Will not idle: Increased resistance on primary coil

[robwright]

Could well be your idle control valve (or idle stabilization valve as it is also known) mate. It controls idle speed and cold starting. Have you tried adjusting the idle speed on the throttle body?

 

[alwigley]

Yes, have tried adjusting the idle speed on the throttle body screw but it makes no difference. Think the idle control valve is working OK - resistance across the terminals is normal and the problem occurs with engine hot or cold, makes no difference. Gave it a try with some air intake cleaner but made no difference, and am pretty sure the fault is electrical due to the effect of turning on any auxillary electrics, but could be wrong !

 

[robwright]

The engine will always stall more as you increase the load on the alternator especially with big suppers like fan motor and demisters. If it is not idling properly this would cause it to stall completely. Did you bypass the idle control valve when you adjusted the idle speed? This is done by shorting out two pins on the test socket.

 

[alwigley]

Hi - new to the forum - recently acquired a beatifully restored '83 in Guards Red, and was only able to use her for a couple of weeks before she developed a wierd idle problem which has been getting worse.

Will fire up and run for a few seconds before the idle drops really low and she dies - can sometimes hold the throttle open and hold her at 1750rpm + and she runs but a little rough. Sometimes I can then get her to idle, but on restart it happens all over again. If I turn on any additional electrics such as headlights, she dies completely......

Have followed the various checks on the injection system/electrics etc., checked all the grounds and the only thing I can come up with is that the resistance on the primary side of the coil is higher than the specification 0.4 to 0.6 ohms being 0.9ohms. So logic tells me that if the primary resistance is too high, then the coil output must be reduced and therefore it could be weak spark as a result.....

Has anyone experienced a similar issue ? Really want to get her running as I arrive at work with a big smile on my face when I can drive her !

Many thanks for your help - will post a picture when I get a chance to take one......

 

[alwigley]

Did not realise you could bypass it, although disconnecting the ICV altogether makes no difference to the problem...... is the test socket the 8 (ish) way connector in the middle by the firewall ? One thing that has thoroughly confused me is that according to the Bosch guide, I should have battery voltage across the ICV leads (with ignition on) but I have no power at all ? Fuse is fine, and have tried bypassing the DME relay but makes no difference.

 

[robwright]

Ah just realised mate yours is an 83 model so I don't think it has the diagnostic socket the same as mine. Just checked on [link=http://www.clarks-garage.com]www.clarks-garage.com[/link]

 

[zcacogp]

Daft Q but have you tried swapping the coil for a known good one? Oli.

 

[alwigley]

Perfectly sensible question - would love to, but don't know anyone around here who has one I could borrow for 10 minutes, and don't fancy spending £40 quid on the offchance....... Having said that, I am pretty certain it's the original coil, ie. 27 years old, so it may be time for it to be retired !

 

[zcacogp]

Hmmm. 'Tis worth asking on here whether anyone has a spare, as there are people who break them around. And you're in West Sussex - whereabouts in West Sussex? Is there a local Indie who may have a spare, which you could borrow for 5 minutes? Take a few cans of beer to win his favour. Failing that, I am sure there are members on here in the local area. I'm in East London, but that's a bit of a jaunt (although you're welcome to drop by and borrow mine if it helps.) How specialist is the coil? As in, would a coil from a similar-engined car of the same era fit? Oli.

 

[FistsOfHam]

My 944 is also an 83 and the only time it did this was when it was low on fuel and was having trouble building up the pressure so could it be fuel starvation?

 

[alwigley]

Must admit I have not tested for fuel pressure/starvation as do not particularly have the tools to do so - there is definitely half a tank of fuel in there, and from the exhaust smell there is a lot of unburnt fuel coming through, so have stayed with electrical/fuel injection faults...... Fuel pump is whirring away nicely as I tested this by bypassing the notoriously dodgy fuel pump relay. Have heard that the fuel pressure regulator on the end of the fuel rail can cause this sort of trouble, which can be proven by the simple expedient of disconnecting one of the injectors, so will have a shot at that this weekend. The coil appears to be pretty specific to this particular Bosch Jetronic system, as it has very low standard resistance on the primary side of the coil, but if anyone out there is close to Crawley and has an early 944 I would love to borrow your coil for a few minutes !

 

[JamesO]

With regards to the coil, had a look at a mates Honda Prelude recently which would not run at all, with no spark. The coil primary was only a very small amount out of spec like yours, (depending on how accurate my meter is) so we checked everything, in the end returning to the coil and replacing it and sure enough it sorted it.

 

[peanut]

ORIGINAL: alwigley Have heard that the fuel pressure regulator on the end of the fuel rail can cause this sort of trouble, which can be proven by the simple expedient of disconnecting one of the injectors, so will have a shot at that this weekend.

you've got that the wrong way round. if the fuel pressure regulator FPR fails to relieve pressure your fuel system will over-pressurize . It is the overpressure that shuts down the ECU and shuts down the fuel pump and injector pulsing. If you disconnect one injector and the car then starts it indicates too much fuel pressure. You can buy a simple cheap fuel pressure gauge off ebay for £10.00 just connect it to the fuel rail with a bit of garden hose and some jubilee clips.

 

[alwigley]

Thanks chaps - very interesting to hear of a similar problem on the Prelude...... What is odd is that I am clearly getting a spark as I can get it to run with a heavy right foot, but lower down the range it just won't hold. Must admit that I thought the idea of disconnecting one injector odd, but apparantly it alters the level of signal sent back to the DME, and taking one off reduces the voltage return, kidding the DME into thinking the pressure is lower ? (Or something like that anyway - I know you can't trust everything you read on the net !)

 

[944Turbo]

I had a coil that was a little out of spec, it actually wasn't consistently out and would change with vibration. It was a 5 or 6 years ago and I cant remember the exact symptoms or values - I think it cut out under engine load and difficult starting. A replacement wasn't expensive, I dropped the old one when it was out of the car and it the resistance then read fine - wouldn't recommend it as a way of fixing it though! Tony

 

[peanut]

ORIGINAL: alwigley Thanks chaps - very interesting to hear of a similar problem on the Prelude...... What is odd is that I am clearly getting a spark as I can get it to run with a heavy right foot, but lower down the range it just won't hold. Must admit that I thought the idea of disconnecting one injector odd, but apparantly it alters the level of signal sent back to the DME, and taking one off reduces the voltage return, kidding the DME into thinking the pressure is lower ? (Or something like that anyway - I know you can't trust everything you read on the net !)

yes thats how it does work but it is only useful in an over-pressure situation. I thought you said you had an under-pressure situation. ie low fuel supply so the last thing you want to do is reduce the fuel supply. I haven't really followed this thread i'm afraid. I suspect there are several possible causes here and you need to do a thorough systematic check of everything using the Clarkes troubleshooting guides.

 

[sawood12]

If you were overfuelling then you'd have sooty deposits on the spark plugs, so you could check that. What about the throttle postition microswitch? These are fairly common failings on these cars as they get older - with a dicky switch your ECU wont know when to hand over control to the ISV.

 

[robwright]

Off thread but good to know you are still around Scott.

 

[sawood12]

Oh yes Rob. You can't get rid of me that easily. Also old habits die hard! I like to keep an eye in for that time when the right time comes for me to dip my toe in the water again!!

 

[barks944]

I have had very similar problems with my lux. Recently I was convinced I had put diesel in it until I finally discovered it was the rotor arm. If I were you I would change the cap/leads/rotor even if it turns out to be the coil. Edit: To clarify mine wouldn't idle and eventually wouldnt start at all. Initially even though it wouldnt idle it would go if I kept the revs up but too much throttle and it would drown the spark and backfire etc.