Yet another D-Jet problem, UNCLE Options

[r3dplanet]

I'm having the worst time with my 914 this year. Since I've pulled it from the garage this Spring it has run terribly. I've been replacing and fixing and updating the D-Jet parts for some time now. Last year it ran super toward the end of the drivable season, but after sitting for seven months now suddenly it isn't.

Here's what I've done:

The CHT sensor is brand new and correctly installed.
The cold start injector appears to work correctly.
The TPS has a new circuit board and is adjusted (double checked just now) according to the Pelican article.
The AAR works perfectly after a rebuild and closes correctly after ten minutes.
The MPS has been rebuilt (by me) and the behavior is identical to a known good MPS. Using the table at the pbanders website, the car won't idle at all because it runs so lean it pegs the needle on the AFR gauge.
The vacuum lines are all new. A smoke test confirms NO VACUUM leaks, which I would have thought to be the obvious culprit.
The throttle valve has been rebuilt (by me).
The timing is dead on a 27 degrees at 3500rpm.
The fuel lines are all new (stainless + new lines).
The fuel pressure is set to 29psi - but strangely the inline gauge I have shows a rather jittery needle which it didn't used to do.
The car has a mostly 1973 1.7 liter engine.
I've tried two different ECU modules - one from 1971 without the adjustable idle mixture knob which is the one I've been using and a known-to-be-good ECU from a 1973 (037) with the knob, which made no difference where it was set.

My main issues at this moment are (a) very erratic readings from the AFR gauge and (b) high idle. The idle will eventually sit at about 1200rpm once hot, but it will fall no lower. If I tighten the air bleed screw all the way in it continues to idle at 1200rpm. But I unscrew the air bleed valve the idle does increase a tad.

If I adjust the MPS inner screw to achieve a richer burn (say to 13-14:1), the car starts right up and idles, albeit 300rpm too high. If I drive it at cruise it runs super rich at 11 or 12:1. Partial throttle is okay at 14-15.5:1 but then it suddenly just pegs lean, chokes, sputters, and then recovers. This seems to happen at random. If I hit full throttle it begins to rev up but then chokes on a lean condition, but faster than just partial throttle.

I AM CONFUSED.

[Porschef]

I think your smoke test failed. Sounds like another vacuum leak...

Try reusing your old CHT sensor first...Just for kicks

Then your fuel filter....

If I'm wrong, I eat a bug....

[r3dplanet]

Well, if there's a vacuum leak it isn't coming from the main vacuum hoses. I shot numerous small spurts of carb cleaner without noticing any blips in the idle.

I've disconnected all of the lines from the plenum except for the MPS - but also without success. So tightened down the intake runners at the heads. Those gaskets are new, as are the injectors and seals. A few of the bolts were a tad loose but nothing consequential. The tube gaskets that connect the runners to the plenum are new and clamped with nice clamps.

But I did find some new things:

1. According to my fancy timing light, the tach on the dash is 250-300 rpm too high. Weird. I have no idea why that would be the case.

2. With the air cleaner off, I can plug the hose that connects to the air cleaner, and then to the small vacuum connector, which splits off and connects one hose to each head. When that I happens the idle drops to 770rpm. That is with the idle air bleed at full tightness. But if I open the air bleed screw the idle increases quite easily.

3. Strange: if I reconnect the air cleaner and plug the hose that connects the heads to the air cleaner, the idle sits at 1050. So merely by installing the air cleaner the idle jumps over 200rpm.

Still confused.

[r3dplanet]

Well, I took it for a small spin around the block. The idle, even a touch high at 1000-1050, is probably acceptable. I'm still not sure why the air cleaner increases the idle.

But at the least the idle is stable. Now the major problem is just very lean partial throttle. As in 17:1. I have no idea how to change just the partial throttle mixture.

[jcd914]

I have had:
1 intake plenum that had a crack in it.
1 intake plenum that had rust holes in the bottom.
1 throttle valve that would sit off center and bind while closing.

All of these caused high idle speed.

If the throttle valve is closed and the idle screw is bottomed out and the idle is still high, air is getting in somewhere else. It can't idle high without air from somewhere.

Not sure what causes lean mixture atpart throttle but I suspect it is related to MPS adjustment.

Good luck
Jim

[Cap'n Krusty]

Well, I took it for a small spin around the block. The idle, even a touch high at 1000-1050, is probably acceptable. I'm still not sure why the air cleaner increases the idle.

But at the least the idle is stable. Now the major problem is just very lean partial throttle. As in 17:1. I have no idea how to change just the partial throttle mixture.

The idle rises with the air cleaner installed 'cause it fattens up the mixture.

The Cap'n

[r3dplanet]

For sure it must be extra air coming in. I can't even adjust the MPS rich enough to smooth it out, so it's extra air for sure. The TPS is completely perfect. I believe the plenum is good also simply because I pulled it a while back, blasted it, and painted it. Didn't notice any cracks but I suppose it's possible.

If it isn't any of the places I've checked I have no idea where else to look.

I have had:
1 intake plenum that had a crack in it.
1 intake plenum that had rust holes in the bottom.
1 throttle valve that would sit off center and bind while closing.

All of these caused high idle speed.

If the throttle valve is closed and the idle screw is bottomed out and the idle is still high, air is getting in somewhere else. It can't idle high without air from somewhere.

Not sure what causes lean mixture atpart throttle but I suspect it is related to MPS adjustment.

Good luck
Jim

[76-914]

go swap your MPS and ECU with one from a buddy's car that runs well. and what is the hose that connects both heads to the air cleaner?

[r3dplanet]

I've done that. I had a matched-pair, known good MPS and ECU. Same results. Only leaner.

Some engines had small 13mm ports right by the injectors - one on each side of the motor - where a vacuum line is connected. I forget exactly what they're called. It seems to me like a sort of PCV system, even though the car already has a PCV valve.

go swap your MPS and ECU with one from a buddy's car that runs well. and what is the hose that connects both heads to the air cleaner?

[worn]

For sure it must be extra air coming in. I can't even adjust the MPS rich enough to smooth it out, so it's extra air for sure. The TPS is completely perfect. I believe the plenum is good also simply because I pulled it a while back, blasted it, and painted it. Didn't notice any cracks but I suppose it's possible.

If it isn't any of the places I've checked I have no idea where else to look.

I have had:
1 intake plenum that had a crack in it.
1 intake plenum that had rust holes in the bottom.
1 throttle valve that would sit off center and bind while closing.

All of these caused high idle speed.

If the throttle valve is closed and the idle screw is bottomed out and the idle is still high, air is getting in somewhere else. It can't idle high without air from somewhere.

Not sure what causes lean mixture atpart throttle but I suspect it is related to MPS adjustment.

Good luck
Jim

Are you saying that you are adjusting your mps? If so, I found very similar results at first. Do you have an inductance meter to work with. I cannot say enough about pbanders work, but it stops short of getting the car running. I ended up making three new mps units and adjusting them differently. I made graphs of vacuum vs inductance and those helped me see where I would be rich and where I would be lean, and together with the af readings made progress. I do not see how it would work without both the inductance curve on the bench coupled to the af readings in practice.

[worn]

Sorry, pushed add twice

[r3dplanet]

Yes - I'm making adjustments to the MPS. I used my Waketek LCR55 to set the values on the bench to exactly what the pbanders site shows. Using that as a starting point, I then set about making adjustments via my AFR gauge.

For sure it must be extra air coming in. I can't even adjust the MPS rich enough to smooth it out, so it's extra air for sure. The TPS is completely perfect. I believe the plenum is good also simply because I pulled it a while back, blasted it, and painted it. Didn't notice any cracks but I suppose it's possible.

If it isn't any of the places I've checked I have no idea where else to look.

I have had:
1 intake plenum that had a crack in it.
1 intake plenum that had rust holes in the bottom.
1 throttle valve that would sit off center and bind while closing.

All of these caused high idle speed.

If the throttle valve is closed and the idle screw is bottomed out and the idle is still high, air is getting in somewhere else. It can't idle high without air from somewhere.

Not sure what causes lean mixture atpart throttle but I suspect it is related to MPS adjustment.

Good luck
Jim

Are you saying that you are adjusting your mps? If so, I found very similar results at first. Do you have an inductance meter to work with. I cannot say enough about pbanders work, but it stops short of getting the car running. I ended up making three new mps units and adjusting them differently. I made graphs of vacuum vs inductance and those helped me see where I would be rich and where I would be lean, and together with the af readings made progress. I do not see how it would work without both the inductance curve on the bench coupled to the af readings in practice.

[SLITS]

go swap your MPS and ECU with one from a buddy's car that runs well. and what is the hose that connects both heads to the air cleaner?

Head port (2) to anti-flashback valve. Hose from anti-flashback valve runs to air cleaner. Function = crankcase pressure relief and in case there is a backfire, the gasses in the head/crankcase are not supposed to ignite (anti-flashback valve).

And the plenums do suffer from cracks.

[FourBlades]

Try a new fuel filter.

May be partly clogged causing your pressure to flutter.

That would explain not being able to accelerate, you are not getting large amounts of fuel when needed.

Runs rich at idle because you fattened it up in the low fuel demand range.

Be a cheap box to check off.

John

[toadman]

Try a new fuel filter.

May be partly clogged causing your pressure to flutter.

That would explain not being able to accelerate, you are not getting large amounts of fuel when needed.

Runs rich at idle because you fattened it up in the low fuel demand range.

Be a cheap box to check off.

John

I agree. You may also have a kinked fuel line underneath the tank. You indicated that fuel lines were replaced. Finally, are you sure the debris screen (sock) inside the gas tank is clean?

[Dave_Darling]

Sounds like your PCV valve may be open more than it should. Check through the article on Brad Anders' site about the PCV. I have also heard of people putting a restriction in the PCV hose that hooks up to the oil filler.

Borrow another fuel pressure gauge to double-check yours. I had a bad one that read too high, threw off everything when I was using it to set my pressure.

--DD

[r3dplanet]

Everyone, thanks for the responses.

Today I spent the whole day retracing my steps and I found a few small problems. I re-adjusted the valves. They were good before but now are a touch quieter. I also got to thinking that maybe my timing was too advanced, despite having it spot on. So I took a step back to verify the TDC mark on the flywheel and found that the PO had helpfully put it in the wrong place. Only by one "fin", but I am looking for small problems. So I retarded the timing by two degrees. This seems to have tamed the idle issue.

I also checked the plugs (clean), air filter (clean), and ordered a new fuel filter just to check it off the list as fourblades and toadman suggest. Last year along with the fuel lines I also pulled the fuel tank, boiled it clean, powder-coated it, replaced the fuel sock, and coated the inside with POR15. I peeped inside the tank and everything looks sparkling clean. It seems unlikely that the filter is at fault, so perhaps it's possible that one of the front fuel lines has a kink.

Other small items: DD mentioned the PCV valve. Here's something I didn't put together about my engine until today. While the car is a '71, the engine is a '73. I realize that what I thought was a PCV valve isn't. It's just a relief chimney, not unlike the flashback valve. Apparently, the '73 1.7 liter is supposed to have a PCV valve. It's a change from the '71. But I don't think this is actually causing any problems given that the motor is getting plenty of crankcase pressure relief.

I also noted that the electrical connector for the TPS fit loosely. The harness is new. Removing the connector I found that two wires had fallen out of the plastic connector. I thought for sure this would be my problem. But it wasn't. I secured the wires but it didn't solve anything. Most likely I loosened them accidentally when removing the elbow.

Finally I decided that I should't necessarily be trying to adjust my way out of all of this with the MPS. The system just shouldn't be that far out of whack. So I set the MPS back to the values from the pbanders site thinking that those values are far more correct than any of the goofy adjustments I've made to force it to run. Setting the MPS back to default values makes the engine almost too lean to start and idle.

This gives me pause. If my other faulty condition is that if I hit partial load the AFR soon leans overboard and sputters before recovering. Similarly, if I'm parked and rev the engine to 2500 rpm it will do it all day. Or 3500. Or 4000. But the second I let off the throttle the AFR pegs lean, the engine stumbles almost to a stall, and then recovers.

Does this perhaps sound more like a fuel starvation issue than a vacuum issue? I am confident at this moment that there are no vacuum leaks. Or a D-Jet component issue? Taking a step back and trying to wipe my mind clean, never mind what I've already tested. What would cause the engine to fall to a stall via a lean condition after letting up from the throttle?

WCR is in seven days. Ack...

[r3dplanet]

And just because everyone likes glam shots, here's the beast we're dealing with as of this afternoon.

[larryM]

oh, my .......... I'm so glad I sold my last D-jet car 7 yrs ago

[r3dplanet]

A D-Jet equipped 914 is a capricious mistress. She's like the sea. You can play in her, but you cannot play with her.

oh, my .......... I'm so glad I sold my last D-jet car 7 yrs ago