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Discussion Starter · #1 ·
My '87 Spider Veloce will not start when engine is cranking. We have 40 lbs fuel on the rail, good spark in all spark plugs, cold start injector works fine, air balance working, 120 psi in cylinders 2, 3, 4 However, 90 psi in cylinder 1.

When cranking, there is a back-pressure "pop" of air and fuel coming backwards through the intake manifold.

Any thoughts as to what is causing the engine from starting?
 

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Sounds like timing. Have you checked the timing of the distributor, plug wires, and wire to the coil? The engine will still self start and run with 90 PSI in one cylinder. You have to get down to around 45 PSI in all cylinders for the engine to cease self starting with the starter motor turning over the engine. Did this start all at once or come about gradually?
Robert
1988 Black Spider Veloce
 

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What work have you bin doin?

Additional ro Robert's good stuff..are the Fuel Injectors getting signal?

The CSI should at least get you a short burst.

I trust you have at least 10.5V for the ECU's while cranking.

TTFN Elio
 

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The pop could be due to an intake valve leaking, misadjusted, cracked, or burnt resulting in a spark igniting the intake air/fuel charge.
Possibly at the low cylinder.
 

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Discussion Starter · #5 · (Edited)
Thank for all the advice - some clarifications.

1) Previous owner said the car stopped running while driving - had sat for a year before we bought it.
2) The iginition wire timing is proper - checked TDC and plug 1 setting as well as wiring sequence.
3) We pulled injector on cylinder #4 and confirmed a nice atomized spray - we are new to fuel injection so not sure what a "good spray" should look like.
4) Have not confirmed voltages except in major electrical areas (fuel pump, coil etc) - concerned about frying ECU - any help here welcome.
5) How can we check proper operation of the Throttle sensor, flywheel sensors and Air Balance? Can these prevent starting?
6) Could an advance timing solenoid problem cause the "pop"?

We will confirm which cylinder is firing when the "pop" is heard.

Thanks again to everyone... I am tending to suspect the valve problem, but am surprised none of the other cylinders are firing.
 

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Testing of flywheel sensors and other items are outlined in the L-jet diagnosis page. Link is in my signature.

From what you are describing (spark & fuel present) I'd suggest looking carefully for any intake air leaks. L-jet is very intolerant of intake air or vacumm leaks. Check the four rubber plenum to intake hoses. They are hard to see as they are down under the plenum. Cracks and splits will cause grief.
 

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Discussion Starter · #7 ·
Many thanks - the info in the link was perfect.

I seem to have a "sensor" located between the #3 and #2 injector. It has an off-white connector and I cannot identify it in any documentation. Any ideas?

I do think the temperature sensor is bad - it registers infinite resistance at cold.

Will test the timing sensors later today.

Thanks again.
 

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I seem to have a "sensor" located between the #3 and #2 injector. It has an off-white connector and I cannot identify it in any documentation. Any ideas?
That would be the coolant temperature sensor for the ignition ECU.
 

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Discussion Starter · #9 ·
OK - so now I am confused?? Are there 3 temperature sensors? I have identified the Thermo-tine and Temperature Sensor (between #4 and #3 injector) and there is also this 3rd Coolant Temperature Sensor? How do all of these work together?
 
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