excessive fuel consumption and relay oddities

Roadrunner · Postby **Roadrunner** » Wed Aug 07, 2013 2:40 pm

My SE is having a few hiccups lately that I am hoping can be resolved here.
It appears to be more engine related than turbo related so i'm posting it in here (please move to the turbo forum if appropriate)

So here goes:

Originally stock SE, had a full 2.5inch dump + exhaust put on at MX5Mania. Has been solid as, insane increase in power over stock and on boost a lot earlier. ear to ear smiles, absolutely loved it.
Note: at this time I installed an amplifier in the boot (more on that soon)

2 weeks later started getting heavy misfiring under load and at takeoff. Replaced spark plug and leads and that fixed all that up to a degree.

Since the plugs and leads were replaced the car ran smooth but when coming into boost there wasn't really any more power.
It was like an NA but showing 7psi on the gauge. there was no big rush of power.
Due to being busy it stayed like this for 2 weeks.

When I got around to it, I checked for fault codes, there wasn't any codes but I disconnected the battery to reset the computer and took it for a drive and BAM there was the power!
I thought brilliant! All sweet, but then 25mins down the road, coming out of a roundabout pushed the throttle hard in 2nd and it bogged down.
Eased off, drove it back home and it seemed to run perfectly fine.
Took it to a friends house and at about the 20minute mark it was idling fine but as soon as I touched the throttle it spluttered till I gave it about 2000rpm and then it drove fine (cruising speed around town) (kept it off boost during this time)

When I arrived idle was near perfect, but one touch of the throttle it spluttered. During this time we noticed that there was a fair bit of moisture (Fuel? didnt smell like it) coming out the exhaust.
Something I noticed at this stage is that the Sensor Boost (relay?) was not ticking when we moved the throttle, yet it was earlier in the day when the car seemed to be running fine.
Again, no engine codes

We Shut it down and left it, came back the next day and decided to disconnect the amplifier (after having read up all about earth loops) and it ran perfectly all the way home (25 minutes).
Before I left I listened to the engine idling and revving and there was an audible click come from the Sensor Boost relay when touching the throttle again. everything seemed ok.

Drove it to work twice (1 hour each way in high speed plus stop start traffic) and it was running fine (no spluttering at all). Power was there on boost, albeit sometimes it felt a bit lacking, but now I am noticing i'm chewing through fuel.
The exhaust is making a lot of gurgling sounds at full throttle as well as when engine braking/coasting down towards a red light.

So I guess I have narrowed it down to this:

- Iv narrowed it down to an electrical issue or sensor dieing?
- Is it coincidental that when I disconnected the amp that most of the issues went away, or could this have damaged a sensor?
- Should the Sensor Boost relay make a clicking sound as soon as the throttle is moved?
- The increase in fuel consumption and the exhaust almost always making a gurgling sound makes me think its running rich (the bogging and spluttering caused by too much fuel in the system?)
- If its a sensor, why dont I have a CEL? Would a slowly dieing intermittent sensor not throw a code?
- Was thinking maybe o2 sensor but the one place it does run fine the entire time (except the fuel consumption) is part throttle when the o2 sensor is being used for AFR (my understanding is on full throttle the computer ignores the o2 sensor??)
- slowely dieing TPS sensor? (we disconnected this sensor and started the car, idle seemed okish but spluttered when throttle touched, almost the same as the problem I had the previous day. This also put the CEL on as soon as the car started. reconnected the TPS and cleared the code, no codes since.

Any suggestions before I start throwing new sensors at it?

Roadrunner · Postby **Roadrunner** » Wed Aug 07, 2013 2:56 pm

Wow thats a bit of an essay! Sorry about that!

manga_blue · Postby **manga_blue** » Wed Aug 07, 2013 3:47 pm

Get a leccy to check the alternator output.

Roadrunner · Postby **Roadrunner** » Wed Aug 07, 2013 3:58 pm

Will do.
That actually makes sense in regards to the issues when the amp was connected, as its quite powerful.

How long do alternators usually last before they go kaput?

manga_blue · Postby **manga_blue** » Wed Aug 07, 2013 5:42 pm

How long is a piece of string?

The symptoms you've got might be explained by low voltage at coils and injectors. Weak alternator is one cause. Wiring problems, especially weak earths, are another. Did you play with earth straps when you installed the amp?

Roadrunner · Postby **Roadrunner** » Wed Aug 07, 2013 5:46 pm

No didn't change anything factory wise.
Simply hooked amp power straight to battery and earth to a bolt in the boot.

project.r.racing · Postby **project.r.racing** » Wed Aug 07, 2013 11:11 pm

sounds like a dieing alternator or battery or both.

Roadrunner · Postby **Roadrunner** » Thu Aug 08, 2013 9:36 am

Will try to get an auto elec to test the alternator and battery tomorrow.
Does make sense, sincethe problems came and went with the amp.

Also going to replace the O2 sensor as well for the sake of it, as the car has 105,000ks on it and there's no records of the sensor being replaced.

Roadrunner · Postby **Roadrunner** » Sat Aug 10, 2013 9:50 am

So the alternator checked out fine, but the battery was apparently at the end of its life and also had a very low rating?
So it's been swapped out for a more powerful battery and everything seems to be ok.
Amp is hooked back up and so far no dramas.
Will keep an eye on it but this seems to have fixed everything up (and the car fires up a bit better too now)

Thanks fit pointing me in that direction, I would have been swapping out sensors spending a fortune and never have though of the battery!

project.r.racing · Postby **project.r.racing** » Sat Aug 10, 2013 11:41 am

great to hear.

Roadrunner · Postby **Roadrunner** » Mon Aug 19, 2013 9:32 am

Just a follow up.
In the end the battery made a bit of a difference but wasn't the real cause of the problem (I think the reset of the ECU with the battery change made it ok to drive but the problem came back)

In the end it was a dirty "Sensor Boost" sensor, as well as the EGR vacuum solenoid (that connects to the Sensor Boost)

Cleaned both of these out with electrical contact cleaner and a can of air, as well as the little air filter on the solenoid and I have full power again. Very smooth idle and power comes on strong, nice and early like I remember!
Drove it to work twice and then a big 250km round trip on the weekend with lots of hard pulls and cruising and didn't hick-up once.

Very happy boy!