Help - blacktop going flat under load

[Ninja25t]

I recently had an issue with my BZ-R levin messing around under acceleration. It was throwing a TPS fault code, and my auto electrician couldn't find any other problems, so we replaced the TPS. While this has certainly sharpened the throttle response, and is no longer throwing a TPS fault, it still has the same problem under load.

The main symptoms are that once the car is warm (takes ~30-40 minutes of normal driving) it intermittently goes flat and won’t accelerate under anything other than light load/throttle opening. I can drop gears and it will hold higher rpm but again only under light throttle. If I hold it at the point where it goes flat it sometimes feel like it is surging slightly (not as harsh as a miss) and will occasionally pick up slightly.

For background the motor has less than 10,000 km on it from full rebuild so its unlikely to be a mechanical problem (never say never!). It also starts and idles and cruises around without issue and is no longer throwing any fault codes. The coil and leads are new, plugs weren't replaced as they only had about 20,000 km on them and looked fine at the time of the rebuild. Anyway it feels like a fueling issue rather than electronic to me, but the fuel pump is apparently testing OK, although nearer the bottom end of the specs. Only the fuel filter was changed during the rebuild.

Has anyone experienced and fixed these sorts of symptoms or have any suggestions? My auto sparky is suggesting an ECU fault, but I had it apart a couple of months ago and it looked sweet, none of the usual capacitor problems at least… so I'm still leaning towards fueling. But as nothing is obviously out of spec or throwing a fault code I would like to try and narrow the field before I commit to pulling the fuel pump or ECU etc.

Any thoughts appreciated, cheers.
Shane

[85AW20v]

If it's taking 30-40 minutes to warm up try replacing your thermostat - it could be stuck open. Temp sensors would then think engine is still cold and would be fueling it to suit the cold engine rather than warm. Also check the temp sensors are operating correctly - I think there's two or three of them.

[Ninja25t]

Sorry I didn't explain that very well, I meant it only happens 30+ minutes after its warm. It comes up to temp normally. Cheers

[Kiwi-Corolla]

Sounds a lot like an oxygen sensor problem. Try unplugging it from underneath the car and see if it solves the problem.

[edwagon]

Exhaust blockage?

I had an h22a Accord a while back that was as sweet as a nut until it had been running for 5-10mins, and would then quite distinctly go 'off' and lose all its torque, but as you describe would kinda 'catch' now and then if I back-pedalled it. It was a pig of a thing.

Felt like it was starving for fuel but nothing I did helped. I.checked.EVERYTHING

It was in for a new exhaust anyway so I went ahead and made up a new system, to give myself a break from struggling with the cause of the flatness

Voila!

Problem went away

Exhaust blockages/restrictions cause all sorts of strange behaviour - they cause across-head restrictions which messes with the MAP signal etc and can be hard to recognise

Can someone loan you a manifold-back exhaust system for a 60minute drive?

[Crucible]

Either a plugged exhaust or low voltage from map or maf imo.

Tee in a vacuum gauge
should have a steady 16" @ idle.

If it is a fair bit lower remove the O2 so it can breath and take for a drive to see if it improves.

[matt dunn]

I had a celica doing similar things a while ago,
Checked all sorts of stuff and found the map sensor voltage would rise as expected when the throttle was opened,
but would drop back to showing vacuum again with the throttle still open.
Tried map sensors and stuff,
in the end it was a faulty pod filter, It must have been blocked of not flowed enough air,
as it looked ok and was not obviously dirty, but without the filter the car ran better and would rev.

[Ninja25t]

Thanks for all the suggestions but the problem now appears to be FIXED! (hopefully...)

It appears that the ECU water temp sensor was playing up. One morning last week it went from messing around to running like a total bag of shite. I checked the codes again once I got to work and it was throwing TPS (again) but with water temp sensor also. It hadn't thrown that code before despite playing up for weeks and both myself and the auto sparky checking several times and running all sorts of checks/tests.

Anyway, replaced the water temp sensor over the weekend and it has been running sweet since (fingers crossed it stays that way!).

Cheers,