S14 RB25DET - misfire and destroying fuel

[handsomedez]

I've only had my car on the road for a couple of months now since building it and having some trouble getting the engine to run properly. It's basically a standard RB25DET, standard turbo, ECU, injectors etc, but with uprated head gasket, oil pump etc. Just trying to get it to run reliably before I go for big power.

Engine seems to idle pretty well but when driving there's always a hesitation when opening the throttle. It backs off as if it's run out of fuel then goes again, but there's always a mis-fire when the engine is under load, and it seems to run out of puff about 5k rpm.

So far I've checked and gapped the plugs (these were new last year, NGK decent plugs which have done about 200 miles max), adjusted the TPS so it reads 0.45v when throttle closed, checked the coilpacks for any obvious signs of the them breaking down etc. Have still to clean the MAF but looks clean and in good condition.

My AEM wideband gauge reads between 14-17 when cruising which seems a bit high - am I right in saying that means it's running lean? The car destroys fuel at a horrendous rate. I'm barely driving on boost and it's managing 80-90 miles on 30 litres, which I'm putting down to the misfire. Fuel is 97 RON and any old petrol will have been flushed out by now. I've put about 70 litres in it since it went on the road, which has lasted no more than about 150 miles.

I previously had a 400LPH pump fitted and the fuel pressure was so high that it was chucking petrol into the engine and filling up the sump with petrol, plus the exhaust was sending clouds of petrol smoke into the unit - was really stinking. Have had a Walbro 255 fitted for about a year now and seems to run fine if a bit rich smelling. Also worth mentioning before I built the car I "refurbished" the injectors with new seals, nozzle caps etc before I got the engine running. Could I have ruining some or all of the injectors? Does seem like a stupid idea now! Running standard RB25 injectors, fuel rail with built in FPR etc.

Think the engine is pretty much boost-leak free, although haven't gotten round to doing a smoke test yet. Any other ideas?

[p.nicholas]

sounds boost related to me. Checked for boost leak?

[handsomedez]

sounds boost related to me. Checked for boost leak?

That's my next port of call, need to do a smoke test. You know how it is, you're always sure you've tightened all clamps and fixed all leaks but in actual fact it's leaking like a sieve. There is a high pitched whistle when it's idling which I'm sure is a small leak.

[ANDY black s13]

agree with paul reads as a boost leak, another could be an air leak after the MAF on the intake pipe to turbo entry
could check compressor housing bolts are tight as well

[handsomedez]

agree with paul reads as a boost leak, another could be an air leak after the MAF on the intake pipe to turbo entry
could check compressor housing bolts are tight as well

Good shout. Will check those connections today although I put new jubilee clips on the air intake just a few weeks ago. Got a friend to do a smoke test on it yesterday and I'd missed the nipple on the underside of the throttle body, so was leaking there and the hose onto the FPR was a bit loose too so replaced that. Pretty sure there's no boost leaks now. Car is driving a bit better but there's still a hesitation and doesn't feel like there's much power until the revs are up about 4K. Also every time I go over a bump or a pot hole the engine hesitates as if it's running out of fuel, so need to check the pump is seated properly in the tank and make sure the fuel lines are clear.

[autosri]

Coil packs not secure/loose looms or maybe a broken spark plug ceramic ?

[ANDY black s13]

have you checked ignition timing with an old spark plug lead between the plug and coil pack for signal
the coil pack loom harness loop gives a slight signal delay so won't be bang on
15 degree btdc at 650 rpms on stock engine,may need unplug tps switch and the knock sensors if engine is rough on idle
it may detect knock and back off timing as it's being adjusted and the timing marks will wander + & - 5 degree

[handsomedez]

Coil packs have been in and out a few times. Even cleaned up the mating surfaces to make sure they're earthing onto the engine. Not sure about the plugs because the engine was started lots of times and left to idle for a couple minutes but never driven anywhere. So they could need replaced. When the engine is cold it starts fine after a couple of turns but it splutters for a few seconds then settles and idles smoothly.

Still to clean the MAF when I get round to buying a can of brake cleaner. Timing was set a few months ago (at a trusted garage who work on these cars regularly) before the car went on the road so that shouldn't be an issue.

[autosri]

Don’t use brake clean on the maf if leaves a residue behind you want a tin of isopropyl alocohol

[handsomedez]

Replaced the plugs at the weekend and cleaned the MAF, and it runs better but still got a misfire, also still feels really down on power like a boost leak.

I had the car up on the ramp tonight and discovered both the cold start air regulator and the AAC valve were unplugged. I plugged in the cold start vale but the socket on the AAC valve is broken so need a replacement, which means front facing inlet manifold off (nightmare). Not convinced that's my issue but certainly can't be helping.

[Zeldoz]

I had no end of random intermittent problems with my conversion that I done myself.

MAF I replaced 3 times as even when I thought the first 2 were okay they wasn’t!
Bad earths, check you have enough offf the engine and they’re clean.
Fuel filter - Mine was bad, replacing helped when on boost I felt.

Then make sure you’ve setup the VAC lines properly and blocked off any not needed.

The above cured a lot of issues with mine!