No start sanity check (Problem Solved)

[P.Muck]

Let me start off saying that I have searched and gotten a wealth of info from the forum to help me so far, but I want to confirm my current assumptions before I start buying parts...

I have an 86 325es that for the past month or so has had an issue with the tach reading too-low RPM (i.e. should be around 3k, displays ~2k). I assumed I had an engine speed sensor going bad (not gauge or ground- related), since my OBC was also suddenly claiming I was getting >34mpg over the past three tanks of gas. (actually closer to 26) This may or may not be related to my current problem..

Other than that, it's been running great all summer long until yesterday. Now it cranks but won't start.

The first thing i did was check that the Engine speed sensor and Reference sensor inputs at the DME- both read around 1K ohms.

• I confirmed that I have fuel, but no spark as per bentley test procedures.
• Checked all power and grounds to the DME as per the bentley and everything reads good
• Measurements at the coil are within spec. (primary res =.7ohms, secondary= 5.6K)
• Cam is turning so I'm ruling out timing belt.

My next steps are to see if I'm actually getting pulses from the speed and ref sensors, and if so, try to find a replacement DME.(anyone have an 027 for sale?)

My questions are:
1. would I still get fuel without the engine speed pulse?
2. what if I'm not getting a pulse from the flywheel? How much of a pain is that going to be to fix?

Sorry for the long post and thanks in advance.

Pat

[SmokeE30]

fuel pump receives it signal from the crank position sensor so if you have fuel i would think the cps is not you issue. however if your cps is bad i have a set of e sensors laying around if you need them

edit:

credit for this goes to jlevie but its a great bit of information to help with a no start

For the engine to run the following conditions must be met:

Power on DME pins:
27 Start Input
18 Un-switched Power input
37 Power Input from Main Relay

Ground on DME pins 2, 14, 19, 24

Timing data from the CPS on DME pins 47 & 48 from a rotating engine

To have spark power must be present at the coil positive and ground pulses
from the DME's pin 1 must reach the coil negative. Power to the coil is
controlled by the ignition switch via C101. When checking for spark, use the
output lead from the coil to eliminate the distributor, rotor and plug wires.

To have injector firing power must be present at each injector and ground
pulses from the DME's pin 16 (Bank1) and pin 17 (Bank2) must reach the
respective injector bank. Note that the injectors are wired as two banks of
three. With cylinder 1,3,5 being bank 1 and 2,4,6 being bank 2. Power to the
injectors is controlled by the main relay. Injector firing is best checked
with a noid light.

The fuel pump relay must have power on pin 86 (relay coil) from the main relay
output (pin 87) and power on pin 30. The DME will ground pin 85 to turn on the
relay and power the pump(s) via pin 87. Of the above, only the fuel pump power
is fused. So if the there's power at pin 87, but not at the pump, check fuse
11.

The main relay and DME pin 18 receive power from the smaller of the two wires
that connect to the battery's positive terminal. That wire incorporates an
in-line fuse. When the DME is presented with a start signal, it grounds the
main relay pin 85 and furnishes power to the fuel pump relay, injectors, and
DME.

Troubleshooting:

Disconnect the battery and the DME cable. Then:

1) Disconnect the coil negative and check continuity from that connector to
DME pin 1. Also verify that from DME pin 1 to ground is an open circuit.

2) Check the resistance across DME 47 & 48, which should be 500-560 ohms. If
the CPS is dismounted, the resistance can be seen to change from about 500 to
540-560 ohms when a ferrous object is brought to the face of the
sensor. Neither pin should be grounded.

3) Check for continuity from DME 36 to main relay 85 and from DME 3 to fuel
pump relay 85.

Reconnect the coil, remount the CPS (air gap should be 1mm), plug the
relays back in, reconnect the DME, and connect the battery. Then do the
following checks:

1) With the key off, verify that power is present at DME pin 18 and main relay
86 & 30.

2) With the key on, verify that power is present at DME pin 27 and pin
18. Power to pin 18 is from the main relay and there should be power to the
injectors and fuel pump relay.

3) With the key on, verify that no voltage is present at the DME grounds (2,
14, 19, 24).

4) Verify that power is present at the coil positive and at fuel pump relay
pin 30. Those get switched power from the ignition switch via C101.

The engine will start and run (if poorly) with only those connections to the
DME in place. The other signals from Cylinder ID, AFM, temp sensor, etc., are
necessary for proper operation. But they won't prevent the engine from firing.

IMPORTANT:

A power check means seeing a voltage within about a tenth of a volt of what
you measure across the battery terminals, which should be at least 12.6v on a
charged battery.

A continuity check means seeing less that 1 ohm of resistance.

An open circuit means seeing a resistance of at least 100k ohms.

A good quality auto-ranging digital multimeter will make these tests much
easier.

[SirWolfian]

Did you change the sensors that go in the bellhousing of the transmission?

NVM I just read that you checked them, I had the same problem on my 86 325e the sensors read 1k ohms but they were damaged internally, so I changed them and re installed them, so now the car starts properly

And I might have a spare 325e spare ECU I'll have to check

[P.Muck]

Thanks for the replies guys...
SmokeE30, I think most of the DME pin #s you refer to are for an i engine, not Eta, but I have basically followed these steps to this point.

Sirwolfian, when you had the problem with the sensors, did you have fuel but no spark?

I can't seem to find a conclusive answer to this. Hopefully tonight I'll get a chance to visually check the sensors and see if they are responding to a ferrous object

Thanks again,
Pat

[SirWolfian]

Thanks for the replies guys...
SmokeE30, I think most of the DME pin #s you refer to are for an i engine, not Eta, but I have basically followed these steps to this point.

Sirwolfian, when you had the problem with the sensors, did you have fuel but no spark?

I can't seem to find a conclusive answer to this. Hopefully tonight I'll get a chance to visually check the sensors and see if they are responding to a ferrous object

Thanks again,
Pat

Yeah, when I had the problem the injectors and everything in the fuel system worked perfectly but we had no spark all but 1 or 2 cylinders, We changed both sensors with new ones put some more gas in the tank, re installed the sparkplugs, and then we cranked her up and she started

[P.Muck]

I pulled the Reference sensor and engine speed sensors last night and confirmed that the resistance fluctuates when I put a metal object up to them. Seems like that should rule those out. (Actually I think the fact I have fuel when cranking should rule them out, but I can't confirm that.)
So now I'm back to no spark...
All power and grounds confirmed at DME
Confirmed cam is moving
Power at coil
Coil resistance is OK

I guess my next step is check dist cap and rotor while waiting for a spare DME to show up...

Anyone have any other suggestions?

Thanks,
Pat

[P.Muck]

So even though I have all power and grounds at the DME, I don't hear the buzzing or humming that has been described in other no start threads with the key in start.
Anybody have any tips?

[jlevie]

If the ICV doesn't vibrate with the ignition on and you don't have spark or fuel pump operation when cranking there's a good chance that the DME isn't running. The main relay, fusible link, or ignition circuit would be obvious candidates.

[P.Muck]

The ICV is vibrating, and I get fuel at the rail when cranking. I'm not getting any spark though. I've swapped in a known good coil and replaced the cap and rotor. I can feel the main relay clicking when I turn IG on.

[jlevie]

When the ignition is on, is there power at the coil positive post? And are you checking for spark at the coil output lead?

[P.Muck]

I have battery voltage at the coil with ignition on. There's no spark at the coil output lead.

[jlevie]

I'm not sure which of the timing sensors turns on the fuel pump relay, but both need to work to have spark. Before I tried a different DME I'd replace both sensors with new OE parts and make sure they are correctly connected. While the sensors were out I'd make sure that the timing slug is still on the flywheel.

Sensors can ohm out okay and respond to a ferrous object and still be bad.

[P.Muck]

I swapped the sensors tonight and still have fuel but no spark.
How can I rotate the flywheel to check for the slug? I tried spinning through the hole for the top sensor, but couldn't get a good grip with my screwdriver.

By the way Jim, thanks for your advice with this. It's much appreciated.

[Bretts85E30]

Ur gonna need a 2nd person cuz I've personally done this and just have em rotate the engine at the crank pulley with a 22mm wrench while ur under the car watching through the hole for the pickup I've had my pickup break twice had a steel shield fabbed up after the 2nd time

[dsphil]

I am at the exact same boat here. I did everything P.Muck did. I also checked the power at the key ignition, c200, and c101.
I'm waiting for the 2nd person to show up to crank the pulley too. The funny thing is that it will starts whenever it wants to. The first scenerio started very rich and low idle at cold engine (bouncing 300-350). If I don't open the throttle it will stall. The second scenerio will not start at all no matter what. the third is it will start and stay running until I shut it off. All these in the past month.