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98 tdi 110 starting "issues"

3664 Views 7 Replies 3 Participants Last post by  chittychittybangbang
Hey all, I need some help
Recently got my first VAG, a seat toledo tdi. 1998 110hp version. It was great for the first two weeks then developed a starting problem. Cranks but won't fire.
Changed fuel stop solenoid, no joy, removed fuel stop solenoid and blanked off (just in case), still no luck.
Replaced fuel stop solenoid, then noticed that after leaving ignition on for anything up to 12 minutes, the fuel pump would suddenly clunk and the car would start and run fine. As the fuel pump clunked the glow plug light momentarily came on. Kind of indicated a power issue so relay 109 was replaced with a brand new unit.
Still the same problem, have to wait anything up to 40 minutes with ignition on before the glow plug flash indicating that all is well and the car will start. Unfortunately today it only managed 2 miles then cut out (first time i'd experienced this as usually once it started it was as good as gold and could be turned off and instantly restarted without issue).
The relay 109 stayed energised (audible click and can feel the changeover with my hand on it) while the fuel pump and glow plug light went mental, pulsing on and off. would crank and fire if you were lucky enough to coincide a crank between the spaz attacks but would only be useful for a few seconds before the next attack killed it.
Eventually the battery went flat after half an hour of attempting a useful amount of running time and only about 20 metres of movement.
Thats where I'm up to right now, AA had a look, and after refusing to believe everything i'd done and redoing the obvious (fuel stop solenoid, extra 12v feed to relay 109 to energise, ecu has power, no dash faults at all) towed it home. I need help.
I have no manual or wiring diagrams, only just found out that it's based on a mk4 golf (a big thankyou to this website as noone else has given me even that much information). I'm going to try to locate and pull the ecu tomorrow (water in wiring?) but does anyone have a wiring diagram or any more ideas.
I wonder if i supply a separate 12v and gnd to the fuel pump would that be enough, need to know the pinouts on the connector to the fuel pump. That won't help the glow plug light which might be an indication that the ecu outputs are all disabled until then. I don't know what is controlled when and what else (that I can't see) is also changing state at the same time as the pump and lights.
Obviously all the components can and do work as when it eventually allows it to fire it drives really well and pulls fine, til it now cuts back out again. But it means it's not missing, not down on power, it's not even unhealthily noisy.
Any suggestions welcomed, many thanks
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Make sure the anti shudder valve is open, if your car has one. It's vacuum controlled and looks like a throttle on the intake manifold. The solenoid could be telling it to close. Or maybe it's sticking closed. Check all the grounds. Due to the intermittent nature and symptoms, it's not the timing belt.

It's not the glow plugs but you say the glow plug light is pulsing on and off while you try to start it? If so, that indicates a relay 109 problem. But since you've already checked it and replaced it, it sounds like there is some other problem that is causing a power fault to the ECU. Check the battery cables and other wiring for corrosion. Maybe the ecu is sitting in a pool of water?

If you want to trace the wiring diagram, get the factory service manual. There were year to year changes and I would not be surprised if your seat was also different.

Maybe someone else can chime in who had a similar problem but it sounds like an electrical problem related to ECU power if the glow plug and fuel pump are pulsing on and off. Remember that the fuel pump is electronically controlled, there is more than just 12v and ground to run it. It's possible that the ecu is bad but this is rare.
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For a 1998 you probably will not have an immobilizer so you can just plug-play. I'm not sure though because North America did not have immobilizer 1. Europe did. If your key has a small F on the blade, it probably does have an immobilizer. There is no specific coding as long as the part number is correct and from the same type of car.

Your local junkyard probably can tell you more since they have to know parts compatibility.
If there is no immobilizer light there is no immobilizer. It could just not be lit but they are normally lit when you turn the key on and go out within s a second.
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