1985 vw quantum, bad relay or fuel pump?

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vayankee

Member - Posts: 28

Joined: September 04, 2011

Location: Virginia, United States

Posted: September 09, 2011 at 11:46 AM / IP Logged

howie ll wrote:

Here we go with the usual catch-all answer to VAG problems...POS engine management

I don't understand what you mean here.

howie ll

Pot Metal - Posts: 16,466

Joined: January 09, 2007

Location: United Kingdom

Posted: September 09, 2011 at 12:27 PM / IP Logged

Amongst other things the engine management units on VAG (=VW, Audi, Seat and Skoda) are a POS, they fail!

howie ll

Pot Metal - Posts: 16,466

Joined: January 09, 2007

Location: United Kingdom

Posted: September 09, 2011 at 12:28 PM / IP Logged

As do the factory immobilisers on mid-late 90s cars.

vayankee

Member - Posts: 28

Joined: September 04, 2011

Location: Virginia, United States

Posted: September 09, 2011 at 4:34 PM / IP Logged

howie ll wrote:

As do the factory immobilisers on mid-late 90s cars.

I agree that VAG stuff fails, but from my experience and that of other owners of Quantums, the ignition control moduel and the oxygen control modules on these cars are pretty good. They are not as complicated as other systems, I understand. And in this case, I suspect operator error: my miswiring or misconnecting or missing something wrong out of ignorance. That's why I wrote to this forum.

oldspark

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Joined: November 03, 2008

Location: Australia

Posted: September 13, 2011 at 3:57 AM / IP Logged

Hall/vane ign sensors "not as complex"... Oh I'm so glad I have a Jap reluctor system (and the Lucas Rita).

And spark sensing for fuel pump? By definition, that is complex. (As I wrote recently, it should be done by the ECU/EMS, not the relay.)

They should have used the carby system - eg: an alternator-(charge-light-)controlled SPDT relay with STARTER priming (via 87a) else charge-lamp via diode - and starter via diode - to energise a SPST relay. 2 diodes else extra mechanical contacts/switching instead of a spike-suppressed pulse sensor (ie, at least a capacitor else heating vane etc...).

Plus the power-on primer if required...

oldspark

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Joined: November 03, 2008

Location: Australia

Posted: September 13, 2011 at 4:11 AM / IP Logged

PS:

vayankee wrote:

awdeclipse wrote:

What about when you crank the engine, does the fuel pump turn back on?

>No, with the correct relay in place, it does not.

IMO the correct relay should pump when cranking - that is an essential part of fuel pump control - ie, it pumps when cranking and when the engine is running.

EFI systems (and some carby systems) also add the "pre-start" priming - ie, when the IGN is first turned on (pumps for up to a few seconds)

If your pump is NOT pumping with the CORRECT relay fitted, then the signal from the coil- is faulty, else that module in the relay is faulty.

If I misunderstand the operation of that relay, then fine. But in that case, what turns the pump on whilst cranking? For EFI, it MUST be pumping when cranking. (Carby systems may start without it.)

vayankee

Member - Posts: 28

Joined: September 04, 2011

Location: Virginia, United States

Posted: September 13, 2011 at 7:52 AM / IP Logged

oldspark wrote:

Hall/vane ign sensors "not as complex"... Oh I'm so glad I have a Jap reluctor system (and the Lucas Rita).

> Fortunately, I wrote "not as"; unfortunately, I did not write "compared to later VW engine management, namely, Motronic."

And spark sensing for fuel pump? By definition, that is complex. (As I wrote recently, it should be done by the ECU/EMS, not the relay.)

> I could but will not debate complexity theory with you, but I believe that you are right about the ECU's role. Actually, I suspect that the relay and the ECU are interconnected so both "control" (that culturally-loaded word) the spark sensing that takes place at the fuel pump.

>Since we last commented here, three experienced VW guys have pointed to the ECU as a source of the non-starting in my case. This is not to condemn the ECU as poorly designed, but I suspect as the result of my mistesting the fuel pump wiring, thereby blowing two good fuel pump relays and possibly my ECU, and maybe more stuff. Again fortunately, yesterday my VW mechanic loaned me 4 ecus off his shelf to try out. trying them out is my project for this morning.

Plus the power-on primer if required...

>I can't comment here, except to say that I hear NASCAR is going to move away from carburetors. As I said earlier, I am not a engineer, but I do value our environment, and if FI and ECU's are better at controlling pollution, I have to favor that solution. And speaking of carburetors, the last car I had with a carb was a 1980 FWD Subaru. That car did not want to do much in terms of high speed, so driving coast to coast back in 1988 was not exactly fun. I didn't expect anything from it after learning that the nothing could be done to to carb to enhance its capabilities. Again, from a non-engineer.

vayankee

Member - Posts: 28

Joined: September 04, 2011

Location: Virginia, United States

Posted: September 13, 2011 at 7:57 AM / IP Logged

oldspark wrote:

PS:

vayankee wrote:

awdeclipse wrote:

What about when you crank the engine, does the fuel pump turn back on?

>No, with the correct relay in place, it does not.

IMO the correct relay should pump when cranking - that is an essential part of fuel pump control - ie, it pumps when cranking and when the engine is running.

EFI systems (and some carby systems) also add the "pre-start" priming - ie, when the IGN is first turned on (pumps for up to a few seconds)

If your pump is NOT pumping with the CORRECT relay fitted, then the signal from the coil- is faulty, else that module in the relay is faulty.

Yes, it would seem that the pump should operate when the engine is cranking. But maybe there is a signal telling the pump not to work if the engine does not have spark. I'll check and let you know on this.

oldspark

Gold - Posts: 4,913

Joined: November 03, 2008

Location: Australia

Posted: September 14, 2011 at 3:26 AM / IP Logged

That relay only senses spark - not cranking.

So if no spark, you'll only get the initial power-up pumping for a few seconds.

PS - I missed the previous reply...

The complexity is simply the circuitry. Ignoring Power-On priming, the alternator & cranking version is merely 2 diodes plus the relay. Spark sensing requires more components and the same relay, hence more likely to fail. (Diodes are the most reliable solid-state device. Spark sensing involves capacitors which are more prone to failure, plus transistors which are diodes with a bit extra.)

Spark-sensing is used for total loss systems (battery only - no alternator) else as a redundancy for alternator or air-flap sensing.

The ECU isn't a bad design per se, I see it more of an oversight (though nothing beats Delco).

Other K-Jetronic vehicles use a spark-sensing relay so I suspect fuel-pump control is not included in the ECU (IMO that's strange since priming is essential to prevent injector damage etc).

But either the ECU controls the pump, else it doesn't. If there is ECU control, there should be no reason to use anything but an ordinary SPST relay.

And again, as I understand that KAE 3.300.210 relay (as per your other thread), it has internal circuitry for spark control (and presumably the power-on priming - ie, a power-on high for a few seconds). That is used INSTEAD of ECU control. It does not make sense that the 3.300.210 would be used if there was ECU control - ie, IMO it is intended for carby systems without an ECU (or early aftermarket ECU/EFI systems - ie, those with analog ECUs & pot adjustments etc).

If it were my car, I'd junk that relay and use an ordinary SPST relay with diodes from the alternator (regulator's charge light circuit) and cranking signal (ignoring its connections to the "voltage" relay). The power-on prime could be as simple as a capacitor, else an R + C delay with transistor or FET switching.

vayankee

Member - Posts: 28

Joined: September 04, 2011

Location: Virginia, United States

Posted: September 15, 2011 at 5:56 PM / IP Logged

oldspark wrote:

That relay only senses spark - not cranking.

So if no spark, you'll only get the initial power-up pumping for a few seconds.

PS - I missed the previous reply...

> I think I see your argument-keep it simple so less chance of failure. And that is what happened, though I was the cause of the failure. But on the other hand, I don't hear of a lot of failures. By that I mean, my mechanic and my Quantum owners' group would be quick to yell about something like this that gave out a great deal. Yes, the fuel pump relay of mine and others have quit, and it is inconvenient, but we are talking about cars that are about 20 years old with lots of miles, and usually are driven in tough conditions-daily drivers in northern climes.

Spark-sensing is used for total loss systems (battery only - no alternator) else as a redundancy for alternator or air-flap sensing.

The ECU isn't a bad design per se, I see it more of an oversight (though nothing beats Delco).

Other K-Jetronic vehicles use a spark-sensing relay so I suspect fuel-pump control is not included in the ECU (IMO that's strange since priming is essential to prevent injector damage etc).

> I don't understand why you and the other fellow use such strong language here. The ignition control unit in this system lasts a long time, gives great economy, has been very reliable. I again am not an engineer to criticize or praise how something is designed, but when results are favorable, how bad can it be?

But either the ECU controls the pump, else it doesn't. If there is ECU control, there should be no reason to use anything but an ordinary SPST relay.

>Again here, I can not comment, and I am sorry to say I will not be able to understand any technical insights on this point.

> You have made your point. but I think if you want to argue a point like this you should engage someone who is able to respond.

> I know you say "if it were my car," but that does not make your argument any stronger. In fact, it is a bit of an insult, when I don't have thetechnical wherewithal to argue with you.

I am sorry if I offend you, but this discussion seems to be to be getting out of hand. i did appreciate hearing from you on the basics of relays, but going beyond that into design changes that you feel so strongly about is worrisome to me.

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