Ok, we've tried everything, so I am resorting to the experts! Here's the situation: 1970 1800E. Car starts & runs fine. When the bright lights are flashed or engaged or disengaged, the car briefly sputters when the stalk is released.

Upon doing further diagnosis, it appears that the computer is instantaneously shutting down. The reason I say this is because with the car off, you can switch on the ignition and hear the fuel pump relay (and pump) turn on for approx 1-1.5 secs. Then, without starting the car, if you flash the bright lights, the pump relay and pump run again for 1-1.5 secs. As far as I can tell, this is the indication that the computer thinks that it has just been turned on, and it should "prime" the fuel pump.

We have tried everything, including checking the FI ground wires, separately powering the computer (bypassing relay), checking for momentary power drop in the feed line to the computer, even totally isolating all FI harness wires and only powering and grounding the computer. The result is the same - when bright light stalk is flashed, upon returning to the "home" position, the computer "resets" and pulses power to the pump relay for 1-1.5 secs.

I'm stumped, and will be headed back to Australia on Tuesday, so really hope somebody has the clue so I can help Dad get the car put back together by then! Thanks you guys, and feel free to e-mail Dad directly at garysievert@swbell.net if you can discuss/chat one-on-one.

Regards,

Greg Sievert

You might also want to check other ground connections. Bad grounds have a tendency to produce the strangest possible symptoms in seemingly unrelated circuits.

Thanks for the tip. I think we will double-check the computer ground. We made sure the headlight flasher switch was grounded, and also put a new ring terminal on the computer & other FI grounds on the intake manifold. We also ran a ground from there directly to the battery negative terminal - still no luck. I'm leaning now toward some sort of electromagnet interference because Dad has moved the computer from its original location that was somewhat isolated from other electrical circuits to an area under the dash where there are a lot of wires, new relays, etc. When we pulled the computer out and layed it on the driver's footwell, we could get the symptoms to go away if we moved the headlight flasher wire far away from the computer. When we brought the wire back close to the computer, the symptoms came back.....of course the elctrical interference could be exacerbated by a poor ground somewhere. We even grounded the computer case back to the neg terminal on the batt with jumper cables - that should be a good ground!

Greg

I'm leaning now toward some sort of electromagnet interference because Dad has moved the computer from its original location that was somewhat isolated from other electrical circuits to an area under the dash where there are a lot of wires, new relays, etc.

I have always found the position of the electronic control unit (ECU) strange - under the right hand front seat. Apparently there was enough room under the dash, otherwise your father wouldn't have been able to put it there. Volvo probably experienced similar problems when working on pre-production 1800Es.

It could also have something do to do with ageing electronic components. Semiconductors don't really age, but electrolytic capacitors (elco) do. When that happens the capacity of the elco decreases. That could affect EM-immunity.

I expect the signals from the various sensors to be weak compared to the strong current that the high beams draw. When you switch on or off a high current, it can cause a spark at the contacts. A spark causes radiowaves that could garble the small signals to the ECU. Moving the ECU away from the spark will make it less susceptible to its radiation.

Also, a relay has a coil that activates the contacts through magnetism. When you switch the relay on, a small current is flowing through the coil causing a large enough magnetic field to activate contacts. You probably know that a coil is an inductive load. And you may also know that disconnecting a current from an inductive load almost always causes a spark (the coil and contact breakers in the ignition system essentially do the same thing!). It strikes me that the interference only occurs when you switch OFF the high beams...
If you want to keep the ECU under the dash, try relocating the high beam relay.

Daily;

My compliments! You make some excellent points, which I have elaborated on in my post! Even the quality electrolytic caps which Bosch used in their FI comps may be showing signs of old age by now, and so experience electronics guys (like I expect you are!) could easily see this as being a cause of Gregs symptoms!

One thing I have to say about the under-seat location of the FI comp, is that I can understand it perfectly!...it's one of the best protected places in the vehicle, and out of the heat of the engine compartment...right under the passengers' butt, and more accessible than under the dash (although that location was also used)! In some formula race cars that's where the fuel cell is for the same reason...it may seem strange at first, but you want to protect the tank from damage only second to the driver (the fact that it is a big mass also makes it desirable to bring it as close to the CG as possible)!

Cheers

The "computer" in the 1970 1800E, and all 1800's with computers, is placed under the dash at the factory.

AYe - that's where the box is on my '71 1800E, asnd where it was on my '72 1800E. My 145E, however, had it under the seat.

Have you tried checking the voltage coming out of the relay and seeing what it does when you click the headlights on and off? I think both high an low beams are on momentarily when you pull the stalk back (although I may be thinking of a nother car) - perhaps this is dropping the voltage due to a bad battery, voltage regulator, or wiring connection.

The FI system gets its power directly from that positive battery terminal.

Well, I think this problem has us stumped and we're giving up! Not only is it the high-beams that cause the problem, but also switching almost any relay in the car. The computer is far away from the high-beam relay, so I find it hard to believe the relay itself is the cause - must be some inductive current loop throughout the body of the car or something. I have a feeling maybe the computer is degraded. Next step is trying it with a known good computer that I think Dad can get his hands on from a friend here in Houston. I've never wasted so much time trying to fix a problem without being able to find a solution!


Greg

Greg;

I have just started following this thread...Please confirm: The computer is hick-upping (probably reseting, or acting as if power has been momentarilly cycled) upon dropping power to any onboard relay...

If this is the case, it suggests that the spark created by the collaping mag field is affecting the FI computer in a nontypical way. Your FI comp MAY, for some reason (like a dried out electrolytic capacitor internally), be more suseptable to this type of spike...I propose a couple of tests to confirm this suseptability, and if you confirm this will have a couple of of solutions to propose.

Tests to try:

1. Using an oscilloscope if available, measure the magnitude of the (neg) voltage spike across the FI comp power connector (RIGHT AT the power connector) at relay turn-off.

If no scope is available, try connecting a "free-whelling diode" (type 1N4002, better yet, 1N5402) reverse polarized, across one relay coil to suppress the spike...does computer still hick-up? Try connecting clamping diode RIGHT at computer power input...repeat test. Try diodes at BOTH locations....repeat test. Try connecting an 1000uF 100V electrolytic capacitor (correctly polarized across the power terminals of the FI comp, RIGHT at the FI comp, (to do the filtering work of a nonfunctioning internal one)....repeat test.

Please advise results. Good Hunting!

Hi Ron - thanks for the information. Yes, it is a momentary hiccup when you flash the high-beam lights or with a couple other relays - including the A/C relays that are used with the Vintage Air system Dad has installed. I will be leaving to head back to AUS tomorrow so we will not have time to test your theories with the capacitors & diodes before I leave, but I will forward the info on to Dad's e-mail and maybe he can try it. I do believe your theory has a lot of merit, and I've convinced Dad to try a known good ECU to see if the problem still occurs. Unfortunately, many of the ECU's could suffer similar symptoms given they are all old. Funny thing is, most seem to be trouble free, so I am still wondering if there's some way that the circuitry that protects the computer could have been inadvertently damaged when Dad had some welding done on the car a while back.

Regards,

Greg

so I am still wondering if there's some way that the circuitry that protects the computer could have been inadvertently damaged when Dad had some welding done on the car a while back.

This is interesting information. The welding could have caused damage to the ECU if the battery ground lead was not disconnected before welding began. Even in my non-computerized Amazon I disconnect the ground lead before welding to protect the alternator's diodes from surges. There is one thing most semiconductors can't withstand, and that is a high voltage-surge (spike).

The metal case around the computer should shield it from any sort of electromagnetic disturbance. Sounds like you're having voltage spikes throughout the system when loads are thrown on. How new is the voltage regulator?

Well....the car is modified, so I can't say much except that he has a new alternator with internal regulator. I measured the computer supply voltage with a multimeter while the relay is being cycled - no blips or spikes that the analog multimeter can detect. I don't know if that is useful information however. I am leaning more and more towards a problem with the ECU itself. This could be confirmed I suppose with the detailed electronic tests provided in one of the answers received here (connecting diodes, capacitors etc) but I think we will just try it with another ECU.

Thanks!
Greg

Disconnect the throttle switch (ie the computer) and see how you car runs. The car should run fine (smoothly, consistently), but not be as powerful in acceleration etc. The computer was designed to increase/modify power, not supply it. If the car doesn't run fine with the switch unplugged your problem is NOT in the computer but elsewhere in the system.

well i am no expert but as far as i can tell the problem dove tails. either it's ur computerror or the problem is something else. try putting in a computer from a car that does not have this problem. if it still happens then it is less likely that you'll need to replace ur computer and more likely you'll need to replace a relay or something like that. but again i'm no expert, that's just something I would try.

Thanks Colin. Unfortunately Dad doesn't have a spare 1800E computer lying around. I do know now that it is something about the high-beam relay. I think its pulsing is causing electromagnetic interference with the computer, because moving the wire away from the computer eliminates the symptoms. We did try a different headlight relay (another used one) and it caused the same symptoms. When I hooked up a newer single relay, I couldn't replicate the symptoms. Of course the new relay wasn't made for hi-lo beams, so it doesn't have the see-saw action in it. Very strange....

Greg

Hi,
I have a bosch remanufactured ECU for 70-71 purchased in 1998, but sat in parts car. Let me know if intersted. Anyone have an idea what the going rate for these are? I also have another pulled from a parts car that was claimed to be original, and working.

cgj@rmi.net

Carl

Carl,

Your post seems to indicate that one ECU covered both years. I'm not certain, but I don't think that's the case.

After seeing the original post of this thread, I contacted Gary. I was ready for a little drive, and had heard about Gary's very nice 1800's, so, to help him in his attempt to diagnose the problem, and in trade for some very nice parts for my '72 ES, I provided an ECU from my '70 E parts car.

But when Gary checked the part number on the ECU in his parts catologue, it showed to be an ECU from a '71, rather than a '70. Two different part numbers

I'm checking to see if the one I provided somehow got switched with one from a couple of '71's that were aquired at the same time, but it WOULD help Gary, if the same ECU covered '70 and '71. That's why I'm asking for clarification.

gary

They are both CU25X computers and should work for both years. What is the P/N in question?

You can cofirm this yourself on the Bosch Site

http://www.boschusa.com/AutoParts/PartFinder/partfinder.asp

Greg
1970 1800e

Greg,

Here's the message Gary Sievert sent after he had a chance to look at the ECU that I brought to him. He needs the '70 E ECU. The one I brought to him was from a '70 E that "should" have been original to the car, but lots of things can happen in 34 years.

Frustrating, to say the least.

> > --- Gary Sievert wrote:
> Gary,
> Turned out the ECU I got from you was from '71 1800E not a '70.
>They are different.

>Do you have one from a '70?
>The Bosch # on the '70 ECU is 0 280 000 009
>the Bosch # on the '71 ECU is 0 280 000 017.
>The Bosch # on the '72 and '73 ECU is 0 280 000 034

gary

I think what I am saying is the two years do have different part numbers but they are both concidered CU25X units by Bosch so they should be compatable. I do not think I would put an 034 in.

Greg

It's extremely likely the '71 ECU is an improved version of the '70 box, and would work fine. There's no functional difference between the '70 and '71 motors, AFAIK.