iddle revving too slowly

[Tuga2112]

for those wondering, no this is not related to the "very rought start and fail to iddle after head gasket change" topic.

this issue is happening on the other elan.

i parked it while trying to get the windshield replacement sorted, done a few bits and bobs here and there, but when finally got the windshield supplied the car has this interesting problem.

it does start. but then the iddle dies off. sometimes it wont start at all and just spin and spin with every now and then the sound of almoust getting there
IF i put the foot down, it will start all the time and stay running. but only untill i let it rest to iddle, and then it dies off again.

the car was running absolutely fine when i parked it.
I have replaced the spark leads on it with uprated ones, reason being that i broke one of them when removing them to swap the plugs.
so the car now has a brand new set of very low resistance leads and Denso plugs.
i have topped up with new fuel and done a compression test. from the compression test all cilinders where peaking at figures close to the 10bar
i think that seems about right, anyone can see a problem there ?

Initially i though the issue was air delivery, so i cleaned up the air filter using my air compressor gun, some crap came out but nothing major.
from the compression test i get the impression the problem is not air intake, which leads me to the fuel delivery.

Dave mentioned theres a possibility the one or more injectors could be gummed up from being stopped for a while so i poured in a bottle of redex under the assumption he was right. and spun the engine a fair bit. it seemed to start to improve and try to fire up more often, until the moment it really started up.

so now, the car is in a odd position where given 3-5 attempts it starts up and maintains iddle. BUT the iddle seems extremely low revs (the rev counter in the dash is broken)

last time i started it, i put the foot lightly in the throttle to let it rev a bit higher for a while, when revving there was black smoke coming out, it also was reducing amount over time, when the black smoke stopped appearing, i let it iddle again. and this time the iddle seemed a lot healthier, with some minor white smoke coming out.

switched it off and tried to start engine again... at the 3rd attempt it fired up and stay running... but i was back on the "low rev not very regular" style of iddle.

the air filter does not look in the best condition, but my yellow car was running perfectly fine with filter worse than this one.
i am wondering if this simptoms could be related to a partially blocked fuel filter maybe ? what else would you guys look for ?

I cant think off the top of my head of any safe way to test for fuel delivery.
Althoug one thing i havent tested for yet is the spark plugs themselfs sparking.
I understand i can trip the innercia switch, run the starter for 30 seconds which should clear out the fuel from the engine.
The spark plug needs a ground somehow, im not sure where to ground it. where do you guys ground plugs when testing ? also, is it possible do test this alone ?

[Steve A]

Whilst reading your symptoms I was thinking fuel filter,
the worst thing that could happen by changing it is you have the same fault
but you then know it's not the fuel filter.

[Brit-Car-Nut]

It sounds to me like a bad injector or two that are staying open causing a rich mixture (black smoke) and poor running conditions.

If that is the case and you continue, you will damage the engine because the excess fuel getting into the affected cylinders will wash away any oil lubrication causing higher wear on the cylinders and rings.

Another weird thought is that maybe the fuel tank vent is clogged and the fuel pump is trying to collapse the tank in it's attempt to supply fuel. The mention of the black smoke would refute the thought, but pumping the throttle is fairly useless on a fuel injected engine where fuel flow is compute controlled, not increased by an accelerator pump diaphragm.

The only way to verify clogged or damaged injectors is to remove them and get them tested and cleaned correctly. DIY cleaning via ultrasound will only clean the outlet side of the plunger.

There are several YouTube videos showing manual injector cleaning using a battery and a can of carb cleaner, but you could damage the injector solenoid (inside) by applying wrong voltage for too long. Peak/hold injectors are unique in requiring a higher current to quickly open the injector followed by a lower current to keep it open the computer allotted time. Keeping it ope at the higher current level is also detrimental to the solenoid. Since both cars are down, try swapping the injectors between cars and you might get lucky.

Of course, it could be a lot of other issues like a bad sensor/sender. The computer needs to know the temperatures and pressures going on all the time to determine what fuel flow is needed.

When I bought my first M100, it had been sitting in a salvage yard's barn for many years and getting it to start was a pain. I sent the injectors off to be tested and cleaned and it starts and runs fine.

[Tuga2112]

Thanks for the feedback guys, John's idea of a injector sick open seems to explain the black smoke better than a faulty fuel filter, it would also help explain why when I keep the throttle slightly open the black seems to dissipate (less time open between each Revolution)

Far as I'm aware, when we put the key in ignition the fuel pump starts to prime. In your theory is right, I could prime the pump a few times and then take our the spark plugs 1 by 1. If I find a strong smell of petrol when removing one it would be a indication that cylinder injector is stuck open.
Am I correct in this logic?

I will look into swapping the injectors with the other car, at least it's only going to cost the time of swapping to find out if it's an accurate educated guess.

[Brit-Car-Nut]

If your theory is right, I could prime the pump a few times and then take our the spark plugs 1 by 1. If I find a strong smell of petrol when removing one it would be a indication that cylinder injector is stuck open.
Am I correct in this logic?

Unfortunately, only if the bad injector is at the cylinder with the currently open intake valve. If the valve is closed, the excess fuel is in the manifold, not the head and you won't get any indication by pulling the spark plugs.

[Tuga2112]

Unfortunately, only if the bad injector is at the cylinder with the currently open intake valve. If the valve is closed, the excess fuel is in the manifold, not the head and you won't get any indication by pulling the injectors.

sad face

was hoping for an easy workaround

[Simon_P]

Have you checked
Checking CEL
Base timing
Putting it into service mode ie removing sensor input.
That the IAC valve is plugged in and working - pull off a vac hose and the idle may pick up if it does the IAC valve isn't working properly.
All free and easy.

If you can't keep it running to check, slip a piece of thin card between the throttle lever and the stop.

[Simon_P]

Just a thought - could be CTS on its way out making it too rich.
Foot to the floor is flood start so would clear the rich mixture.

[CalElan]

If it was working, and then I do something, and now it isn't working I always double-check what I've just done.
So, look at the plug leads, make sure they're connected correctly and firmly - pull the spark plugs and check they're gapped correctly. You can also get clues from how they look. Are they damp with fuel or sooty?

Then look at the effects of not running it for a while.. injectors are a favorite here - swapping from the other car is a good idea. How easy is it to do a fuel pressure test on these things? That would give you insight into state of pump and filter. I changed the filter on mine about 2 years back - I suspect it was the first time it had been done and there was quite a bit of crud in it.

Good luck!

[Tuga2112]

If it was working, and then I do something, and now it isn't working I always double-check what I've just done.

nothing that would affect the engine.
i took out all the interior, welded the outriggers, fitted new interior, cleaned up the carpets, took out the doors and fitted new weatherstrips, also removed the bumper. so.. im pretty sure nothing related to the engine running.

Then look at the effects of not running it for a while.. injectors are a favorite here - swapping from the other car is a good idea. How easy is it to do a fuel pressure test on these things? That would give you insight into state of pump and filter. I changed the filter on mine about 2 years back - I suspect it was the first time it had been done and there was quite a bit of crud in it.

I fear i cant avoid this injectors swap job. im scared of finding an issue it may be expencive to solve.

[Tuga2112]

Have you checked
Checking CEL
Base timing
Putting it into service mode ie removing sensor input.
That the IAC valve is plugged in and working - pull off a vac hose and the idle may pick up if it does the IAC valve isn't working properly.
All free and easy.

If you can't keep it running to check, slip a piece of thin card between the throttle lever and the stop.

the car had a cel code when i bough it... strangely enough, its not returned after resetting the battery tho.
i will be looking into the injectors first and then follow up your list

[Tuga2112]

Then look at the effects of not running it for a while.. injectors are a favorite here - swapping from the other car is a good idea. How easy is it to do a fuel pressure test on these things? That would give you insight into state of pump and filter. I changed the filter on mine about 2 years back - I suspect it was the first time it had been done and there was quite a bit of crud in it.

I fear i cant avoid this injectors swap job. im scared of finding an issue it may be expencive to solve.

Turns out the other car had no damage in the engine and all the problem was a pooly fitted tensionser (i didnt tension it manually as per manual )
so. the yellow car is completely assembled and ready to drive. i am now a lot more reluctant to swapping injectors.

however. with my newly found knowledge of timing belt/ valves and pistons workings. i feel confident to test John's open injector theory with minor disassembly effort.

my plan
raise the car.
remove drivers front wheel
remove all spark plugs.
ensure leads are far from the engine.
plug complression test into cilinder 1
rotate engine shaft to TDC if compression test gives me a reading. i know cilinder 1 is in compression cicle, if not, spin another revolution
at this point i know either cilinder 2 or 4 will be ending its intake "cicle?" Check LEC or wiki for the firing/spark order of the cilinders and i will be able to "guess/calculate" which out of those cilinders is in the intake cicle.
rotate engine a few degrees back (to ensure the intake valves are open)
use ignition to prime pump a few times, and "take a sniff"
rotate crankshaft 180 degrees. and now i know either 1 or 3 is in the intake cicle. (again, with firing order i will know exactly which one is it)
prime pump. and take another sniff.
repeat for all cilinders

hope everyone is following my though progress.
any flaws in the theory ?

[alan e]

Or you can do it the easy way by putting a long screwdriver where the spark fits so it sits on the top of the piston and turn the engine via the crank when the screwdriver moves up to its highest point then that cylinder will be at max compression.

[Tuga2112]

Or you can do it the easy way by putting a long screwdriver where the spark fits so it sits on the top of the piston and turn the engine via the crank when the screwdriver moves up to its highest point then that cylinder will be at max compression.

it could be in either max compression. or terminating the exhaust cicle.
thats why the complression tester is helpfull

[alan e]

Or you can do it the easy way by putting a long screwdriver where the spark fits so it sits on the top of the piston and turn the engine via the crank when the screwdriver moves up to its highest point then that cylinder will be at max compression.

it could be in either max compression. or terminating the exhaust cicle.
thats why the complression tester is helpfull

You know the firing order so if you start at cylinder one via the crank/timing mark you then move onto the next one to fire and so on for all 4

[Tuga2112]

You know the firing order so if you start at cylinder one via the crank/timing mark you then move onto the next one to fire and so on for all 4

how do i know the timing mark without removing the top timing belt cover ?