Fuel injection woes

[911buff]

Just finished rebuilding my 74 2.0 and now the fuel injection is acting up. The engine will run for a few minutes when it is cold but as it warms up, it runs rich and then shuts down. It will not restart until I take the fuel pump out of operation, then runs until it is out of gas. Let it cool down and it runs for a while, etc, etc. Both temp sensors ohm out correctly for cold and hot. The MPS ohms out correctly and holds a vacuum. I can not find any vacuum leaks. So I am really in a quandary. The engine was running pretty well before it dropped a valve seat. So, I do not know what has changed. I have gone through the troubleshooting guide on Rennlist and cannot a good solution. I know it has to be a sensor input to the ECU that is causing it to run so rich it shuts it down. But I cannot seem to find a fault. Help, please!

[Dave at Pelican Parts]

How's the fuel pressure?

How's the spark?

Are you hearing anything funny while it runs?

--DD

[911buff]

Fuel pressure at 28psi. Spark appears to be strong. I have always wondered how one quantifies the spark. I think I brought it up once before here but never really got a solid answer. How do I really tell if the spark is "fat" or not? Anyway, while it is running it is strong with no weird noises. When I pull the spark plugs out, they are very sooty! Exactly what I expected. As the engine runs, the smell of fuel builds. If I try to start it after it has shut down, it acts just like a carbed engine when a floats are stuck. It is like it is flooded, which I guess it is. Thanks!

[Rocky14]

I would unplug the cold start valve. With the valve unplugged start and run the car to operating temp. If still rich mixture, disconnect and plug the gas line to the cold start valve and run the car again--if still rich at least you have ruled out the cold start valve is leaking or malfunctioning. I had the same rich problem with my 73 2.0--after going through all the testing you describe, it turned out my cold start valve was feeding gas as the engine warmed up.

[Dave at Pelican Parts]

If that doesn't turn up anything, try digging up a "noid light" to plug into an injector lead. See if it blinks as expected, or if perhaps the injector stays open?

--DD

[911buff]

Thanks. I can't unplug my cold start valve...it is not hooked up. Here in SE Georgia it does not get cold enough to worry with it, so off it went. I have a fuel pressure gauge utilizing the nipple. Anyway, that is not the problem. I wish it were that easy, though!
As for the injectors, if they stay open while the engine is running, would they be stuck open with just the ignition on? With the ignition on, I hear the injectors clicking as I open the throttle.
Could the injection points bounce so much as to cause the engine to choke out? So, I guess my next question is, do I break down and procure new T1 and T2 sensors and try the old "hunt and peck" route? Again, thanks for the advice!

[beatnavy]

I would primarily worry about the CHT (T2). Ambient air intake sensor does not have a massive impact on mixture. If it's disconnected (like I'm actually running right now) it will richen the mixture some, but not enough to make the engine stall. Your symptoms sure SOUND like the CHT either bad, going bad, or disconnected.

How does it run when you first start it cold? Does it seem solid for at least a minute or so?

[911buff]

BeatNavy, First of all, I am going to assume you're Army...But I won't hold that against you. Retired US Navy EOD Technician, here! I have some great memories working with Army. THREE ID (Rock of the Marne), 10th Mountain and a slew of EOD guys from here to Kuwait, to Oman, to Iraq...you name it. And THANK YOU for your Service!!!!! But, ultimately...BEAT ARMY!!!!!!

Anyway, it runs strong for 10 minutes or so, then starts to stumble and then finally dies. If I let it sit for a while, it will runs for a minute or so. But when cold, about 10 minutes. I will look into getting a new T2 sensor and see what happens. Thanks for the advice!

Oh, sorry for 13 straight. Better luck next year!

[beatnavy]

Originally Posted by 911buff

BeatNavy, First of all, I am going to assume you're Army...But I won't hold that against you. Retired US Navy EOD Technician, here! I have some great memories working with Army. THREE ID (Rock of the Marne), 10th Mountain and a slew of EOD guys from here to Kuwait, to Oman, to Iraq...you name it. And THANK YOU for your Service!!!!! But, ultimately...BEAT ARMY!!!!!!

Anyway, it runs strong for 10 minutes or so, then starts to stumble and then finally dies. If I let it sit for a while, it will runs for a minute or so. But when cold, about 10 minutes. I will look into getting a new T2 sensor and see what happens. Thanks for the advice!

Oh, sorry for 13 straight. Better luck next year!

There are sure a lot of Navy guys on these forums ! Yes, I'm Army (and my last duty assignment in Germany was with the 3rd ID -- Rock of the Marne indeed). We got our butts kicked -- again -- but I have to say we at least played about as well as we could. No fumbling on the 1 yard line, missing chip shot field goals, throwing pick sixes, etc. Just didn't have the talent to match up. We beat Navy three out of the four years I was a cadet (not that I had anything to do with it personally), but that was a LONG time ago. This weekend I was at my buddy and classmate's bar in Chapel Hill, NC for "the biggest A/N party outside of the actual game." We go every year, and it's a lot of fun. Tons of Navy guys show up and it's all in good fun. We like to say (every year), "we lose the game, but we win the party." Or at least that's what we tell ourselves . I have to tell you, even some of the Navy guys this year we're saying "You guys gotta win one soon!" It's not good for the rivalry to be this lopsided.

Rock on, thanks for your service as well. What you did is not for the faint of heart. And get that CHT replaced! HOPEFULLY that'll be your ticket. It sure sounds like it if the engine otherwise runs strong for 10 minutes and you've otherwise verified everything else.

[Dave at Pelican Parts]

Note that the CHT likes to pull the threads in the head out if you're not very careful removing it. Running a heli-coil in with the engine in the car is a pain in the butt...

If you have access to an O-scope, it's well worth inspecting the wave form of the trigger points. It is rare, but can happen, that the trigger points bounce enough to inject lots more fuel.

Not sure what else to check off the top of my head. You did check that the MPS holds a vacuum, right? And that the hose from the manifold to the MPS is connected solidly and not cracked?

--DD

[911buff]

Well, finally found the culprit, the wiring was faulty. Wire #23 from the ECU to temp sensor 2 was broken in the sheath. After reconnecting, she started right up! I keep threatening to rebuild the harness, I guess I need to follow thru. But right now it is time to enjoy a drive!

[beatnavy]

Very sweet. Thanks for the update and good luck.

[911buff]

I guess I was too hasty in my celebration! Fuel injection still not functioning properly. The engine is still plagued with a vacuum leak, so I guess. I cannot get the idle below 1200-1400 RPM. My thinking was that the MPS was the culprit. So, I went to troubleshooting. When I suck on it, it seems to hold a solid vacuum. However, when I hook my "mighty vac" to it, it looses the vacuum rather rapidly. So, the only logical step was to tear apart the MPS and see what ails it.

I know, I know but I could not resist.

The O-ring was in two pieces, so I was hopeful. I wanted to check the diaphragm, so more apart it came. The diaphragm was solid, thank goodness! But the paper gasket does not seem like it would be air tight. It was all there and in great shape, so I will trust the German Engineers. Talking over the operation of the unit with a "hot shoe" friend, I now have a question as to the proper sequence of the diaphragm section. I cannot find an exploded view, so I made my own (please forgive any inaccuracies, it was a quick sketch). This was how it came apart.



Is this sequence correct? Or should the "spacer" be a sandwich plate to sandwich the diaphragm to the throttle stop plate?

Anyway, even after replacing the O-ring and reassembling the MPS, it functions the same. Good vacuum when I suck on it but with the vacuum gauge, it dissipates rather quickly. And with the engine running, still cannot get below 1200-1400 RPMs. Any thoughts?

[beatnavy]

That looks to be in the correct sequence. Here's pictures of my MPS rebuild using the Tangerine kit. In order:

1. Installing the Diaphragm (paper gasket already in unit as can be seen)


2. Diaphragm and Spacer installed


3. Throttle stop plate installed


Also, when you checked the vacuum leak, what did you find? I've seen some conflicting guidance on what constitutes "acceptable" in terms of MPS holding a vacuum. I used to think it needed to hold 15 for 5 minutes, but I think more authoritative info (I think from the Anders site) says it shouldn't leak from 15 to 5 in less than a minute. Mine did almost exactly that (leaked from 15 to 5 in roughly a minute or more) both before and after "rebuild."

[beatnavy]

Have we talked about whether you've checked to see if the Auxiliary Air Valve is closing?

[911buff]

I do not have the cold start system installed. The cold start valve is blocked off. Tonight, I pulled out T2 to see if anything was amiss and to check the Ohms hot and cold. I tested both the old one and new one and of course I did not need a new one. Oh well, now I have a spare. They were both right on the money. But I did find that the sensor was not tight, so maybe there was not good continuity. I will find out in the morning if that was the problem. I hope so because I am running out of things to check. Very frustrating!!!!

[beatnavy]

The AAR is different than the cold start valve. When you say you don't have a cold start "system" are you talking about the extra fuel injection from the cold start valve/thermotime switch? The AAR provides extra air when the engine is cold. They often stick in the open position which causes lean condition and high idle. Very common.

On my 1.7 it's located in front of and below the air cleaner slightly to the driver's side. It looks like this: AAR.

If you don't have an AAR then someone did something creative with the air hoses that normally go to that.

It's easy to check whether or not it's failed open or closed. Read Anders' information on it: D-Jet Reference

About halfway down the page there's a lengthy description of the Auxiliary Air Regulator. Maybe this is or is not your issue, but worth checking.

[911buff]

Both cold start valve and AAR are removed from the engine. Blocking off the cold start valve eliminates the air access into the distribution box. When I bought the car, it had a non-functioning AAR, so I removed it. And because it rarely gets below 32 degrees down here, it really isn't necessary. And my garage is insulated, so even if it does, the temp never drops below 50. I do enjoy my garage!

I am getting ready to go fire it up and see where I am at. Wish me luck!

[beatnavy]

If the AAR is removed then I'm well out of my depth in giving advice. But I can wish you luck. Good luck!

[911buff]

Victory at last...well, to a point. I had the MPS way out of adjustment. Way too lean! Now the car runs as it should. Just took her for a spirited drive...awesome! The only problem is that I still cannot get the idle below 1400 RPMs. I have checked everything twice (Tis the season, don't you know) but I still cannot find why. I am headed to the auto hobby shop on base to set the correct timing and then I think I will let it go for a while. I need to get to work on my '71 "T". Goal is to be ready for the "Cars and Coffee" at Amelia in March! Thanks for all the advice and encouragement!