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Discussion Starter · #1 ·
Hi, im guessing this is a simple question for most of you, i am new to the opel efi setup so will start with basic question, my 2lt motor used to start fairly well when warm, just turn the key and it started, i then renewed valves and also some efi lines near manifold. Now it takes a bit to start and maybe a minute running to idle reasonably but when engine is hot it tends to idle up and down between 1000 - 1500rpm like a diesel hunting. Ive checked manifold bolts - all good. The last car i had with electric fuel pump i could hear it working when i turned on ignition, this is silent?? wondering if there may be a problem with it or maybe time to swap out fuel filter under car?? Guess im just hoping for advice for easy fix. Any input appreciated.
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If you can access the wiring for the fuel pump check amp draw. If no amperage shows, with power off to the pump safely disconnect both wires & check the wiring to the pump using an ohmmeter, if it’s an open circuit and you can verify nothing is between the wires and the pump motor you will likely have to replace the pump. If you have amp draw that match the specs, replace the fuel filter. You can also tee in a pressure gauge to measure its output.
 

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Discussion Starter · #3 ·
Thanks i will do tomorrow. Also with the 75 EFI set up ive got i cannot see a cold start injector.. is it an easy thing to have been deleted/taken off for some reason, cant even see where it would have been unless on top/motor side of manifold where there is now a spiggot and hose attached. May at least account for lousy cold starting.
 

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Discussion Starter · #4 ·
Ive just read a past thread stating that there is no room at rear of manifold for cold start injector when fitted to GT so guess that answers that question. Might be able to plumb one in at different location but sounds a bit hexy.
 

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On the old Jetronic system, yes there is a cold start injector. And yes it is at the back end of the intake manifold. But that would not explain the idle hunting up and down when hot.

This idle hunting is most likely due to the idle throttle setting being wrong, or the cold idle air bypass hanging open.

My stock Jetronic fuel pump is very quiet. To test that and the regulator, you have to use a tee to put a fuel pressure gauge anywhere in the line to the injectors. You ought to see somewhere in the mid-30's psi range at idle, and it ought to peak up higher when you blip the throttle. The fuel pressure regulator varies the pressure inversely with intake manifold vacuum; the fuel pressure will increase 1 psi for each 2 inch decrease in intake manifold vacuum.
 

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Discussion Starter · #7 ·
Thanks for all info, ill give up on having a cold start injector then, will look at cold idle air bypass, i played with various settings yesterday including timing, now seems to idle better but at 1300rpm. I dont know history of motor but has a fair old cam in it, no advance/retard vacuum setup on dissy, solid lifters and hi comp pistons. Is fairly ordinary up to 3000rpm or 100 kph and then runs like a charm 110 - 130kph, very quiet and smooth with plenty of power left in it.
 

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Many times you will see the cold start injector relocated to a flat spot on the rear engine side of the plenum. You'll know the spot, as it almost looks like it was made for that purpose. Also, on my 75 FI cars, the fuel pump doesn't start working until you turn the key to start, IIRC.
Allen & Vickie Gage
 

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Thanks for all info, ill give up on having a cold start injector then, will look at cold idle air bypass, i played with various settings yesterday including timing, now seems to idle better but at 1300rpm. I dont know history of motor but has a fair old cam in it, no advance/retard vacuum setup on dissy, solid lifters and hi comp pistons. Is fairly ordinary up to 3000rpm or 100 kph and then runs like a charm 110 - 130kph, very quiet and smooth with plenty of power left in it.
Where did you end up for base ignition timing? Some advance over the stock specs for the '75 is deiriable but if you do have high compression pistons, then you need to take careful measurements of advance versus RPM's, and not exceed something like 35 degrees + or - at high RPM's. This ignition advance needs to be referenced to actual #1 cylinder TDC, not necessarily the ball on the flywheel.

The throttle idle setting is the setting of the set screw that determines how closed is the throttle plate. (I was not referring to the idle mixture setting on the air flow meter assembly.) That set screw needs to be set so that the throttle is almost fully closed. THEN you make other adjustments with the engine all warmed up.

IIRC, the cold air bypass device has no adjustments. (It is the odd-shaped device on top of the thermostat housing, with the approximataley 1" OD hoses going in and out, and a 2 wire electrical connector.) These devices are electrical and gradually close a small shutter inside as they warm up, shutting off the extra cold idle air flow, and it is common for them to not work well or at all. If it is not closing the internal shutter, then you idle air flow will always be high and you will never get the idle speed down. To see if it is closing when warmed up, pull the output hose (the side that connects to the manifold hose 'tree') off that device and plug it, and see what is your warmed-up idle speed. If it drops a lot, then the cold air bypass is not closing when warmed up. Mine was 'dead on arrival' and I just manually rev the egine while warming up,as these are not in produciton anymore, and the replacement (like a Nissan unit) cost something like $150-220 USD!

I'd advise you to get the '75 technical manual supplement. (With the purple cover). It has thorough test procedures for all these parts.
 
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