Race Engine Forum UK

Hi everyone. I'm new to this forum and this is my first post. I'm optimistic that I will be able to solve this problem with your expertise.

I took my 1989 Lancia delta 8V integrale out on a 350 km drive and I had an annoying problem with misfiring above 3500 rpm after about 10 minutes or so of driving the car. I stopped to check if any sensors or ignition wires were loose but everything was tight and well connected. Base idle speed started to become a bit erratic and was moving up and down by about 200 rpm. I stopped and cooled the car for a few minutes and when i drove it again the problem disappeared for about 5 minutes. I could rev it to 6500 rpm without any misfiring but then the problem returned again after a few more minutes of driving.

If i were to accelerate gently the car would pull smoothly until i reach 3500 rpm then it would start misfiring and jerking. If i were to depress the accelerator pedal immediately the misfiring and jerking would immediately happen.

My integrale's engine is basically stock except for the addition of a K&N air filter element and an upgraded exhaust system. I recently replaced the air temperature sensor, engine coolant sensor, distributor cap and rotor, ignition wires and spark plugs (NGK BP7ES gapped at 0.8).

This car is very sparingly used and it's cared for very well.

My question is what could be causing the misfiring problem?

There is no evidence of moisture in the distributor cap. The spark plug wells are dry.

Could this be an electrical problem or is it mechanical in nature?

Thanks in advance for the guidance and advice.

Hi,

this is a long shot because doing diagnostics remotly is usually a big no no. But check this:

-If the car Is revving up and down by itself on tick over you should check if the potentiometer is out of adjustment, the water temperature sensor is faulty, the supplementary air valve is sticking and the air-bleed screw has been wrongly set to compensate.

-If your car is jerky and not running smoothly on the over-run, what is the cause it is probably the throttle potentiometer miss set.

- and my best bet for when the car starts OK and runs OK, but as it warms up it starts to misfires and sometimes gives black smoke from the exhaust it is almost allways the water temperature sensor gone bad.

When did you last change the fuel filter?

G

I've heard of this before with the integrale, it sounds like the crank sensor from memory, and the intermittant issue may be the fact that the heating and cooling is expanding a dry joint within the sensor and causing it to lose contact when warm. I had similar problems with a different sensor on my old Jeep, it would only work when cold, tested it in the oven with a multimeter and sure enough. Or maybe the gap changes with temp? Worth a try anyway

If i were to depress the accelerator pedal immediately the misfiring and jerking would immediately happen.

This part of your symptoms, points to a lack of fuel pressure. The fuel pump (in the petrol tank) has two very short hoses from it, which take the fuel to and from the outside of the tank. These two hoses are well known to break up with age and leak any pumped fuel back into the tank instead of where it should be going. Remove the rear seat for access to it, if they are knackerd in there, you can replace them easily with new fuel hose. Make sure you buy fuel injection grade hose or they wont last long.

Hi Mr. Samo. Regarding the water temperature sensor, it has been recently replaced. Although I may have purchased a defective sensor to begin with. I will also check on the supplementary air valve as you suggested and will also check on the setting of the throttle position sensor and make the necessary adjustments if needed. Any suggestions on the settings that I should make?

Hi Mr. Croft. Yes I have replaced the fuel filter just a few months ago. I have less than a thousand kilometers on it.

Hi Mr. Fingers. That sounds like a possible solution to the problem. How may I ask do I go about checking on the crank angle sensor? What are it’s values cold as opposed to it being hot?

Hi Mr. Tricky. I will definitely check on that. But if I do have a lack of fuel pressure to begin with, isn’t the misfiring problem supposed to be evident regardless of engine temperature?

Gentlemen, thank you so much. I truly appreciate the responses I’ve so far received and yes Mr. Samo I totally agree with you on that it is quite difficult to diagnose a problem remotely. Sadly, living in the Philippines makes it difficult to repair an integrale.

I will post my findings and will hopefully be able to repair it and will post the solution as soon as it’s done.

I would definitely get the injectors checked.

G

Hi Mr. Croft. Is there a method for checking the injectors without removing them from the engine? Do you feel that there is a problem with the spray pattern that only manifests itself when the engine reaches it's operating temperature?

I'd say crank sensor too, pretty violent cut out is it at 3500 rpm? Other than a FL tester I don't know a way to test it's working (electrical idiot!). Quick enough to change over, a bit fiddly to set the clearance.

Hi gentlemen. Through your invaluable advice I have so far solved the idle speed problem. What I did was to pull out the solenoid air valve and proceeded to clean it. It was slightly clogged. After reinstalling it I started the car without installing the electrical connector for the air valve. Idle was then adjusted to 750 rpm then upon plugging in the connector the idle speed increased to 1500 rpm then settled to 850 rpm after a couple of seconds. It remained steady from then on.

Again following your advices I focused my attention to the crank angle sensor. As per factory workshop manual, which I borrowed from a buddy of mine, it states that the value between the 2 terminals should be between 618 ohms to 748 ohms @ 20 degrees centigrade. The reading I got from my ohm meter was 729 ohms. I will take the car out for a drive tomorrow and will recheck the ohm reading to find out if there are any changes when it gets up to operating temperature.

If you find you did not fix the problem after all, I would advice you to do an exhaust gas test. Your symptoms can be caused by a wide range of causes and it usually helps to see if it's fuel related, or spark. By doing an exhaust gas test you can eliminate things in the fuel/mixture part of things, unless the ignition is so bad that your engine is skipping.

WhizzMan wrote:If you find you did not fix the problem after all, I would advice you to do an exhaust gas test. Your symptoms can be caused by a wide range of causes and it usually helps to see if it's fuel related, or spark. By doing an exhaust gas test you can eliminate things in the fuel/mixture part of things, unless the ignition is so bad that your engine is skipping.

Thanks for the advice Mr. WhizzMan. I'll do an exhaust gas test too. It's just strange that the misfiring only happens after 10 minutes of driving the car.

Hello
This case is -surprisingly- very similar to mine. My car is a supercharged Alfa 166 2.0TS facelift.
I observe the same symptoms as yours,the only difference being that the misfires occur at 4.000 rpm and above.
Through Fiat EcuScan (diagnostics through OBDII) I got the error message for misfiring on cylinder 4. I changed spark plugs from cylinder 4 to 3 to see if they are causing the misfire. The problem remained on cylinder 4. Before doing swap of spark plug wire+coil of 4 to 3, I performed a check on the fuel rail and injectors the day I got the misfire again (yesterday).
This time misfire was observed to cylinder 4 AND cylinder 1 (Fiat EcuScan).
To my very big surprise, I found a small plastic debris coming from the plastic clamp of the fuel line connecting to the fuel rail. This small plastic broken part was inside the inlet of injector cylinder 1.
What I have done today is that I cleaned the injector rail very carefully, I changed the injector of cylinder 4 (I have spare one) and I mildly cleaned all injectors with a cleaning solution (no mechanical cleaning).

If the problem remains, I will swap spark plug wires+coil of cylinder 4 to 3. Keep in mind that electrical/electronic failures that have to do with inductance/resistance tend to occur at high temperatures, so that could explain why you (and me) observe the problem only when the car is at operating temperatures (eg after 10mins).

I would also recommend scanning the ECU for error codes. Otherwise it can really become a nightmare searching for a intermittent misfire cause. An example screenshot of error codes available within IAW ECU of similar generation like used in Integrale 8v: Apart from that, it is worth noting what the rev counter is showing when it comes to misfire. If the needle is erratically jumping, or going back to 0, the problem is clearly electrical, most probably either ignition system, ECU, crankshaft trigger or camshaft trigger or wiring.

Hi Mr. Kpsig. Your problem sounds very similar to mine and as what Mr. Croft pointed out on his earlier post it too may be an injector problem. I'm definitely going to pull out the injectors and have them cleaned.
Many thanks for your advice.

Hi Mr. NickRP. In as much as I'd like to have my car diagnosed through a scanner unfortunately in my country we don't have a scanner for a Lancia or a Fiat. As per your statement pointing out that if the rev counter bounces around erratically or drops down to zero, fortunately my car doesn't do so. The rev counter remains steady it's just that the car refuses to rev past 3500 rpm while on full throttle.
Many thanks for your insight and advice.