in the 70. It's a solid car and the engine was solid at the time of the wreck so it's really a winning combination. We just can't see the effort of putting a different FI harness on an engine that we'll probably replace anyway.

Thanks for all your help and advice.

What are you going to do for a harness for the 2L??

Most of the harnesses suffer the same prob.,old, brittle and corroded connectors. Take a good look at the 2L harness before putting it in to sevice.

Check ALL other componenets BFORE you put them into service or you may be going down the same road your on now. At close to 40yrs. old, most of this stuff is at the end of it's service life