Here’s one of my crazy longshots. A car needs to breathe freely. A clogged exhaust or plugged catalytic converter will make it hard to “exhale”. But on the other hand a clogged intake will make it hard to “inhale”. I recently had a situation where mice had built a massive nest at the air filter. The fact that it happens at higher speeds when there is more air demand kind of indicates that it’s having “breathing” difficulties.
Anyway, as I say, this is a longshot but it’s a quick and easy look-see.
I’ll explain the exact scenario after I have replaced my spark plugs. I get in my car in the morning, turn my key and hold it for 2 seconds. Engine starts the fails the first time(every time I start cold engine) then the second time it takes 5-8 seconds to turn over. Once it has started the engine is in idle and reveal between 250-500rpm(on it’s own) I leave it until the rpm settles at 500 then give it a little rev to get it heated up for around 5-10 seconds then pull off. Pulling off in first gear no matter how much gas I give the car it takes around 3 seconds before it gets to 3000rm where I usually change into second. Then after 1st gear when I put my foot half down it is the same as my foot to the floor. Going up slopes (anything above 5%) the car physically does not have enough power to stay in high gears. The car slows down to 20mph where I have to switch to 2nd gear because third won’t get me up. Down hill works perfectly fine like I expect the car to be at all times and flat roads take like 1 second per increase in 1mpg (every 10 seconds I can accelerate to 10mph higher) it usually takes around 25-30s before I’m at 3000rpm in 4th so I can change to 5th.
Notes that might help.
It’s impossible it reach 60+ on flat roads
Only time I can reach 70 is down hill on motorway.
My petrol intake is around 35L per week for 250 miles driving before it’s empty(extremely expensive £40-50)
When going fast I feel the car judder, nothing serious but light enough to notice
I have put the car in neutral going at 60mph and the car runs without juddering so I presumed that the juddering was caused by a misfire.
If I ever go above 3200rpm I start to smell burning, not sure if it’s petrol or oil or what but it’s not natural.
Sorry for the length. Just tried to make it as in depth as possible so you guys could get an exact idea.
At the start I say revels, I meant revs automatically( without me touching anything after I have turned the key and let go)
db4690 is correct, you should pay them for diagnosis first before making assumptions. If it is a plugged cat, they should be able to figure it out. MY 2 CENTS is also correct that an intake restriction could cause similar symptoms.
Did you check out what my 2 cents said about checking the air intake for mice or junk? I rented one of those over there and it always was at about 3000 rpm on the highway. Don’t know if it was a 3 cyl or not. I liked the car though but around here its closer to 2000 rpm at 70 mph.
I’m going to take it to a garage today or tomorrow and get it diagnosed. Hopefully it’s nothing too expensive to fix like a problem with the engine.
Update: I took the car into a garage today and they plugged into a little diagnostics tool, they said the tool was telling them it was the Mav sensor or something and the mechanic also suggested that I should replace the coil pack aswell, should have them both done sometime tomorrow. Hopefully this will be it fixed, sick of this car being shit.
MAF = mass airflow sensor. That’s good news, should be cheap fix.
Would that be the problem of there not being a difference in acceleration from the foot being half down compaired to fuly down ?
Maybe. If the MAF is faulty/dirty, it may not be able to sense the difference in airflow between half-open throttle and full-open throttle, and the computer wouldn’t inject more fuel.
Of course, you could have both a faulty/dirty MAF and a clogged cat that the mechanic hasn’t found yet…or possibly a clogged fuel filter…
I’ll get back to you tomorrow when the new one is fitted and tell you if that was the problem or not
@jayjonny96
On the one hand, you could very easily replace the MAF sensor and the coil pack yourself, and save money
On the other hand, if the shop’s diagnosis is wrong, they’re on the hook, so to speak
I’ve had 3 or 4 bad MAFs. All but one pretty much shut the car down, would idle but anything much over 20 mph was impossible. Acted just like a fuel issue/restriction, so yeah that could be it. On the other one, it would just run rich. Good luck.
Replaced the coil pack, no difference, so they took it back out and didn’t charge me for it, replaced the maf sensor no noticable difference except that it doesn’t come up on the diagnostic tool anymore. What would you guys suggest. I also got told that my idol rpm is lower than usual and the mechanic said something about there being a bad throttle body
Everything still points to a restriction in the intake or exhaust. Ask your mechanic if he checked the air filter box for mouse nests, etc. If he has, next step is to check the catalytic converter and/or muffler for flow restrictions. The muffler could also have a mouse nest or collapsed baffle restricting flow.
The low idle could also be a result of the flow restriction. Throttle body may be OK. Sounds like your mechanic is just guessing now.
They can screw in a gauge and check back pressure on the exhuast. It would tell them if the cat or muffler is bad. Have they checked fuel pressure? If not, I would do that too.
I’m going to take it to a different garage tomorrow to see if someone else might be able to do it. I asked about checking the compression but they did not have the equipment for it. MOT is due at the start if December, hopefully I get it fixed and the mechanics guess on the throttle body replacement/ cleaning was because that every time I lift my foot off the gas at high revs it makes a rattling nice for a seconds or so.
Has the fuel filter been changed yet?
Have them check the fuel pressure.
How did the plugs look? Dark or light?
If there is a rattling noise when the accelerator is released from a fast idle you need to quit worrying about power loss until you can confirm that the bottom of the engine is not about to let go. A loose rod bearing, i.e., rod knock, as in Rod Knox, is a likely cause and the engine would need to be removed and rebuilt. If the pan can be removed easily doing so would give access to the bottom end and it might be worthwhile to do so. Of course a well experienced mechanic would quickly recognize the noise and know the likely cause.
I’m wondering if the rattle is from loose debris inside the cat. More info on diagnosing a bad cat here: