4Age Will Not Rev

[rallydad]

Hello all,

 

First time post, long time reader.

 

I have AE71 with JDM 4AGE bigport conversion. Car is running and driving fine except for a problem with the revs.

 

I have checked fuel pressure it is a steady 40psi through surge tank setup with over 3 litres/minute flow through upgraded 8mm feed and 6mm return.

 

Wiring has been completed using posts on this site and apart from a couple of little hiccups initially it fired up pretty much straight away. Thankyou to those who provided the knowledge!

 

It has new coil, plugs, leads, dizzy cap and rotor.All of which were cross referenced at time of purchase to make sure they were the right ones. All earths have been cleaned and I have added a direct earth into the ignitor body. It also has the oxy sensor installed with shielded wire to the ECU to eliminate static interference.

 

The problem is I can get a full 7,700 rpm out of the engine while it is warming up (not under load) but once heat starts to build in the engine and ignition system the revs drop back to around 5,000 max. The ignitor becomes very hot to touch (not mounted near heat source) and the dizzy also gets super hot as the #1 header pipe runs directly underneath.

 

I intend to fit some heat shield/wrap to the headers asap but i suspect this is not the cause of the problem.

 

I have calibrated the TPS (thanks again to rollaclub members) using the specs on this site. Ignition and cam timing is spot on.

 

Wiring is a tidy splice of 4AGE engine loom into AE71 body loom. No pinched wires.

 

New alternator putting out around 13.5 volts.

 

I have built cars before but this is my first EFI conversion and I am stumped. I THINK i've narrowed it down to either the ignitor or the dizzy but unsure if these components slowly fail or just stop working suddenly if they are stuffed.

 

The spark seems weak when tested at spark plug lead.

 

Ignition timing tested with light at point of revs breaking down sees it come back to around TDC (this is limp mode?)

 

There is a small oil weep into the dizzy from the shaft seal.

 

I have considered fitting engine check light to ECU however with only 10 or 11 fault codes available i'm not sure whether my problem can be diagnosed by the ECU.

 

Any suggestions from those who may have had this problem would be much appreciated!

 

Many thanks.

[B.L.Z.BUB]

Hook up the check engine light. can't hurt

Edited June 2, 2013 by B.L.Z.BUB

[altezzaclub]

The problem is I can get a full 7,700 rpm out of the engine while it is warming up (not under load) but once heat starts to build in the engine and ignition system the revs drop back to around 5,000 max. The ignitor becomes very hot to touch (not mounted near heat source) and the dizzy also gets super hot as the #1 header pipe runs directly underneath.

The fact that it revs when cold suggests that heat is the problem.

 

Wrap the top 6" of the headers and fit a heat shield. I'm fitting a polished stainless steel case from an old microwave cut to shape, a suggestion from an insulation expert.

 

Add to that a cold air tube taking cold air from beside the radiator to the dizzy & ignitor.

 

An option to engine heat would be a buildup of electrical resistance heat within the ignitor, the only thing I can think of for that would be to swap it for another one and see if the new one gets as hot.. If it does then you're back to deciding if it is to do with the electrics or extractor heat causing it.

 

Running lean would make the extractors hotter than normal, so check the mixture with a mixture display. Perhaps the choke function works when cold to make it run normally, but when warmed up the 'normal' run mixture is too lean.

Edited June 2, 2013 by altezzaclub

[rallydad]

Thanks guys,

 

I agree that heat could be playing a factor here, however, if it is just heat this can be detected as a faulty component by the ECU bringing the ignition timing back to TDC at 5,000 rpm?

 

We don't have any wreckers here with 4age bits and a new ignitor is dear as poison. Unfortunately I can't simply swap bits.

 

I'll fit some heat protection and give the engine light a go before I start spending more cash and let you know how I go.

[ke70dave]

The ignitors do get hot under normal operation, they have some chunky power transistors in them as far as i understand.

 

The distributer should have a little heatsheild under them which would help keep the heat out of it from the extractors, you can see it in this photo (this has no distributer cap on)

 

http://m5.i.pbase.com/u14/aw11mr2/large/38687485.PICT0174.jpg

 

I would also hook up your check engine light and see if any codes are being thrown up, if there is a drama with the distributer signal there is a code for it, the ECU knows what signal it is misses based on what it "thinks" it should be getting.

[rallydad]

OK, so

Running lean would make the extractors hotter than normal, so check the mixture with a mixture display. Perhaps the choke function works when cold to make it run normally, but when warmed up the 'normal' run mixture is too lean.

 

As far as I know the cold start injector runs for about 4 seconds on startup. I disconnected it and no difference to the (non) rev pattern so that one is eliminated.

 

Interestingly when using medical burn spray( makes things cold quickly) on the ignitor once it is hot sees a brief rise in revs. This begs the question is the ignitor knackered? I was under the impression that these electronic components tend to just fail and stop working. Can anyone enlighten me?

 

Too damn cold and dark in the carport to do any more it will have to wait for the weekend.

[altezzaclub]

CRC sell an electronic diagnostic spray for exactly that purpose. Heat changes the resistance in semi-conductors, and chilling them can make them suddenly work normally. They will still work out-of-spec, or fail when hot then work again when cold. My graphics card dies on a hot day when worked hard, but works after a re-start... must cool it one day!

 

Can you chill the igniter with a cool-box and a handful of dry ice? Just a plastic kitchen container cut to enclose it. Mate of mine used to do that when racing, the inlet system was lined with a dry-ice container to chill incoming air.

[rallydad]

Problem solved. Fitted ST162 celica ignitor and heat shield to #1 extractor tube.

 

Here is the original 4AGE ignitor. Note the green round plug removed and a couple of wires chopped. (I was messing around)

Here is the very similar ST162 ignitor installed with a small modification. I tested resistance across the terminals of both ignitors and they were within a bees dick. The wires are the same colour coding but the beige wire from ignitor now runs direct to +ve coil (instead of to different green plug for celica loom) and a bridging wire (brown) from coil +ve to green plug. I have also added an earth to ignitor body (black wires)

Here is the heat shield. The brown stain is the small leak from dizzy. I'll fix that soon.

Here is the now completed engine bay for those who are bothered.

and the car. She now pulls like a train! :thumbsup:

First khanacross next weekend...

 

I hope this helps someone else out there. :yes:

[altezzaclub]

Well done! Could you run the coil on the cambelt cover at the front? or does it take so long for the heat to kill the ignitor it won't matter?

 

Find a stainless steel microwave at the dump and grab the casing. It is so polished it makes a great heat reflector and weighs nothing as a heat shield over the extractors.

 

Good luck for the weekend!

[rallydad]

Well done! Could you run the coil on the cambelt cover at the front? or does it take so long for the heat to kill the ignitor it won't matter?

 

Nah, I reckon the she'll be OK the heat comes from within. Interesting that these continue to function to some degree when worn out. I always thought electronics just stopped.

 

I might fit a heat sink to the ignitor body just for the hell of it.

[rallydad]

Well she ran hard and crisp at the khanacross. A puff of smoke at high revs disappeared after a couple of runs, my guess is maybe a stuck ring. (the motor has been sitting for some time) other than that very happy with it.

 

Heat buildup no longer an issue

 

Ended up with a rubbish result as the course was very soft and slippery. Rules only allowed for road tyres and with an open diff (soon to be rectified!) it made things quite challenging but I had a ball anyway and threw plenty of mud around!. :lol:

 

Now on to the diff....

[B.L.Z.BUB]

http://www.ebay.com.au/itm/Mk1-MR2-AW11-4AGE-Distributor-Heat-Shield-Polished-SS-/370836039271?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item56578ce667&_uhb=1