Thread: Slight Miss 3.5 V8 Disco

Just wondering

After you cleaned the MAF, was the slight miss gone with the engine at normal running temp?
I did read your earlier post that it re-occurred after 15 min or so, but was that from stone cold or was it warmed up before you went for a test run?

Originally Posted by malrv1

That,s interesting. What sort of impedence reading should I be getting?

3 to 5 K ohms per lead is far better than the 1 to 2 K ohms of some "performance" leads. The problem is one of damping. Just like your suspension will resonate at a particular frequency and needs a correct shocky, the rate of an ignition pulse is damped by the lead's resistance and inductance. Too low a resistance gives back EMF which may mask the ignition pulse under certain conditions. As I said my problem was like yours, only apparent on a hot engine at a particular revs. It made smooth take-offs impossible, I had to floor it every time in hot weather.

It was from stone cold. It always runs OK until it gets to normal operating temp. Usually after I have stopped and then restarted. Like if I go down town and make a few stops hre and there, it is OK for the first part of the run while warming up and then plays up after the first restart.

I understand what you are getting at, but I have had Top Gun leads on the car for years, it is 19 years old and I have only had to replace the leads once before this and I used Top Guns then without a problem.
THX

I had my Top Gun leads on for 4 years so they were fine most of the time. I suspect they do get their cable in bulk from different manufacturers and so their design may change. I used to personally go to the local Top Gun agent and watch him make up my lead order. I sold quite a few sets in my business.

Every so often I find Bosch leads with low resistance, usually when I am diagnosing running problems. So it is just something else to check.

Originally Posted by malrv1

It was from stone cold. It always runs OK until it gets to normal operating temp. Usually after I have stopped and then restarted. Like if I go down town and make a few stops hre and there, it is OK for the first part of the run while warming up and then plays up after the first restart.

This is from an article ive refered to before, you can test the values of your sensor with the info below,

Engine Coolant Temperature Sensor

The Engine Coolant Temperature Sensor is threaded into a boss on the intake manifold. Note: this sensor contacts the coolant fluid, and thus its threads need to be sealed appropriately. When the engine is "cold", as determined by this sensor, the ECU richens the fuel mixture by lengthening the time injectors stay open. The ECU reduces the length of fuel pulses as the engine reaches normal operating temperature.

The Coolant Temperature Sensor should change resistance with heat, per the following specs. 10C (14°F) 9100-9300 Ohms 0C (32°F) 5700-5900 Ohms 20C (68°F) 2400-2600 Ohms 40C (104°F) 1100-1300 Ohms 60C (140°F) 500-700 Ohms 80C (176°F) 300-400 Ohms 100C (212°F) 150-200 Ohms

Thanks for that. I am off to Sutton Motors this morning to get them to plug in their ECU reader just to see if that brings anything up.