Engine Suddenly Running Rough

[xceptional]

It's been a while since I was on this forum. Last time I had an issue whereby the BA XT6T would loose power under boost (running factory standard). Eventually found that it was the catalytic converter. All the honeycomb had been burnt out, rattling around and restricting the flow.

Anyway since it had to be replaced I decided to go with a hi-flow cat and exhaust, injectors, monster process west intercooler, upgraded turbo attenuator and larger dump pipe, a flash and custom tune to bring the kw to 265rwkw running only 6-8 lb boost. Later a new set of valve springs and a re-tune at higher boost should see me bust over the 300rwkw. Well, that will happen soon but I have an issue that started just a day ago.

It's similar to the earlier problem with no power but this time it's all over the place. I have an idea what it is but want to know if any one has had a similar experience and what they did to fix it.

The other day I was driving home from work and only a couple of min into the journey (motor still relatively cold) it started missing. The engine light would flash and while I had the radio on I could here electrical interference. It sounded like small ticking or cracking or an electrical arc in the radio. Turn the radio off and the sound stopped but the motor still missed. It is most noticeable in the lower rpm, when idle or just starting out from idle (when there is some load on the motor). It's pretty smooth from about 1200 to 2800 or 3000 rpm with only an intermittent miss or crackle in the radio. After 3000 rpm the missing becomes very noticeable and the engine accelerates very roughly. The boost seems to be still there but not as strong. The motor vibrates pretty bad until I button off. Obviously I don't drive it like that any more.

It's worse in the morning when cold. Motor runs very rough and lots of static through the radio. After 15 min of driving and motor is at temp the missing is only very intermittent and mostly when idle at lights then moving off, or when hitting the real boost around 3000 rpm.

I took the car to the place where I had all the work done and they put a computer on it but did not come up with anything.

Does anyone have any ideas? I have a couple but don't want to say until I have had some feed back so as not to skew diagnosis.

Thanks in advance.

Cheers

[senna_T]

Normally I would suggest coils and plugs, however the engine light doesn't normally come on when the coils are faulty. Have you checked all the earthing straps on the motor? Could be a bad ground causing the electrical interference

[xceptional]

Good point about the grounding. Haven't thought of that. Now, how many earthing straps are where are they located?

My initial thought was the coils and or plugs as the electrical interference in the radio would suggest electrical. However I changed both at the same time in Nov 2008 (about 20,000ks ago) trying to fix the first problem I was having mentioned above, which did not fix the issue therefore the coils I took out are all still good. I have heard of the coils shorting on the covers too. To help prevent this I wrapped each coil head with electrical tape to provide further resistance against shorting. The plugs I took out are pretty munted so will discard those.

I replaced the inline filter and the in tank filter around the same time I did the coils and plugs.

The other possible cause could be a bad batch of fuel but weir why sometimes it's good and sometimes (especially when cold or under load) it isn't.

Anyway if you tell me where to find those earthing straps etc it would be helpful.

Thanks senn_T

Cheers

[John_K]

Sounds like grounds to me too, but Pat beat me to it.

Crackling in audio sytems are a major indication of poor grounding.

Check your earthing points and upgrade your grounds with some 2 or 0 gauge cable.

[senna_T]

From memory there is an earthing strap on the drivers side down near the crossmember. There are other ground located around the car, but I would assume one near the motor would be more likely to some loose due to the vibration in that area...

[ebxmple]

Yeah,check the earths and the battery terminals first and if they are ok check your coils. The engine light does come on if the coil is stuffed proper and is arching through the side. Pull all your coils out and inspect them for signs of arching around the coil casings. If its a type A missfire it will stuff your cat.

[xceptional]

ebxmple. What do you mean type A missifire and does it take to munt the cat over a period of time. The missing only occurred late Thur arvo. Hope it hasn't damaged anything during this time, but how would you know.

Cheers

[ebxmple]

HAHA its just a term they use at ford. Type A and type B missfires one of which is worse as it effects emissions and inturn turns the light on and can destroy cats. It shouldnt of affected your cat yet so best get it soughted and check your coils.

[xceptional]

I checked the engine earths... well at least the ones I could see attached to the engine bay. I could find only three. One attached to the ECU mount, one just behind the left headlight under the air filter box and the other behind the right headlight under the battery. None of them look substantial. The ones behind the left headlight looks like headlight earth and the one behind the right headlight disappears into a loom that appears to go to the fuse box. I could not see anything else (mind you it was in the garage using a torch) but nothing appeared to come away from the motor down low and attach to the engine bay. Anyway they were all tight however I sprayed some WD40 on them to ensure there was no moisture present. The battery terminals were securely terminated.

I thought I would check over the motor for some obvious lose items and found that the clamp fastening the cross-over pipe to the throttle body was very lose. The clamp could be freely twisted around the the hose. I have read of others experiencing less than satisfactory engine performance due to incorrect air/fuel mixture caused by lose plumbing. I'll see if that made a difference when I first stat the car tomorrow however I'll need some pointing in the right direction for engine earthing strap locations to complete a comprehensive check thanks guys.

Cheers

[xceptional]

Well, nothing has changed since the engine earths where checked (ones I could find - see above post) and the throttle body clamp tightened. In fact it was probably worse this morning as it was both cold and wet.

Unfortunately the next thing to do is the coils unless any has any other ideas.

Cheers