C531XHO

Hi all, sometime since my last post but I have been busy "fixing" things... or rather doing work without gain so far....the car had been sitting for a long time before I bought it. To date I have completed:-
- TB & balance belts
- Fuel strainer check (clear) and fuel change
- DME relay repaired and jumper made up for testing
- Replacement ECU fitted as previous one water damaged
- Oil pressure recovered by applying compressed air to dipstick
- New battery fitted
- Fuel pump jumped direct and found to flow when jumped on DME
- Speed and reference sensors checked for resistance - ok, not checked for pulse yet but I have seen tacho bounce
- Made up a noid light and checked all injectors clicking, although not checked with leads attached, just linked to battery
- Checked spark getting to plugs
Still can't get any sign of starting despite work, plus tacho bounce seems to have disappeared but can't find any loose connections. Frustratingly the speed and ref sensors are stuck fast despite twisting, wd40 spray and hot water. I guess the next step is to put an oscilloscope on them to see if they are pulsing and worry about removal/clean/height setting only if there is something wrong with the signal. In the meantime I have ordered fuel pressure test gauge and proper Noid light to confirm fuel supply side but is there something else I am missing?

David
85NA

931guru

No tach bounce means no ignition.

If you think you have ignition, spray some ether in the intake and see if it starts (momentarily). If so, then fuel supply is bad (either no fuel or no injection pulse.)

marc abrams

Compression??

C531XHO

Ok but why bounce then no bounce, I am assuming electrical connection in the DME loom?

pyropete125

I just had a similar issue. I had a small racing type AGM battery and it just didn't have enough juice to keep everything wit the supplied voltage when cranking especially with hot restarts. I put a regular sized new battery and it started fine and no more intermittent no starts.

Humboldtgrin

Has the fuel turned to turpentine from sitting too long? You may just need freash fuel. May also be the DME temp sensor messing things up.

C531XHO

Changed the fuel and cleaned the gauze filter but didn't drain the lines. This should have diluted after recirculating by now.

Re DME temp sensor, what effect would this have?

David

C531XHO

I think mine should be ok, it's regular size and brand new. I think 65amp hrs or so...

C531XHO

Still stuck and really confused. Tonight I noid tested the injector plugs, all firing. Tested the spark at every plug lead, all firing. Checked fuel pump operation and measured rail pressure at 2.5bar. Still no sign of starting, what next?

David
85NA

marc abrams

If you want to rule out the fuel system, pour some fresh gas down the throttle body. I don't like using ether on gasoline engine's. Did you check the compression ???

marc abrams

Not trying to insult you but double check the firing order also.

odonnell

Could be too lean to fire - bad DME temp sensor can tell the DME to add too little cranking enrichment.

C531XHO

[QUOTE=931guru;12622986]No tach bounce means no ignition.



Hi I put a scope on the speed and ref sensors output. Speed looks like a nice sine wave and about in spec voltage wise but should it be saw tooth with more defined edge?


Reference output looks ok? Periodic peak per tdc??

odonnell

No, they are an analog signal until the DME processes them into a digital signal.

C531XHO

Ok great. Suspicion then turns to wiring between sensors and DME methinks as I had tach bounce but only briefly...