engine hesitation

[Alan L]

I have read all the suggestions on this thread, and followed most.
But my SC has had this problem as long as I've had the car - about 5 yrs.
It hesitates under light throttle load at around 18-- 2200 rpm. It is fine cold, but bad when hot. Richening helps - it cuts down the rpm band width and shifts it higher up. The only way to get past this hesitation is to give it plenty of throttle.
I've been thru all the CIS fuel pressures, air leaks, ignition wires etc. Eventually fitted new injectors figuring nothing left to look for.
Made no difference. Still hesitates.
Any other suggestions.
I have the engine out at moment for overhaul.
Thanks
Alan

[ThePointman]

Bump ...

[wesayso]

I would still suspect the ignition if it only happens when the engine is warm. Did you disconnect the O2 sensor? that's one factor that changes if the engine heats up (if you have one, what year or type is it?)

Did you place new wires or check the resistance. The resistance on my wires was good but the wires were bad (when warm) and shorted. I wouldn't replace any parts untill you know what the problem is. Some simple tests should point out wich part is failing. Those tests are easyer with the engine in the car.
What were your plans? Why is the engine out of the car?


Here's my adventure...

[Alan L]

Hi there,
Thanks for advice. I checked the resistance on the HT leads, and all were good - but you have a point - they may fail when hot.
I'm not sure I have an O2 sensor - never seen anything that looks like one. What I have suspected is an imbalance between the air sensor and fuel pressure/temp unit. But nothing I do in this department seems to help either.
Will check the leads again. Mine is an 83 SC, but I also have an 82.
I could try swapping the HT unit over.
The 83 has a couple of broken head studs, so I decided to give it some TLC. Stripping it to the crank. Crankcase about to be split.
Regards
Alan

[jluetjen]

My experience is that ignition mis-fires tend to be fairly violent. When they happen it's like the car starts bucking. It sounds to me like your mixture is lean. Why -- could be due to settings or air leaks. The only way to know for sure would be to check the exhaust O2 content or temperatures while the engine is under load.

Unfortunately, I'm not that familiar with the CIS tuning, so I can't really propose any fixes.

[stlrj]

Even with new igntion cables I would still suspect an igntion problem.

Try spraying some windex on your ignition cables while the engine is at idle and see if you can get it to miss.

Joe

[Alan L]

Thanks Joe, John.
I have oscillated between fuel and electrical by the feel of the miss. But it is a definite misfire, rather than a flat spot. If you leave it in this position, it gets worse til the car almost does not want to go. But it can be overcome by giving it more throttle. I have had the fuel mixture tuned, and still there. Have richened it condiderably (3% CO) compare to 1.5-2.0 spec. Still there - altho less.
I suspect I'm back to the HT area.
Not familiar with Windex - don't think we have that in the antipodes - do you have another description?
Regards
Alan

[stlrj]

Windex=a clear liquid glass cleaner that leaves no residue

Since changing the mixture has little or no effect, it is definitly not mixture or fuel related. So I would concentrate on ignition.

Joe

[dhoward]

No windex, use water. Same effect on leaky ign wires.
ALTHOUGH, this would turn up anytime it rained, and not at a specific RPM....

[dhoward]

Originally posted by Alan L
Snipped......
I have had the fuel mixture tuned, and still there. Have richened it condiderably (3% CO) compare to 1.5-2.0 spec. Still there - altho less.....Snipped

So....changing the mixture DID affect performance.
could be mixture on ONE cyl at that RPM range....

[wesayso]

My bet is still on the ignition. Keep us posted on the outcome...

[dhoward]

You're on....

[Alan L]

I replaced all the injectors with new ones.
Made no difference.
The leaner the mixture, the earlier the misfire develops as the engine warms up. ie, if it is tuned rich, it make take 15 minutes of higway driving before it starts coughing in this rev range (and only this rev range). If it is tuned lean, after 5 minutes it will start.
Because it seems to be affected by fuel mix/throttle, I have chased the fuel side. But I have never been able to cure it this way.
So, thinking back to the HT side, by elimination of possibilities. Those HT wires are getting old, even tho their resistance checks out perfectly.
Alan

[dhoward]

Resistance is a poor measure of HT wire condition. If anything, it will only prove the wire isn't broken. Have some fun, build a new set out of some Accels or other aftermkt universal wires and test your theory. What, $30 and a 1/2 hour or so?
Trust me, they work.
....and for more fun, spay a little carb cleaner around the base of the intakes and TB shafts to see if you get a reaction....
Have fun!

[Alan L]

Yes, I suspect the resistance test is inadequate as a means of telling me the leads are up to spec under real conditions. It may have simply thrown me off the track for a long time.
I have been down the carb cleaner track and eliminated all air leaks. Sealed the injector area with silicone, replaced all injector seals.
I think I will make up a new set of leads - as you suggest. Run out of most other options.
Thanks for advice.
Regards
Alan

[stlrj]

the resistance test is inadequate as a means of telling me the leads are up to spec under real conditions

That's why I suggested spraying a fine mist of some commonly available liquid on the wires to provoke a missfire at the problem area.

Cheers,

Joe

[Alan L]

Hi Joe,
The engine certainly ran no differently in wet conditions.
If it was up and running now, I would try this.
But I have it stripped down to crankcase at moment. Will make up some new leads. Everything very accesible right now. Have checked the intake rubbers, all connections etc for leaks. Nothing.
Will let you know when I track it - if I do. Will be a month or two until I get this rebuild finished.
But I have lived with this problem for about 5 yrs. Annoyed the hell out of me. The only complaint I have had over this car. Other than that, it goes brilliantly.
Regards
Alan

[stlrj]

Alan,

I hope it all turns out well for you.

Cheers,

Joe

[E30Mracer]

I have simmilar problem with my 75 911S. It buckles and shakes in first and second gear when at around 2000k At some point i thought that adding injector cleaner helps. But not really. I too suspect ignition problems.i also liked the $30 Accel wire test set. So how do i build it?

[Alan L]

There is a procedure to quick check your injectors - which from memory means removing them and turning ignition on so fuel pump is up to pressure. Then watch the pattern and collect the fuel in a measure over 30 sec.
You have to lift the air plate from memory.
Someone else may be able to give more accurate description - I think you have to jump the terminal on your fuel pump at the fuse box from memory. If you have a dud injector, you may pick it up. Check the injectors at low fuel setting - which is where your problem is.
Alan