BX GTI Won't Start - Troubleshooting

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BXTASY
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BX GTI Won't Start - Troubleshooting

Post by BXTASY »

Howdy BXers - my ’88 GTi won’t start, after several years of renovation. No major engine work was done. The airflow meter/filter assembly was removed and re-installed.

Engine cranks, all instrument lights illuminate. New parts include battery, fuel filter, coil, distributor cap and rotor, ignition wires, spark plugs. Plug firing test seemed to show spark, but it looked a bit weak in daylight.

Battery power through the connector reaches the junction box (black connector, Column V, Stage 4) and then to the ignition switch.

Fuel pump operates and appears to have adequate pressure to the rail.

Injectors tested good with a small electronic device. Used carb cleaner on each.

With power interrupted somewhere, injectors can’t be tested for power from the ECU.


Running diagnostic checks in Chapter 2 of the Service Manual:

1. The relay bracket has 7 relays, including those for the air conditioning. Are injection relay #731 and injector relay #734 on the rear positions on the engine side (right) of the bracket, or on the outer (left) side? If I’ve identified the correct ones on the bracket next to the battery (left side), they have different wiring colors than shown in the manuals.

BX Relays.jpg



#734 (as I’ve tentatively identified it on the outside of the bracket, aft position), has two blue, one yellow, one brown.

#731 has two blue, two green. That’s similar to #734 on Haynes wiring diagram 6, circuit V (page 13-50).

On the bracket inside:

Aft relay has 3 blue, 2 green.

Next to it, the relay has 2 yellow, 2 green.

On the Haynes diagram, some wires are shown with a bar above the color letter, indicating a stripe. However, none of the seven relays have wires with stripes.

2. At the top of the first graphic (Chapter 2, page 5), there is an instrument symbol next to the battery symbol - does this represent fuel tank level? Or power to the instrument panel? Or what?

BX Relays 731, 734.png


The ignition key symbol shows “M” for “Marche,” or ignition on, correct?

On the fuel pump illustration, what is the circular symbol showing “U = 12v”?

BX Fuel Pump Test.png


3. The third graphic (Chapter 2, page 6) shows the ignition key in the “D” for “Demarreur, or starter engaged, correct?

BX Relay-ECU Connector Test.png

I'd love to drive it to the West Coast Rendezvous in Pismo Beach! But I don't want to wait until September!

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Tim Leech
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Re: BX GTI Won't Start - Troubleshooting

Post by Tim Leech »

Have you checked the ignition amplifier in the bulkhead if you have a weak spark? And I take it the cam timing is correct.

You say have fuel to the rail so it’s either air or Ignition. Have you tried Sending some easy start down the intake as you crank?
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Kitch
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Re: BX GTI Won't Start - Troubleshooting

Post by Kitch »

Tim Leech wrote:
Thu Jun 04, 2020 10:10 am
Have you checked the ignition amplifier in the bulkhead if you have a weak spark? And I take it the cam timing is correct.

You say have fuel to the rail so it’s either air or Ignition. Have you tried Sending some easy start down the intake as you crank?
The amp is on his distributor Tim (you can see it on the picture :P )

Just because it's getting fuel to the rail, doesn't mean the injectors are firing. I don't know much about the GTi setup sadly, but if there is a crank sensor that'd be a good place to start. The amp as Tim says can also give grief.

As an aside, testing spark plugs in the open air doesn't always work, because if you have a weak spark, it may struggle to ignite under compression, but still manage in the open air. A better way is a spark plug tester (goes on spark plug between plug and HT lead). Even those aren't foolproof, as the plug could be breaking down internally and shorting to the head.
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Re: BX GTI Won't Start - Troubleshooting

Post by Kitch »

In answer to the questions:

1- No idea, I'm afraid. I've never had a BX with relays next to the battery! On the 16v, they're over by the offside suspension strut (the injection and fuel pump relays, anyway).

2 - The dial image with the battery next to it indicates the dials have power. Without seeing the rest of the manual for context, it may be an indication you have the ignition in the first position (i.e. so the battery lamp illuminates, but none of the gauges do). It's a test position, and subsequent diagrams will have the dials in a different state (e.g. full ignition or cranking)

3 - The timer with the 'U' next to it shows that you will only have 12v for a limited time at the fuel (the priming stage, effectively). I'm not sure what 'M' stands for, but this is the ignition position (as opposed to the first/accessory position). It means when you turn the key to the final click before cranking, the pump should receive 12v for a brief period of time. Not all cars do this (it depends on the design of the fuelling system), but in the case of the GTi, it does.

4 - Yes, I believe 'D' is the cranking position.
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David
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Re: BX GTI Won't Start - Troubleshooting

Post by David »

I had trouble getting a GTi engine going after it had been out of the car. It had a spark, the injectors had fuel but it wouldn't go. It turned out that a wire from the coil to the ECU to control the injectors was snapped and missing. Once they were connected together it fired up. I made a post on it at the time, it was around 2016. It describes where all the wires go and what they do. Maybe that same wire has corrosion on it if you've not disturbed it.

Does the rev counter jump up when cranking it? If not then it might be the coil or corrosion on the coil pins, if so then are the injectors opening? If so then it's probably losing spark instead. If not then I'd look at that wire.

Hope that helps.
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Re: BX GTI Won't Start - Troubleshooting

Post by prm-comp »

I would initially go with a possible fault on the CA sensor as Kitch mentioned. Also ECU cables/ connections.

With the ignition on, the ECU needs to see a voltage generated by the sensor while cranking
before it will fully activate both fuel and ignition operating systems.
To rule out any problem with this unit, first check the resistance. Depending on the brand, resistance should be somewhere between 350-550 ohms.
Remove the spark plugs and check the sensor output voltage while cranking, Again, depending on brand, voltage should be between 4-8 volts. Unsure?? of the minimum voltage required.

I hope I've got my figures right as Its sometime since I last owned a GTI !!!

Regards

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Re: BX GTI Won't Start - Troubleshooting

Post by Kaapelimies »

BXTASY wrote:
Tue Jun 02, 2020 7:10 pm
Howdy BXers - my ’88 GTi won’t start, after several years of renovation. No major engine work was done.
So you did not change the flywheel, even by incident :wink: :?:
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Re: BX GTI Won't Start - Troubleshooting

Post by Jaba »

This early GTi does not have a crank sensor. Timing is from the distributor position in the head and needs to be rotated to adjust.
The rev counter as Pete suggested is a good diagnostic tool. If there is no dial movement then there are no 12v ignition pulses. Its better to check this with plugs out for a few more revs.
And yes zee D meenz demarrer or start up with starter motor een French.
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