MA61 5ME not smooth over 4000RPM. sounds like limiter bashing?

[patrickleslie]

Hi all,

My 5ME MA61 does this odd thing where if you floor it higher than 4500rpm (usually around the 5000rpm mark, sometimes earlier) it will start to run way unevenly and there is a significant loss of acceleration power.
If you ease your foot down and push gently through the 5000rpm band it doesn't do it as badly, if at all (but who eases gently through 5000rpm lol). Doesn't seem to do this when free revving/not in gear. Doesn't really do it if you downshift, heel and toe, and start at higher than 5000rpm. When it does happen the exhaust makes a noise that sounds a bit like limiter bashing (or engine-braking style back firing in the exhaust (which is cool I guess? :/ )), but I'm 99.94% sure that a 5ME doesn't have a limiter, let alone at 4500RPM. Because of this I struggle to hit 95km/h in 3rd gear, 4th is maxing out at at 118km/h, which doesn't give 5th a leg to stand on when you shift up (GPS speeds, not speedo).

I have 3 theories but nothing solid to go on yet:
- Exhaust (Looks to be standard manifold with a custom pipe to muffler from a previous owner) is too small and is restrictive, there is to much flow from the engine, end result is no good.
- Car runs too rich on fuel (except that I average 10.2L/100 country, 13.9L/100 city which isnt too bad for its age?), and it is backfiring and sucking the power
- There IS a limiter on the car and it is malfunctioning or something weird.
(and "this would be impossible but whatever" theory 4 - Tacho is wrong and what i think is 4500 is actually 8000. This doesn't make sense because the RPM matches the speed which mostly matches the gearing...)

Now I don't expect to break any top speed records in this 30 year old car but seriously, a Supra that can't break 135km/h without a gentle 10km run up is a sad Supra
If anyone has some tips or past experiences with this (or something similar in other cars) that would be great info to pass on, cheers!

[CrUZida]

High RPM/load breakdown is normally caused by shitty leads/plugs/dizzy cap/rotor, or maybe a blocked fuel filter.

Start there.

[patrickleslie]

Plugs were changed at the initial service it had after i bought the car, wouldn't even be 10,000km old yet...honestly can't see these being the problem but it wouldn't hurt to check i guess!
Fuel filter is clear and I do have a spare lying around somewhere so that's no worries


- Leads are visually 'new' but they could be shit quality ones. It might be worth mentioning then that when I run high beams, the stock fog spotties, and full heater the dash lights will flicker and completely turn off if you do one more electrical thing like braking (lights) or power windows. The engine never seems to be bothered by this (I assume due to fuses and such) though so it wasn't high on the priority list to worry about.
- Didn't think to check the dizzy
^ I'll try those two tomorrow, cheers Cruzida

[CrUZida]

The dash light issue is common, mine used to do that. Shouldn't affect the motor (but check the earth between the battery and the body).

Also check the air filter, if its collapsed it will breathe fine at low rpm, but create a blockage at high rpm.
Exhaust blockage, while possible (collapsed muffler/etc), would be pretty unlikely, and you'd probably hear it.

Also, depending on your leads, if they are touching they can crossfire, and the engine will misfire at higher loads. I've had this before.

[swb982]

take out your spark plugs and check....

Ignition coil ???

Spark Plug leads ?

check your AFM ? is it clean or clogged with crap... ? Have you changed the AFM settings at all ?

[patrickleslie]

RE Dash lights I already added a second ground wire, didn't change anything except now I can run high beams before it flickers instead of low beams

Stock AFM ... At least, unmodified by me. I'll pull apart the whole intake piping and check it's not clogged!
Air Filter was replaced before a trip to Melbourne two weekends ago, old one was dirty but ok, this 'limiter bashing' was happening before and after that so i can rule that out.
Leads could definitely be cross firing, it's a mess under the hood. I'll rearrange them and see if there's a difference.
Didn't think to check ignition cool either

Thanks for the tips

[Screamn_Sleeka]

Sounds like fuel pump is failing to give full pressure at high load. Try replacing it.

[patrickleslie]

http://youtu.be/swHYGPQzvOA

Short vid trying to show what is happening and when. Listen with headphones so you can hear the exhaust change a bit clearer. Ignore the speedo, it's pretty out due to my tyres, reads 119 at 110.

Thanks for the pointers so far everybody

[HMI265]

Sounds like fuel pump is failing to give full pressure at high load. Try replacing it.

my RA65 had the same symptoms at far lower in the rev range and this fixed it (kinda scary feeling on a fresh rebuilt motor). Check the fuel pressure regulator too.

[patrickleslie]

Checked a whole bunch of stuff yesterday. Basically ruled out anything electrical, so it is most probably the fuel related as a few of you have suggested. This leaves fuel pump, filter (to be swapped out tonight), poor fuel pressure (blockage or something), or the mixture is wrong.

[neal]

Their Dissys are known to fail as well.

[swb982]

Just a thought are the fuel lines ok ?? I know I've found a few cracked lines around the engine ???

suggest as first, replace the fuel filter and see if that changes anything..... if not, then, fuel pump.....

[patrickleslie]

Here's the old filter that's been on the car from the previous owner...


A short test drive after and the problem is still there
I guess a new fuel pump is in order?

[swb982]

bugger...... did you check for worn/cracked fuel lines ?

[patrickleslie]

Apart from a bit of splitting at the filter ends (caused by the clamps) the lines look ok. I can't see any evidence of leaking fuel.