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Topic: Miss Fire.. (Read 437 times) |
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Phil_Waller
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GSO Person
Posts: 443
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Miss Fire..
« on: Nov 29th, 2004, 12:54pm » |
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Hello guys..
I am great at working through other peoples problems but crap at looking at my own issues..
Firstly I know I need to look at the OBD ( I am going to ask Eric if he would be good enough to plug the laptop in)... But before I do that i just wanted to pass this one past you guys.
At idle and up to about 2500 rpm by 2.3 engine has a very slight missfire. At idle and in N you raise the revs and hold them and there is a clear missfire. When i am driving the car I dont feel it.,
I am a very fussy and things like this will nakr me until they are fixed.
My theory is this and this is where i need your expert knowledge.
A missfire is due to ignition problems or fuel/air problems
I have just given the car its 80000 mile service in an attempt to resolve the missfire. The plugs and the leads were replaced. Whilst smoother all round the missfire is still there.
I understand that the 2.3 suffers from the following
Ignition -
The wiring loom along the top of the engine gets hot and becomes brittle.
The ignition modules on top of 1 and 3 can start to fail? I am not sure on this one
Air/Fuel -
The throttle body gets dirty and needs cleaning?
The HEGO sensors can start to break down (more than normal)
We cleaned the MAF the last time we did the OBD but I may do it once more to eliminate dirty eliments.
What else should I look for? The missfire is at the lower end of the rev range which is when most of the driving is done.. Maybe this is why I am getting poor MPG?
If I cant sort it I will book it in and they can check the emissions etc..
Any help is very much appreciated.. 
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1998Scorpio 2.3i 16v Ultima
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Eric_R
Administrator
Cosworth Owner 1998 - 2006 & site co-founder
Posts: 1792
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Re: Miss Fire..
« Reply #1 on: Nov 29th, 2004, 4:03pm » |
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Phil,
Yes, we can scan the OBD again for sure 
The most common misfire problems on the DOHC models have proved to be the wiring to the HT modules - the Fuel Cut-Off loom. Once this is replaced, the next most common is a failure of one of the ignition modules - the poor wiring cooks the electronics.
The next issue, especially for the part-throttle misfire, is a loose EGR pipe, either at the inlet system or the EGR valve end. If this is fully tight, you next need to check out the upstream HO2S sensor.
One owner (of a 24V though) reported a poor idle and a part throttle misfire and when we scanned his OBD we found that the upstream sensors were flatlining. He changed both the front sensors and the catalysts and was horrified when the car ran even worse  - but then we scanned the OBD again and found out that the muppets had changed the downstream sensors instead of the pre-cat ones. Once they were done the car ran beautifully.
Give me a bell when you have an evening free and we'll plug in the lap top.
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After a Cosworth, anything else is just ... ordinary
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Phil_Waller
Full Member
GSO Person
Posts: 443
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Re: Miss Fire..
« Reply #2 on: Nov 30th, 2004, 12:53pm » |
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Thanks Eric - it probably wont be this week. But deffo next week. Will ring.
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1998Scorpio 2.3i 16v Ultima
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