Non Running Engine Good Compression and Ignition Spark Present Noid Light Test no Signal

[neon]

Hello coupe folk - On a drive of approx 1 hr, returning, there was a bit of intermittent subtle misfire followed by some rough running and I barely got back. Now will not start.
Compression between 168 and 178 all cyls, spark present at each plug wire, fuel pressure 2.07 bar, ecu voltages partially checked showing correct temperature sensor resistances, correct ECU and Fuel Injector supply voltages, I think OK throttle switch performance ( tough to gauge w VOM only). NOID light test of fuel injectors showed NO flashing of lights to all injectors !!! Fuel injector circuit resistances tested from ECU : pin 3- 5 was 2.6 and pin 4-6 was 3.6 Pin 3 - 5 is in spec pin 4- 6 may be high dont know what to make of it. I have not yet checked the distributor trigger point system ( for the injectors). Fuel pump seems fine, but seems to run continuously. Fuel flows continuously to the rail when the pump actuates. I cannot figure out how to check the trigger signal for the injectors at the ECU and I do not have an oscilloscope, but I could take apart the distributor and measure cam excursion I guess and use VOM to look for rapidly fluctuating signal at he plug. Would appreciate any suggestions on the approach, I have the excellent jetronic.org web site and have been following those sometimes tough to understand instructions

Car has about 1000 mi since last valve adjustment. I have not done any ignition testing other than looking for spark, which again seem fine and strong. Plugs looked great but I need to test them individually ( used one plug only for testing for spark)


I am wondering how to find the fuel injector system relay ? From diagrams and the shop manual, and various wiring diagrams, I cannot yet figure out if there is a separate relay that may control fuel injectors ?

Best to all
Dana in CT ' 73 Fjord Blue CS w many CSL parts- I just finished a decent DIY interior refresh when this happened !!

 

[mulberryworks]

To quote our own Hack Mechanic, "It's always the points."

Ok, it's not always the points, but your symptoms remind me of how my car was running when I bought it and it was indeed the points (and a failing distributor adding its own symptoms). I have Zenith carbs and you have fuel injection so there are more things to check, but you gotta check the timing early on in your diagnosis. Good luck.

 

[Aussiecsi]

I suspect it's either faulty MPS or bad connection /broken wire . You will need a D-Jet wiring diagram to test for continuity . I had a similar issue and it turned out to be a broken wire inside the plug that connects to the MPS ....would never have found it without doing continuity test of injector harness. Good luck .....it can be quite a frustrating process but I'm sure it will be something "simple "....it always is !

 

[neon]

I suspect it's either faulty MPS or bad connection /broken wire . You will need a D-Jet wiring diagram to test for continuity . I had a similar issue and it turned out to be a broken wire inside the plug that connects to the MPS ....would never have found it without doing continuity test of injector harness. Good luck .....it can be quite a frustrating process but I'm sure it will be something "simple "....it always is !

Thanks Aussie csi:

MPS = Manifold Pressure Sensor ? otherwise known as MAP sensor ?

Dana

 

[sfdon]

thoughts for you.

Aussie is correct- if your MPS is not connected, the engine will not fire.

Also- if your Noid light is not flashing then all the compression and spark and fuel pressure in the world won’t matter.

You should check for ground first at the left plenum support. That is the ground point for your injectors. If your Noid light isn’t flashing-It seems likely that your injectors are not getting the signal to fire.

The e9 forum Djet lending library maintains most everything you might need to try to find your problem.

We have extra large (2’ x 3’) Djet schematics with key (2pcs)
ecu
MPS
TPS
Trigger points

Note- the lending library items are NOT for sale.

you only have to ask and pay for shipping to and from your location.
we lend out for 2 week maximum

if you need help locating a replacement part for a part that is defective we’re happy to help but all of the materials must return within two weeks

LMK

Sfdon

 

[sfdon]

I suspect it's either faulty MPS or bad connection /broken wire . You will need a D-Jet wiring diagram to test for continuity . I had a similar issue and it turned out to be a broken wire inside the plug that connects to the MPS ....would never have found it without doing continuity test of injector harness. Good luck .....it can be quite a frustrating process but I'm sure it will be something "simple "....it always is !

• Failure Modes
  • Open or shorted primary or secondary coils: Results in no injection pulses, the car is inoperable.
  • Vacuum leaks: Depending on the extent of the leak, the car can run slightly rich to very rich across the entire load range.
  • Failed aneroid cell: Causes the car to run rich at idle, with poor part-load response.
  • Maladjustment: Many owners and mechanics have tried to adjust the sensor by removing the epoxy-covered "plug" and turning the adjustment screw inside - this often results in unpredictable behavior, as adjustment of this sensor accurately requires a bench setup that only a few shops have.
• Notes: This is the most important sensor in the D-Jetronic system. As noted above, make absolutely certain that the sensor you have is properly matched to your FI setup. Mismatched sensors can cause drivability problems.

 

[sfdon]

And now for the trigger point explanation…

• Function: Sends timing pulses to the ECU to provide engine speed data and synchronize injection pulses.
• Failure Modes:
  • "Bouncing" or dirty contacts: A "bouncing" contact causes multiple injection pulses to be generated, resulting in a very rich mixture. Can only be checked by using an oscilloscope.
  • Dirty (intermittent opens) contacts: Dirty contacts can result in missing injection pulses, leading to bucking and drivability problems. Can only be checked by using an oscilloscope.
  • Open contact (not switching): Causes one bank of injectors to not fire. Easy to check with a noid light that plugs into your injector connector. Available from local auto parts stores (e.g. Checker).
  • Worn cam rubbing blocks: When the blocks wear down very low, both switches turn "on" for most if not all of the rotation of the shaft. When both switches are on, this can lead to a no-start situation and very erratic operation.
  • Misaligned switch: There is a fair amount of "slop" in the fitting of the switch to the distributor than can lead to problems. Make certain the switch is in the middle of the range of positioning in the distributor body.
• Notes: These contacts are very low current and are reliable, lasting in excess of 100K miles. Make sure if you install new contacts that you use a dab of Bosch distributor lube on the distributor contact lobes. Failed trigger contacts will prevent your car from starting and running. Later models of the contacts have a shield that keeps the lube from being sprayed onto the contact points.

 

[sfdon]

You need to ohm out 4 connectors at the MPS all the way to the ECU.

 

[neon]

You need to ohm out 4 connectors at the MPS all the way to the ECU.

View attachment 150945

 

[neon]

Sdon - wow a wealth of information I do appreciate.

Do you know if there is a relay controlling the fuel injectors - cannot find it anywhere, on diagrams or shop manual, but suspect it exist.

When you say "ohm out" do you mean test for continuity from each of the MAP sensor connectors all the way to the ECU, or actually measure for "in spec " resistances which I think should be a straight conductor path with close to zero ohms. Thanks !!

Dana in CT where the closest e9 shop is 300 mi away !!

 

[sfdon]

Injectors use Drivers. The Drivers are inside the ECU. They are electronic switches.

There is a Main Relay. It provides power to pin 16 and 24 of the computer.

Do you have a spare main relay? You need one!

 

[neon]

sfdon - thanks I guess that crosses off the "hope" that I have a bad relay I have proper voltage to pin 16 and 24 so I can conclude main relay ok as far as the injection system is concerned - correct me if wrong

i noticed that what I think are resistors, sitting just behind the brake vaccum booster cannnister, are not connected. There are several wires in this car under dash not connected so i never paid these any mind. However, if I understand some shop manual photo correctly, these are associated with the signal to the injectors. Is that what I am looking at here in the attached photo ?

thank you
Dana

 

[neon]

sfdon - thanks I guess that crosses off the "hope" that I have a bad relay I have proper voltage to pin 16 and 24 so I can conclude main relay ok as far as the injection system is concerned - correct me if wrong

i noticed that what I think are resistors, sitting just behind the brake vaccum booster cannnister, are not connected. There are several wires in this car under dash not connected so i never paid these any mind. However, if I understand some shop manual photo correctly, these are associated with the signal to the injectors. Is that what I am looking at here in the attached photo ?

thank you
Dana

 

[Dick Steinkamp]

I think those are just wire connectors.

 

[HB Chris]

Probably on all coupes but on the carb car it runs the water chokes and enrichment devices.

 

[sfdon]

Did you pin out the MPS?

 

[bill]

Allow me to add a few things to SF Don's excellent suggestions. Having had problems with the MAP and Throttle Position Switch, I hope I can help. The main relay is located (usually) in front of the brake booster: there are two relays there, the one on the left is the main, the one on the right is the Cold Start relay. There is no separate relay that controls the injectors. If the Main relay is bad, you won't get power to the ECU via wires 16 (powers the computer) and 24 (powers the injectors.)


The MAP should hold a 15" vacuum for at least 10 seconds. If not, the copper diaphragm in the MAP is torn and the MAP will have to be rebuilt. A MAP with a torn diahragm makes the ECU think the engine wants to accelerate real fast and will dump a lot of gas into the engine ALL THE TIME...result, much smoke and poor driveability. Also It will be difficult to start the engine if at all. You can check the continuity of the two coils in the MAP (one coil is the two outside pins, the other coil is the two inner pins) but this test doesn't reveal anything if the diaphragm is torn.

Another concern is the Throttle Position Switch: if the PC board copper traces are worn you can get poor engine performance as you are describing. You can check if the TPS is the problem by disconnecting it and driving. If your problems disappear, you'll know it isn't the TPS.

As for trigger points about all you can do is borrow a set from SF Don and see if there is any improvement. I actually added a switch into one of the wires in the trigger circuit to see if I could replicate my hesitation problems but it wasn't definitive.
Good luck...D-Jet is great when it works ...but it is getting old, so don't sell your carburetors if you have them.

Yes, jetronic.org is a great resource, but I find that Volker is reluctant to impart too much of what he knows..

 

[sfdon]

“noticed that what I think are resistors, sitting just behind the brake vaccum booster cannnister, are not connected. There are several wires in this car under dash not connected so i never paid these any mind. However, if I understand some shop manual photo correctly, these are associated with the signal to the injectors. Is that what I am looking at here in the attached photo ?”

on a new car you would see into those plastic housings and know they are protecting spade connectors.

 

[neon]

Did you pin out the MPS?

sfdon - havent yet but will try, however i do not know where some of the paths lead due to the lack of a d-jet wiring diagram. Is there one on the site you can point out ?

Thanks
Dana

 

[neon]

Allow me to add a few things to SF Don's excellent suggestions. Having had problems with the MAP and Throttle Position Switch, I hope I can help. The main relay is located (usually) in front of the brake booster: there are two relays there, the one on the left is the main, the one on the right is the Cold Start relay. There is no separate relay that controls the injectors. If the Main relay is bad, you won't get power to the ECU via wires 16 (powers the computer) and 24 (powers the injectors.)


The MAP should hold a 15" vacuum for at least 10 seconds. If not, the copper diaphragm in the MAP is torn and the MAP will have to be rebuilt. A MAP with a torn diahragm makes the ECU think the engine wants to accelerate real fast and will dump a lot of gas into the engine ALL THE TIME...result, much smoke and poor driveability. Also It will be difficult to start the engine if at all. You can check the continuity of the two coils in the MAP (one coil is the two outside pins, the other coil is the two inner pins) but this test doesn't reveal anything if the diaphragm is torn.

Another concern is the Throttle Position Switch: if the PC board copper traces are worn you can get poor engine performance as you are describing. You can check if the TPS is the problem by disconnecting it and driving. If your problems disappear, you'll know it isn't the TPS.

As for trigger points about all you can do is borrow a set from SF Don and see if there is any improvement. I actually added a switch into one of the wires in the trigger circuit to see if I could replicate my hesitation problems but it wasn't definitive.
Good luck...D-Jet is great when it works ...but it is getting old, so don't sell your carburetors if you have them.

Yes, jetronic.org is a great resource, but I find that Volker is reluctant to impart too much of what he knows..

Hey Bill - thanks much for those suggestions. Yes I was planning on the vacuum test on the MAP. Interesting explanation. I did note some carbon on the plugs and there was a tendency to backfire a bit on deceleration but nothing remarkable. However I have no trigger signal at all to the injectors based on noid light testing.
On the relays, it looks like I have possible 3 relays grouped together right behind battery, I will send photo. Nonetheless I had power to wire 16 and 24 ap[prox 12 V at last check, I will recheck that.

Tough diagnostic exercise for a newbie

Still love that coupe !


Dana in CT