No start '88 -- 9.5 VDC at coil in start mode? Ideas?

[Bob Prosser]

Need some input please regarding a sudden-no-start problem with my '88 Carrera daily driver (w/180K miles, well maintained, normally stone-reliable).

About a month ago, it would occasionally stall on me in the driveway or parking lot. When I hit the key again it'd spin, but there was nothing ... not even a sputter. Then less than a minute later it would start and run as though nothing had happened. Until next time it happened, which would be a week or so later. At that time, I replaced the DME relay, and the fuel pump (FYI, 100,000 miles ago, I updated the head temperature sensor to the two-wire version).

For the next ten days the car ran perfectly -- until this week: on Monday it ran fine. It sat until Wednesday evening, when I got in, hit the starter, and it spun but there was no fire -- not even a sputter. This time it has stayed this way -- it hasn't started since.

I smell fuel in the exhaust pipe, so I assume the fuel pump is working. I've looked at the grounds on and under the engine. This has always been a California car, and there is very little schmutz / corrosion on any of the contact points.

Also, with the ignition turned to the accessories position, I get 12.5 VDC at the coil, but when the switch is turned to the START position (engine turning over), voltage at the coil drops to 9.5 VDC. Is this drop normal, or does it indicate a bad ignition switch or DME ... I assume it's normal.

Reading through the threads, I have found that people with same year cars (‘87-‘89) with the exact same symptom (running one day, dead the next), have found the problem to be one of the following:

1. Failed solder joints on the DME board.
2. Bad ignition switch.
3. Failed flywheel speed sensor(s) or wiring connection at engine.

Thanks guys!
Bob

[techman1]

Give a close look to the battery- charge level, cable connections.
Have someone put a meter on the posts and watch the voltage as you crank.

[Bob Prosser]

Thanks. The battery is on a charger. Terminals are clean, tight. Battery is < a year old. Engine spins fast.

[Tim L]

Check the resistance of the speed and reference sensors

[Bob Prosser]

This is what I am about to do -- tell me if I am wrong:

1. detach sensor electrical connectors located on the left side of the engine

2. check the resistance when the engine is at room temperature (~25C or ~75F)

3. assume the following:

terminal 3 is the top pin in each respective connector (terminal 2 is center pin)

The resistance between terminal 1 and 2 should be ~ 960 ohms
The resistance between terminal 1 and 3 should be >100,000 ohms
The resistance between terminal 2 and 3 should be > 100,000 ohms

[Tim L]

That looks correct

[tkosier]

I'm in the same spot with my 150k miles '88. Not my daily driver so will wait until this weekend. Local friend and p car wrench said it may be the speed or reference sensor.
Good luck and keep posting!
Tom

[techman1]

Bob,

The reason I said check the connection at the battery: My wifes car, trouble starting, would turnover, just not catch. Measured voltage through plug in meter and voltage really dropped when cranking. Battery posts and cables cleaned, no problems!

[Bob Prosser]

I just tested the sensors ... three times. Here are my findings.

SPEED SENSOR (middle plug -- top being the head temp sensor)

Reading on the pin side of the plug (to flywheel):
1.) The resistance between 1-2 should be ~ 960 ohms
Reading 1-2 = .996 KΩ
2.) The resistance between 1-3 should be >100,000 ohms
Reading 1-3 = 0 KΩ
3.) The resistance between 2-3 should be > 100,000 ohms
Reading 2-3 = 0 KΩ

----------------------------------------------------

REFERENCE MARK SENSOR (bottom plug)

Reading on the pin side of the plug (to flywheel):
1.) The resistance between 1-2 should be ~ 960 ohms
Reading 1-2 = 1.004 KΩ
2.) The resistance between 1-3 should be >100,000 ohms
Reading 1-3 = 0 KΩ
3.) The resistance between 2-3 should be > 100,000 ohms
Reading 2-3 = 0 KΩ

The 0 KΩ readings seems odd to me (is it zero or infinity?) -- it's doubtful both sensors would fail at the same time. Also, I noted that the black rubber/plastic jacket on the wires crumble at the touch. Time for new, no question.

And, can anyone point me toward a thread showing how to replace the sensors? I have looked around, and find lots of reference, but no how-to (hopefully with photos). If there isn't one, then I guess it's time to make one.

[tkosier]

Try this:
no-spark problem finally resolved

Tom

[Wil Ferch]

What is standby battery voltage?...12.6 ?

[Bob Prosser]

Tom, thanks for the link. This is perfect. Seems the author of that thread found the same curious issue, i.e. infinite ohm readings on both sensors -- not just one.

Will, the battery is reading 12.48 VDC -- that's after hitting the starter/spinning the engine a few times.

[Tim L]

Seems the author of that thread found the same curious issue, i.e. infinite ohm readings on both sensors -- not just one.

2.) The resistance between 1-3 should be >100,000 ohms
Reading 1-3 = 0 KΩ
3.) The resistance between 2-3 should be > 100,000 ohms
Reading 2-3 = 0 KΩ

Just to be clear you reported 0 ohms not infinite, infinite between 1-3 and 2-3 is Ok

[rick-l]

Did the meter say OL or 0?

[Bob Prosser]

Thanks for asking. When testing 1-3 and 2-3 with my digital multimeter, I get a flashing "1.000 KΩ," and my manual says that means "out of range" (assume that means infinity?).

When testing the same with my analog multimeter, the needle moves slightly off the stop.

So perhaps the two sensors are/were within range? That said, the rubber insulator jacket on both had completely deteriorated, e.g., one touch, and it crumbled away, exposing the ground sheathing, so I am replacing with new today. Thankfully, they came out of their mount without a problem (first sprayed with WD40), so if the new ones are exactly the same dimension as the old, I will not have to make the 0.08 mm adjustment.



If the car doesn't start after this, I suppose I will start looking for cold solder joints in the DME box. Ideas are welcome. Thanks.

[911pcars]

As far as system voltage goes during engine cranking, 9.5 V sounds normal for a fully charged battery. The reduced voltage is due to the current requirements of the starter motor (normal voltage drop).

With a voltmeter, you can measure voltage anywhere in the system during cranking, and it will be the same (try directly at the battery to prove it). This is why, on many vehicles, the headlight and accessory circuits are temporarily bypassed during cranking so as to provide optimum voltage for the starter motor.

If system voltage during cranking falls below 9 volts, the battery is partially discharged or not up to spec, or the starting circuit is compromised (loose, corroded connections, etc.)

Thus: Sounds like available source voltage is okay. The engine needs air, fuel and spark. Go through the check list and inspect if you have enough of the above and at the right time. The easy stuff first (spark at plugs, DME box makes usual noise, etc.).

Sherwood

[Bob Prosser]

Sherwood, thank you for your input. (What's this about DME box making noises? Were you referring to the fuel pump by chance?)

I will look over the DME box's solder joints next, but think I should first wait to install the new sensors. One thing at a time. : )

[911pcars]

Originally Posted by Bob Prosser

Sherwood, thank you for your input. (What's this about DME box making noises? Were you referring to the fuel pump by chance?)

I will look over the DME box's solder joints next, but think I should first wait to install the new sensors. One thing at a time. : )

I may have mis-spoken. Not sure the DME makes any audible operational sounds like a CD box.

Sherwood

[Bob Prosser]

Guys, here's where I am today:

- new DME relay
- new fuel pump
- new flywheel speed sensors
- updated head temp sensor (done years ago)
- 12.5 VDC at the coil, with 9.5 VDC while cranking over

And, while cranking the engine, and a spark plug held against the intake plenum's ground bolt, I see no spark. I also smell gasoline coming from the tail pipe (should I assume the fuel pump, and injectors are working properly?)

Next stop, unless you guys have ideas, is to double-check the DME relay, and then pull out the DME box, and start looking for issues, per other threads on this list.

Your input is always welcome!

[techman1]

Bob,

Have you checked the interior of the Dist. Cap and rotor?