Bosch Jetronic LE3 info (gti 8v)

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rutter123
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Bosch Jetronic LE3 info (gti 8v)

Post by rutter123 » Tue Feb 17, 2015 6:12 pm

Does anyone know of a good source of test procedures/fault finding info for this unit, any links would be good.

The problem child Gti still running of a sort but still not right below 3000rpm have changed plugs, leads, diz cap and arm, new vac advance unit, new fuel pump and filter, new fuel lines, new pressure reg, injectors ASNU cleaned, new temp sensor, new tps, new coil and king lead, there are no air leaks, tried a different airflow meter to no avail, timing set at 5 deg btdc, engine wiring loom removed and checked for bad terminals, rewired injectors, relays all good, but the prob persists, idles nice at 900 rpm, but try to pull away and it hesitates, coughs splutters, tries to stall, seems to run fine above 3000rpm or is it? Plugs 1 and 3 seem to be running a bit leaner than 2 and 4? Sitting in traffic is a nitemare, its a fine balance of rpm's and clutch control just to pull away, no overheating issues and just dosent seem as lively on acceleration, i would say no quicker than my t/d, there is obviously some underlying prob but just cant get there, is returning about 30/35 mpg which i guess is about right, fuel pressure is ok at about 40/42psi.

Any suggestions out there?

After reading up it seems 205's suffered from the same probs with this le3 set up.
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sdelasal
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Re: Bosch Jetronic LE3 info (gti 8v)

Post by sdelasal » Tue Feb 17, 2015 6:46 pm

Do you have access to a good old fashioned vacuum gauge that you connect to intake manifold? Although you say no air leaks, the symptoms to me suggest otherwise!

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Re: Bosch Jetronic LE3 info (gti 8v)

Post by Tinkley » Tue Feb 17, 2015 6:56 pm

I had a m/cycle once with the timing marks on the flywheel (for strobe setting) about 20 degrees out. You might find retarding the timing might help. Basically over advance - it idles sweet but won't rev, to much retard and it is a pig to get to idle but revs sweetly. May depend on how the timing was set.

Another weird one that is presumably possible, is whether the cam is correct? It is usually possible for the engine to run with one (or two) camshaft(s) a tooth out. No damage but weird engine behaviour. I managed it once on a bike (DOHC) and it all looked OK on the timing marks (new belt) but as soon as I rode it, I knew it was out and corrected it. Surprisingly hard to spot from marks if they are not 'exact' as that particular motor was a few degrees out on the cams relative to the crank.

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Re: Bosch Jetronic LE3 info (gti 8v)

Post by rutter123 » Tue Feb 17, 2015 9:23 pm

Have not tried the vac gauge approach as yet but may be worth a go, not sure wot im looking for there tho.
I assumed the mechanical timing had been set correctly as the car was in Citroen Classics in Staines just before i got it having the stem seals done and hopefully a new head gasket fitted.

Compressions are good no1 175, no2 175, no3 173, no4 176 psi.
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Re: Bosch Jetronic LE3 info (gti 8v)

Post by MULLEY » Tue Feb 17, 2015 9:48 pm

Have you checked the ecu? Perhaps someone has a good known spare you can borrow & try to see if that cures the problem.
2002 C5 2.0 HDI Estate - Remapped - It goes better
2011 Mini Cooper D Clubman - it does over 60mpg
1992 TZD Turbo - SORN - slowly getting there
1991 Gti 16V - Blaze is back on the road since 2008
1990 Gti 8Valve SOLD - looks like it's been scrapped
2002 Mini Cooper S - SOLD - i miss this car
1992 TXD - Scrapped in March 2014

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Re: Bosch Jetronic LE3 info (gti 8v)

Post by rutter123 » Tue Feb 17, 2015 10:49 pm

Changed ecu for a known good unit made no difference at all, seems everything i try makes no difference, today i took off all the new bits and fitted all the old stuff back on still exactly the same behaviour, in 1st gear at about 1500rpm the engine will start bucking/lurching as if its cutting in/out, put your foot down and it goes away, above 3k seems better but the prob is still there but less noticable as the engine is spinning that much faster.
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sdelasal
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Re: Bosch Jetronic LE3 info (gti 8v)

Post by sdelasal » Wed Feb 18, 2015 12:29 am

Diagnosis using a Vac gauge: - see for example https://www.youtube.com/watch?v=SdlNwm8OHco .. Good luck!

Is there one ignition coil used by all cylinders ...or are there two coils paired - like 1&3 and 2&4? Are you sure that the petrol is okay?

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Re: Bosch Jetronic LE3 info (gti 8v)

Post by Tinkley » Wed Feb 18, 2015 7:13 am

Manifold leaks at the head to manifold joint usually will give rough idling or no idling. I've had a couple of rubber bike ones go and the motor will run OK except at idle and just above. You tend to notice it on a single.... :wink:

I'm not sure a vac guage will find a leak if it is downstream of the where it's plugged in. Worth a check though as it (manifold) could be the problem. Maybe temporarily run a bit of insulation tape around the joint? May even be the aluminium has hair lined cracked. I had a Sunbeam that cracked the exhaust manifold, but you could hear that. You might get a 'whistle' of extra induction roar if there's a leak so the old stethoscope trick might work, even at idle.

I'd still be inclined to check the mechanical cam timing. On that bike I did, it was probably the sixth time I'd done the belt on it (every 7.5k) and I still got it wrong on one of the two cams!. It's not hard apart from the aggro of removing the hydraulic and alternator belt, I assume it is like the normal 1.6/1.9 layout.

Worth going through the electronic ignition and making sure the coil(s) are grounded properly. Also possibly the main battery earth to g/box. If it is like a few electronic timing systems the trigger is simply an spinning round part with two apertures, non contact 'sparking' across an air gap to a pair of 'receivers, one pair per cylinder. If the electronics are potted, check for cracks in the potting. I have known such systems fail, almost similar to a dizzy cap cracking with the most minute almost invisible cracks.

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Re: Bosch Jetronic LE3 info (gti 8v)

Post by Vanny » Wed Feb 18, 2015 4:55 pm

An excellent source of information for 80's era BOSCH engine management is the Bosch Automotive Handbook which covers both system and component level and has specific chapters on LE Jetronic and MoTronic systems (in the 5th and 6th editions)

http://www.ebay.co.uk/sch/i.html?_odkw= ... k&_sacat=0

I've not got a copy of the more recent 8th/9th editions so i can not guarantee that it contains Jetronic information, but i've your going to try and work with any Jetronic/Motronic system i would strongly recommend you get a copy!

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Re: Bosch Jetronic LE3 info (gti 8v)

Post by MULLEY » Wed Feb 18, 2015 10:19 pm

Could there be a problem with the electrics that cause either the ecu or the jetronic system to lose some voltage which causes the erratic performance you've described? Is you car fitted with the fuel pump damper device? I doubt this has any bearing on the problem tbh, but could it be leaking or causing a drop in fuel pressure when under load? I can't think of anything else to suggest, vanny's suggestion above seems a definate way of troubleshooting, if the problem is being caused by the jetronic part.
2002 C5 2.0 HDI Estate - Remapped - It goes better
2011 Mini Cooper D Clubman - it does over 60mpg
1992 TZD Turbo - SORN - slowly getting there
1991 Gti 16V - Blaze is back on the road since 2008
1990 Gti 8Valve SOLD - looks like it's been scrapped
2002 Mini Cooper S - SOLD - i miss this car
1992 TXD - Scrapped in March 2014

I'm not just a username, i'm also called Matthew.

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Re: Bosch Jetronic LE3 info (gti 8v)

Post by rutter123 » Thu Feb 19, 2015 10:00 am

You could be onto something there Mulley, i have stripped down the engine loom and repaired/rewired the injectors cos the wiring joints looked dry/corroded, there could poss be a prob further down the line i.e somewhere towards the fuel pump, i have run the engine a varying rpm's with a meter on the fuel pump but the voltage seemed pretty constant at 12v, could poss be a break somewhere which has not yet been discovered.
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Re: Bosch Jetronic LE3 info (gti 8v)

Post by G820_ALB » Sat Jun 06, 2015 12:36 am

Funnily enough mine is very hesitant around the same rev range, engine lurches tried all sorts but can't fix it, goes like an absolute rocket above 3 grand though so probably got different issues. Annoys me greatly but I haven't a clue where to go with it now...

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Re: Bosch Jetronic LE3 info (gti 8v)

Post by rutter123 » Sun Jun 07, 2015 3:31 pm

The lurching no longer seems to be an issue, this disappeared after the MOT, the mixture was very rich running up at 6.9 wound it down by leaning the mixture out with the screw on top the airflow meter now down to 2.7 ish, my guess is the rich mixture was causing the lurching, secondly have you checked the cold start valve or supplementary air device is working as this can cause havoc with low down hesitation if stuck slightly open, I have completely removed mine as this seemed to sort some running probs.
90 BX Tzd turbo 294k SORN undergoing major surgery
90 BX Tzd turbo estate 46k awaiting surgery
65 Peugeot Boxer Van the new workhorse
52 Toyota Rav4 180k Bulletproof Jap reliability