Acceleration Problem

YipYipU

Hi all.

Hoping someone can help me out here. I have a 98 Mazda Xedos6 (2.0 petrol V6). When accelerating there seems to be a number of flat spots between 2000 and 4000 rpm. I have only just serviced the car, changed oil, filters, spark plugs, cleaned the air flow, checked all pipes but the problem seems to have remained. Has anyone any ideas what this might be or is there anything else I can try myself before forking out a fortune get to the root of the problem?

Any advice will be greatly appreciated.

Thanks in advance.

Yip

Plug

It could be the fuel pump. I'd do a fuel pressure test before I start replacing anything, also get any faults read that may be there.

YipYipU

Thanks Plug. I'll try get my hands on a fuel pressure gauge and get someone to check the electrics on the pump. If the pump needs to be replaced would it be a big job?

johndaman66

Ignition coil I wonder?

That symptoms you describe would be consistent with (among other things) an ignition coil pack thats on the way out.

YipYipU

The fuel pressure and fuel pump have proven to be ok.

How does one know if the ignition coil pack is on the way out? I have priced this from Mazda and it's €364 + VAT. Though I have located one on eBay in the UK for €28 + pp.

Should I just get this and replace it and hope it does the trick?

no1beemerfan

Is there any air leaks anywhere, loose/split rubber hose? Could be a coil pack also.

johndaman66

YipYipU wrote: »

How does one know if the ignition coil pack is on the way out? I have priced this from Mazda and it's €364 + VAT. Though I have located one on eBay in the UK for €28 + pp.

Should I just get this and replace it and hope it does the trick?

Ouch, thats bloody saucy! If I recall correctly I paid about €100 or perhaps a little over for the ignition coil pack when it gave up on my Vectra some time back. I think it was plugged into the diagnostics that time and it highlighted the fault but I stand to be corrected on that one. Of course some know how to charge well for the diagnostics too but you may need to bite the bullet. I'd be very hesitant about getting parts that are that expensive in the hope they are the problem. You could end up being seriously out of pocket and the car driving no better.

Serious difference between Mazdas price and ebay but I do feel you are taking a chance in buying car parts of ebay too. Theres the option of buying one from a breakers yard but thats hit and miss too. It may end up being no better than the one you took of.

YipYipU

Well I've no intentions of forkin out €364 to Mazda but I'm thinking I might just take on chance on the one on eBay. The seller has 100% positive feedback for the last 12 months and has a feedback score of 29322. I had a quick look through and some of the feedback is for similar coil packs. They Also don't normally ship internationally but I emailed them about this and they were quite happy to make an exception. I think I will take a chance on it, especially since having checked partfinder.ie there appears to be a massive zero V6 Xedos' for breaking in Ireland.

YipYipU

Forgot to mention, the coil pack from eBay also comes with a 12 month guarantee.

Richie ae86

sounds like your fuel filter, they are supposed to be replaced every 2 years but noone does, id change that they are only around €12 mark, hope this helps

Wheelnut

YipYipU wrote: »

.., cleaned the air flow, ...

Do you mean you cleaned the airflow meter? This is not a service item. The airflow meter is a very delicate item and easily damaged. If you had no problem before the service then you may have caused some damage to the AFM.

Tea drinker

Wheelnut wrote: »

Do you mean you cleaned the airflow meter? This is not a service item. The airflow meter is a very delicate item and easily damaged. If you had no problem before the service then you may have caused some damage to the AFM.

No, he said the problem REMAINED after the service, including this cleaning. EDIT : though this cleaning does not eliminate it as the fault...
I'd check all vacuum connections, but I don't know much about the reliability of these coilpacks, maybe they fail frequently. e364 seems an *awful lot of money* for a coilpack though.
Would be great if you could get a loan of a coil pack and rotate it through the differnt cylinders, see which pack was bad if any. And check the connections are nice and clean while you're at it.

YipYipU

Ok so here's what I've tried so far.
I began by doing a fuel pressure test and had the fuel pump checked, both of which seemed to be fine.
I replaced the fuel filter and also I took a chance on the replacement coil pack from eBay. Still no better.
Someone suggested I clean the distributor cap, so I did. It had quite a lot of dirt built up on it. I was hoping this would be it but unfortunately it hasn't made the slightest bit of difference. To the best of my ability I've checked all hoses are securely in place and can't find any holes or splits anywhere.

I'm all out ideas at this stage. Can anyone give me any more suggestions?

Thanks again to everyone for their suggestions, greatly appreciated.

Mar4ix

When did you change timebelt ?? if it slipped by on teeth, it could cause similar problems.
quiet a lot to be done, check and clean throttle body, in night time start car, and check is there any spark leak from sparkplug leads, examine distributor cap and head ... if any cracks in there, ... i think not expensive to buy new one.... make sure in air pipe, which deliver air in to inlet manifolds, no any leaks, or crack, sometimes it may be underneath , and you cant see or feel.

As you did quiet a lot of tests and checks, now need dig deeper....
Check cylinder compression, make sure coolant liquid is in good shape, could worth bring to garage, and check is headgasket ok (perform chemical test on coolant liquid, if there is leak in headgasket, sample change colour with some chemicals).

try address your question in mazda forums, id say uk one... there some people have more experience too ....
could be just one sensor fault ....

Good luck , and let us know how you keeping.

Wheelnut

YipYipU wrote: »

...and also I took a chance on the replacement coil pack from eBay. Still no better.
Someone suggested I clean the distributor cap, so I did. It had quite a lot of dirt built up on it.

Not sure what you mean there, it's unlikely to have both a coil pack and a distributor. The coil pack consists of a group of small coils that go directly on to the spark plugs, one for each plug. They are switched individually by the ECU and don't require a distributor. If it has a distributor there will be only one coil and the high tension current from it is directed to each plug in turn by the distributor. Also if it has a distributor it's the inside of the cap that should be cleaned and checked.

maxamillius

+1,

cant have distributor cap and coil packs,two completely different parts!so you might wanna check what you have first before ya fork out a load of cash!

YipYipU

Wheelnut wrote: »

it's unlikely to have both a coil pack and a distributor.

Thanks Wheelnut, perhaps I've been misinformed. I cleaned the inside of what I was told was the distributor cap. I've taken a couple of pics of the parts in question.

This is what I cleaned (inside), it was a pain to open it up so didn't bother doing it again for the sake of the picture.


And this is the part I replaced.


They are connected to each other by the blue cable which can been seen in this pic.

YipYipU

Mar4ix wrote: »

When did you change timebelt ?? .......................
try address your question in mazda forums, id say uk one... there some people have more experience too ....
could be just one sensor fault ....

Thanks Mar4ix. Timing Belt was changed less than 2000 miles ago, just after I bought the car. I'll check out the mazda forums again, I have looked through some already but couldn't find anything relevant.

maxamillius

thats is the distributor cap,the blue lead is leading off to your ignition coil!have you taken the distributor cap off and checked for cracks and dirt?

maxamillius

small hairline cracks can open up when engine runs hot,this causes the spark to get lost therefore causing misfire and acceleration problems and loss of power!

YipYipU

So it's Ignition Coil not Coil Pack is that correct? Yup I took off the cap, cleaned it with a small brush and put it back on. It was pretty dirty, didn't seen any cracks.

YipYipU

maxamillius wrote: »

small hairline cracks can open up when engine runs hot,this causes the spark to get lost therefore causing misfire and acceleration problems and loss of power!

Maybe I should take it off again and examine it more thoroughly. I have noticed that it doesn't seem to happen when the engine is cold.

maxamillius

check for cracks even the smallest of crack can cause what appears to be a huge problem!have you checked your spark plugs?

maxamillius

try post a picture of inside the cap when you take it off!

YipYipU

I'll check it again so. Yup there were new plugs put it in less than 2000 miles ago. It'll be tomorrow when I get to do it so I'll post some more pics then.
Thanks

maxamillius

also are you sure you have the leads connected in the right order to the cap?

YipYipU

Well they're in the same order as before I took them off the cap. I made sure to label them before removing them. Unless the previous owner had them in the wrong order. Any way of knowing the correct order?

Wheelnut

@YYU: The bit in the first picture is a distributor cap and the bit in the second is a coil, but I think you know that now.

I would like to highlight what I'm about to say by marking the pics but I can't do it, so try to follow and apologies in advance:

In the first pic there is something that looks like a plug lead hanging down at the face of the distributor cap. Check if this is connected to anything, if it is loose it could be your problem.

In the second pic it looks like there is a bolt missing from the front of the air duct. If the hole goes right through to the inside, the airflow through the hole could upset the air-flow meter.

Finally you say the plugs were changed 2000 miles ago. This is a transverse six cylinder engine (right?). The plugs on the rear three cylinders are a pig to change and it involves removing the manifolds. It's conceivable that a lazy mechanic would not bother and just leave the old plugs in. It might be worth checking it out.

maxamillius

In the first pic there is something that looks like a plug lead hanging down at the face of the distributor cap. Check if this is connected to anything, if it is loose it could be your problem.

agreed noticed that myself looks like its not connected to anything!

In the second pic it looks like there is a bolt missing from the front of the air duct. If the hole goes right through to the inside, the airflow through the hole could upset the air-flow meter.

again well observed mate could well be causing air flow problems,worth checking!

Mar4ix

there must be 2 coils and 2 distributor caps each have to have one lead from coil and three sparkplug leads) , in these pics we can see only half of engine ignition system.

Wheelnut

there must be 2 coils and 2 distributor caps each have to have one lead from coil and three sparkplug leads) , in these pics we can see only half of engine ignition system.

I think you'll find the other three connections on the bottom (out of sight)

Tea drinker

the lead from the coil looks dirty. Remove it, clean it thoroughly and check for damage. Clean all around the outiside of the coil, maybe remove it to inspect/clean.

replacement HT leads would be maybe 30-40 euro in a motor factors assuming the 7 of them. They have various lengths and connectors available usually.

use plenty of rags when cleaning the dist cap, and never use scrapers or sandpaper.

YipYipU

Wheelnut wrote: »

In the first pic there is something that looks like a plug lead hanging down at the face of the distributor cap. Check if this is connected to anything, if it is loose it could be your problem.

This lead is not connected to anything at either end. I'm assuming the blue cable replaced this in the past and it was just never taken out. It's now out. There are 7 cables connected to the cap, 6 of which go to the plugs and the 1 remaining goes to the coil.

Wheelnut wrote: »

In the second pic it looks like there is a bolt missing from the front of the air duct. If the hole goes right through to the inside, the airflow through the hole could upset the air-flow meter.

I had checked this before but the hole doesn't go all the way through so no air is getting in through there.

Wheelnut wrote: »

Finally you say the plugs were changed 2000 miles ago. This is a transverse six cylinder engine (right?). The plugs on the rear three cylinders are a pig to change and it involves removing the manifolds. It's conceivable that a lazy mechanic would not bother and just leave the old plugs in. It might be worth checking it out.

I had done the front 3 myself but couldn't reach the back 3 so asked him to do it for me. This concerns me now as I had never used this mechanic before, though he was recommended by a friend. I guess I'll just have to take his word for it right?

YipYipU

Wheelnut wrote: »

I think you'll find the other three connections on the bottom (out of sight)

Yes the other 3 are underneath.

YipYipU

Tea drinker wrote: »

the lead from the coil looks dirty. Remove it, clean it thoroughly and check for damage. Clean all around the outiside of the coil, maybe remove it to inspect/clean.

Thanks, I'll give it a go.

Tea drinker wrote: »

use plenty of rags when cleaning the dist cap, and never use scrapers or sandpaper.

I have already cleaned inside the cap using a rag and a soft bristles brush. I will be removing it again tomorrow to re-inspect it for cracks.

Thanks again for all the help folks.

Greyfoot

Coil leads can be "tested" by removing them from the spark plugs and holding them say 6-8" from the body of the car and turn the engine over.(be careful not to touch the body as electric shock can be painful)
If there is an arc then the given coil is ok.

Wheelnut

YipYipU wrote: »

... inside the cap .... I will be removing it again tomorrow to re-inspect it for cracks.

You will not find cracks as in the normal sense. What you are looking for is evidence of a phenomenon called "tracking" in which the HT current flows across the surface and goes somewhere useless. It leaves a mark that looks like it was made with a pencil so it will be difficult to see on a black cap. Often the tracking will be between two of the electrical contacts, but it will always start at a contact wherever it goes.

Greyfoot wrote: »

Coil leads can be "tested" by removing them from the spark plugs and holding them say 6-8" from the body of the car and turn the engine over.

I think you mean 6 - 8 millimeters, not inches. This old method is not to be recommended on modern cars with computerised electronics. A high tension spike in the wrong place could make sh*t of an expensive ECU. (Besides, doing it your way will leave nasty scorch marks on the bodywork)

maxamillius

You will not find cracks as in the normal sense. What you are looking for is evidence of a phenomenon called "tracking" in which the HT current flows across the surface and goes somewhere useless. It leaves a mark that looks like it was made with a pencil so it will be difficult to see on a black cap. Often the tracking will be between two of the electrical contacts, but it will always start at a contact wherever it goes.

hairline cracks can very easily appear which over time become bigger,when engine runs hot crack can open wider and spark will get lost!saw it on distributor cap last week!

YipYipU

Ok so I have the cap off again now.

Wheelnut wrote: »

You will not find cracks as in the normal sense. What you are looking for is evidence of a phenomenon called "tracking" in which the HT current flows across the surface and goes somewhere useless. It leaves a mark that looks like it was made with a pencil so it will be difficult to see on a black cap. Often the tracking will be between two of the electrical contacts, but it will always start at a contact wherever it goes.

I'm not really sure where I should be looking for "tracking". In the following pic there appears to be a number of marks which look like pencil marks. Is this what you are referring to or would it be on the cap itself?
The cap itself is spotless now and there appear to be no marks or cracks whatsoever.

kermitpwee

Those flat spots are caused by your throttle position sensor I reckon.

Wheelnut

The second pic shows the inside of a black cap and it looks perfect to me, so that's not your problem. I presume there's a rotor arm somewhere (not in pic) and you should check that for tracking. It's less likely but I've seen it happen.

I think you have illiminated the ignition system (although I'm not sure how we became so focused on it in the first instance). Do the flat spots happen at the same revs every time or can they happen anywhere between 2000 and 4000 revs? If it's the same every time it might point to Kermit's suggestion.

Mar4ix

somebody said, there cant be coilpack and ignition distribution system in same time ....

YipYipU

The feckin' thing won't start . I put the cap back in place and started it up. It ran fine for about 10 seconds then cut out and wouldn't start anymore. I took off the cap again to make sure everything was in place and it was. I labelled all the leads before removing them so I'm sure they're all in the right place.
Should I just give up and call a mechanic?

Tea drinker

That's weird. And a right bloody p1ss off!
Maybe just go over the connections (especially the low tension and high tension to from the coil) again to make sure they are 100%. Perhaps some adjacent connector got loosened?

Hard to say anymore, but you might be right on getting a mechanic to look at it. What you did before as regards cleanign etc looks 100%.

YipYipU

Gonna give it one more try this evening when I get home. If it doesn't work out I may get onto the mechanic.

For the cleaning I just used a rag, a small soft brush and some cotton buds. Seemed to clean it up nicely but unfortunately didn't solve the problem.