Big flatspot on Bluetop 4AGE- but I think I might have an idea

[Lauren]

Right, I've bought a car with an early bluetop 4AGE.

It's an AE86 Sprinter Trueno GT Apex (same model and colour as Initial D). There's a big thread in off topic about it.

When I test drove it, it had a horrible flat spot at 3K which was really annoying as it's hard to avoid. Also the engine felt a bit sluggigh (but I do admit to testing a blacktop 20v Levin earlier which was stonking, shame about the rest of the car) through the rev range, though I wonder if being put off by the digital dash was a factor as it didn't seem that bad at higher rpms.

So when I go to pick the car up next week, I'm going to change the ignition components. I noticed tha the engine was missing the spark plug cover and had later leads on it which are not the same as bluetop ones. Also the guy admitted to not servicing it, since it landed in November 2010.

I've bought (all from Toyota):
Dizzy cap
Rotor arm
OEM Spec platinum plugs
HT Leads

I'm thinking it's missing a bit all the way through the range. Am not absolutely convinced that changing these items will sort it. It might need a bit of a throttle body clean.

Obviously will check the timing too, but I'd reckon that a timing issue wouldn't cause a flat spot.

Any other thoughts on what it could be. Only other thinking was a shagged TPS or it's well rich.

[PW@Woodsport]

Back to basics to sort the issue methodically Lauren.

If you feel it's not quite right through the whole rev range i'd definately be checking the cam belt timing first, the 4age is a bu88er for people mistiming the exhaust cam by one tooth, it springs while they fit the belt and 9 times out of 10 goes unnoticed.... people then try to "dial out" the rough running with ignition advance (driven off the exhaust cam so ends up being out anyway!)

Might not be this but it would be my first port of call

[Lauren]

We will check the timing, though we'll have to wait till we get home. Ta for that.

[PW@Woodsport]

No probs, a compression test would be next , extreme i know but like i said make sure the basics are right then work your way down.

Out of interest, jumping the gun a bit, but are there any error codes?

[Lauren]

Haven't had a chance to check yet Paul, don't get the car till next Thursday and didn't check for error codes whilst we were there.

I'll change all the ignition components when we go to pick it up, as that is easy to do.

[PW@Woodsport]

Ah i see, well it'll be easily sorted i'm sure, anything specific you need just ask.

[Lauren]

Cheers Paul.

[MartG]

General sluggishness could be as simple as a blocked air filter

[PW@Woodsport]

It could well be.

[Lauren]

General sluggishness could be as simple as a blocked air filter

It did feel really asthmatic tbh. Will be sticking a K&N on when I pick it up.

Guess it's a bit of a daft thread as I haven't got the thing yet, but was just wondering what else people thought could be an issue. Forearmed and all that.

[Lauren]

Okay got the car now, yay!

Put all the new ignition components on and still got the flatspot.

However when we took the cam cover off to check the belt we found this:



Thinking it's pretty likely it's got HKS cams. Also noticed yellow painted marks around the head to line up the cam wheels.

Once I saw this, I put it all back together again, with the addition of a K&N and some bits and pieces including next door neighbours drain pipe (that fell into our garden) and off we went. Noticed that once you clear the flatspot 2.7-3.4K or so, it picks up well from 5K or so, it seems to rev off the end of the rev counter, which goes up to 8K (digi-dash).

Also noticed the manifold is a 4-1 so it's setup for top end power by the looks of it.

I figured, probably not best to rev beyond what I can read, but it really does pull strongly at the top end.

So, given this, I'm going to leave it as is, until I can get it on the rollers and maybe look at a unichop or whatever it is now.

Sorry it's the wrong way round.

[Lauren]

More news in, (thank you James), the cams look to be retarded which apparently gives a little bit more at the top end (ie more revs) at the expense of messing up the bottom end.

I might put the cams back to stock as after all it's easier with verniers and see how that goes.

[JMR_AW11]

Hi Lauren
You finally bought one then...

I'd love to have a drive in one but not sure I'd want to pay the £££ to own one.

Is the 4 to 1 exhaust standard? I know virtually nothing about these cars.

If it isn't then maybe the 4 to 1 is causing the flat spot as it might be adversely affecting the VE vs MAP sensor reading at the affected rpm although I'd be surprised if it could make it as flat as you describe.

[toxo]

According to my parts catalogue the stock manifold is 4-2 with the 2-1 bit being done in the downpipe. It also doesn't look anything like the one in the pictures I presume from that that a 4-1 manifold requires a completely aftermarket exhaust.

Also noted that the stock manifold has the O2 sensor at the bottom of the manifold where it's still in 2 parts. Where's yours on the aftermarket one?

[Lauren]

4-1 manifold is most definitely not standard, it's not cast iron for a start(!).

Oxy sensor is in top of manifold on one of the down pipes.

Cam timing I think is the most likely cause, so probably going to set it back to stock and see what it's like. Retarded cams would explain the bottom end of the rev range feeling weak. Is pretty strong at the top end though.

Also has a cat back system (tanabe medallion) which doesn't sound too bad really, is a little bit boomy on the motorway but is still in fair condition so will leave it for the mo'.

[jon_st205]

The cam retard might just mean a bit too much fuel is going in at that point especially if enough vacuum being created to open tvis early - needs a cpl of wideband runs to check. It would be shame to mess with the cams and ruin the top end.

Jon

[Lauren]

Yeah quite. Have set it back to stock and it is still missing at those revs it was before, but will try a drive around the block once the alarm guy has done his stuff.

I can always put it back to where it was. Was 6 degrees retarded on the verniers.

ECU looks stock.

[Lauren]

Decided not to drive round the block as it was clearly no better so put it back to where it was!

More research required I think and when I get the cam cover gasket I can lift the cam covers and see what I have.

[LimeyMk1]

May be a good idea to see what the compression's like as it may have had the CR increased.

IIRC my old 4AGE with a TRD head gasket was up in the mid 190's (psi).

[Lauren]

Hmm, fair point Chris. I guess this is always the fun with lightly modded imports, finding out what has been done etc. Some nice surprises so far, but makes it all a bit more complex to sort out.

Think I want to get the cam covers off (once I have some gaskets so I can refit them) and see what I've got. ECU looks stock to me, so wouldn't expect cams more than 264s really.