Gtaebr

Dean read Hiltons post bottom page 1 seems to make sense given the symptoms.

Hilton

Did you already check the ignition monitoring relay for a green or red LED? Did you try bridging the 3 pins of the relay to see if its the ignition monitoring system thats at fault? That would be the first thing to check if you haven't.

Re-reading my earlier post I still think O2 sensor or sensor harness damage is a possible cause for your no-start. The sensor harness will fray and short on the heat shields or itself.

For the O2 sensor, you can test it relatively easily. If you unplug the O2 sensor in the passenger footwell, then disconnect and re-connect the battery, and then try starting the car, what happens?

Assuming the fault is beyond the O2 sensor plug, disconnecting the battery will reset the O2 adaption parameters - so the car should run ok for a couple of minutes until it warms up and goes closed-loop, at which point the lack of a sensor will mean it gets a hunting idle and stalls as the revs drop too much.

If, after the above two tests of the ignition monitoring relay and the O2 sensor, it still won't start, I'd be using a multimeter on the LH harness, including checking both injector banks against ground at the LH harness, and the O2 sensor connector pins to LH connector too.

Dean_Fuller

Okay...all the O2 wires looked okay. So I went back to the panel. Anything to do with fuel I pulled and swapped out. Relay XXV is LH-Jetronic Fuel Injection. I swapped it out with a KNOWN good relay. The car STARTED...and is still running and starting. So...when this relay fails does what happens????? Does it dump fuel??? Because remember when I pulled the fuel pump relay the car would start and run out of fuel. Did I find the problem or is it just working FOR NOW?

worf928

My guess would that it is running for now. Further, my guess is that you have an intermittent short to ground between the injectors and the LH ECU. Here's why:

Power to the injectors is routed from the battery through the passenger compartment to the CEL panel through the relay, through the IMS relay then to the two branches of the injectors. (And the o2 sensor gets in there too.) The injectors fire when they are grounded through the LH via its ground that goes back to the left-side of the block at the rear under the pressure dampener. (Trace the wiring diagrams to see for yourself but don't believe them when they tell you that the injector ground is on the right side of the block.)

A common LH failure mode is that it always grounds the injectors, or grounds them cyclically on its own, out of sync with the rate of the spark (the famous injectors clicking all the time symptom.) Yours will run (for a time) without the relay but won't with the relay. That smells, not only of fuel but also, like the injectors are continuously grounded and allowing fuel to pass if there is fuel pressure.

You can test this theory with your multimeter. Remember that the injectors are arranged in two circuits (1,4,6,7 and 2,3,5,8). Knowing if one or both sets are locked open may help you find the issue if it is, in fact, a ground short.

Note that if the injectors are continuously grounded then the issue cannot be the FP relay or the IMS relay. It can't be on the 12v side of the circuit. It can only be between the LH ECU's ground, the LH ECU and the injectors.

HTH.

Dean_Fuller

Dave...Thats a lot of good info. You lost me on the last part though. I have never been comfortable with wiring...I need to learn but don't really know how out here by myself.

So I need to clean the block grounds...I have not don't that nor do I even know what they look like or where they would be. I will look into that.

Mrmerlin

remove the aircleaner base and look under the rear fuel damper on the left side you will see 2 sets of brown wires connected to a metal bar these are the grounds

Dean_Fuller

Thanks Merlin...I will clean those tomorrow.

worf928

Umm.. no. Probably not. Let me try this a different way...

Constant power to the injectors does not cause them to open/fire and pass fuel. When they are powered on one pin and grounded on the other they open and allow fuel to pass if there is fuel pressure in the rails. The LH grounds the injectors for very short periods of time with the periods and duration of ground timed to the engine speed and load (called pulse frequency and pulse width.) When the LH and the harness are doing what they should, the injectors are grounded intermittently through the LH. So, a dirty ground, or an intermittent ground of the LH would not allow the injectors to open if they have power.

However, a constant ground connection that bypasses the LH's internal timed/pulsed ground would keep the injectors open and flood the engine thereby preventing the engine from starting. If you have this (bad) constant ground connection, if you pull the FP relay there is NO power to the injectors and they stay closed. However, if you've recently tried to crank the engine with the FP relay plugged in and have flooded the motor with fuel, there is enough residual fuel in the intake manifold to allow the engine to run for a few seconds.

So, if you have a bad ground between the LH and its ground point the injectors will not open enough. If you have a ground connection between the injectors and the LH then the injectors will open too much. This latter symptom is also caused, sometimes, by a dead LH which is why your LH was the original suspect. You need to check and see if the injectors are always grounded when powered or if they are being "cycled" to ground by the LH.

The first thing to do is to figure out IF you have this suspect constant ground short that bypasses the LH's ground.

Get a cheap analog needle-type multimeter. Then:

With the FP fuse and relay in along with the IMS relay
1) unplug one injector
2) turn on the ignition
3) use the multimeter to figure out which injector harness plug pin is 12v.
the other pin is the ground side.

4) Put the meter in resistance or continuity mode(*) and see if you have 0 resistance or continuity from the ground pin of the injector plug to a ground point (cross brace bolts will work.)

- if you have 0 resistance then you have a short to ground
- if you don't, then do the above check on an injector on the other circuit (see previous post.)

IF you have infinite resistance (or no continuity) then you don't have the problem I'm describing, but see the last paragraph below.

(*) Continuity mode is just checking to see if the circuit is complete. For instance, you will have continuity between both ends of the battery ground strap or from one ground point to another, or from the jump post to the battery positive. 0 Ohms resistance (or less than 1 Ohm) is the same as having continuity. Infinite resistance means that there is no electrical connection between the two points you are testing with the meter.

Properly, the ground pin of the injector plug should have infinite resistance unless the LH is grounding it. The other should have constant 12v if the ignition is on (and the power side of the circuit is OK.) If you find that you do have infinite resistance on the ground pin, then get your helper to crank the engine while you check the ground pin. The analog meter - in voltage mode with a probe on each of the injector plug pins - should bounce back and forth between 12v and 0v if the circuit is OK when the engine is running or cranking.

An oscilloscope is a better tool for this, but, my bet is that you don't have one?

Mrmerlin

Dave thats some great info on testing,
IDK if you read this but the computers were checked, and came back as good.

Now in the mantra of JB Relay Relay Relay might this not be the path to follow.
Its quite possible that the relay that was swapped out is in fact now working as it should and so is the rest of the system.
As far as relays go i would open the removed relay and smell it ,
look on the bottom for melted contacts at the pins,
also then you can test the relay to see if 12v will close it,
and inspect the contacts for corrosion

SteveG

Thanks Dave for the explanation;
I'm just following and taking notes, but the above post sounds impossible. If the statement is true, and the relay is out, I'm wondering how the FP is being energized?

There are other grounds besides under the air box that can cause a no start.

Dean_Fuller

If you remove the relay to the fuel pump the car will run UNTIL the fuel in the lines and rails are spent. Then it will run out of gas. I have always done this if you need to remove a fuel line as it eliminates the fuel pressure.

So in short the fuel pump IS NOT energized but there is still pressure and fuel to burn...at least for a few seconds.

depami

How much time between "pull the relay" and "fires right up"?

If it were flooded, I wouldn't think it would "fire right up" without alot of cranking.

theshow72

I had a similar problem and solution on my 82. I replaced the fuel screen, fuel pump, fuel filter, fuel pump relay and fuel injection relay. The pump would run, there was plenty of pressure, but the car would not start. If I let it sit for a few seconds after trying to start it and turned the key it would start and run for a few seconds and then die. I though my L-Jetronic computer was dead. It turns out the new fuel injection relay was not the right one. I put the old one back in and it fired right up. I had been pulling my hair out cleaning grounds and all the other suggestions, but I had put in/purchased the wrong replacement relay.

worf928

Yeah. I read that.

There are a lot of possibilities. There could be multiple problems convolving the solution space.

The bottom line is that something's messing with the injectors. Diagnosing the problem needs to start with metered or scoped observation of what's happening on the hot-side and ground-side of the injector harness plug pins. Knowing if it's screwed-up power or screwed-up ground will cut the solution space in half.

A meter and/or scope and a 'noid light are the tools needed to start diagnosing.

It may sound impossible, but it is absolutely possible. Dean provided a differently-worded explanation from mine. I have observed the exact symptoms Dean reports on two occasions both times due to the LH being dead. BUT, a dead LH is not the only thing that could cause these symptoms.

Again, the bottom line is getting data. It's perfectly ok to throw new relays at the problem and to clean grounds. The relays are probably all old and nearing end-of-life anyway and cleaning grounds never hurts. But, that approach requires luck; resolution of the issue is based upon pure chance.

EDIT: As per the above, the wrong kind of LH relay might be able to cause the problem. The LH relay is a normal "53" relay.

Dean_Fuller

Problem arose again this last week. Several days of NO START. Pulled the fuel pump relay and it started. Replaced relay and car started but smoked BADLY. Black and gray smoke. Smoke from passenger side motor as well. Sounded and ran like it was running on just the driver bank of injectors. After about 3 minutes...as I was standing there looking. It just started to run PERFECTLY. Smoke went away just like that and motor smoothed out within a second or 2. So I will track the issue I have on the passenger side injectors. Just thought I would add to this tread so it will help ME and others later.