Too Lean Above 5800 [Fully Rebuilt 1.9 8V]

[Matteo 17 1 Cars]

Hi, I have recently started my fully rebuilt 1.9 8V engine running with std Jetronic management .

The engine has forged pistons and con rods, 280° camshaft with 102,5 peck lift, lightened flywheel, ported head with bigger inlet valves (+ 0,6mm), compression ratio 11,3.

Now I run with fuel pressure at 3,8 bar and std. injectors.

I cannot rev more than 5800 rpm as the lambda drops to full lean side with a modified ECU with no cut off, no rev limiter and wider injector pulse time.

Using my std. ECU the problem rose at just 5000 rpm

 

Have you any suggestion to solve this issue bearing in mind I cannot use a different engine management?

Maybe higher flow injector?

I tested the WOT in the throttle switch and it is OK, the lambda is all the way at 13:1 till 5800 where it suddenly drops to 17:1 with no fuel pressure drop ( so I guess the fuel pump flow is still good, isn' t?).

 

Any help much appreciated, thanks

 

[Cameron 16]

Any reason why you can't use different management?

[camgti 56]

Fuel pressure seems too high. Adjust it back closer to 3 bar and it should have a better spread. I remember having a Adj Reg and when it was too high it would not want to rev. Had great response low down but hated revving. Back to 3 bar and it was perfect!

 

Cam

[welshpug 1,661]

You really have no hope of running that on an AFM IMO, it'll be like a barn door in a gale!

 

Your best option is to spend the £500 on a decent ecu, backing the fuel off to the standard 3 bar, I would think those injectors would be ok for a single t/b 8 valver, fit a proper throttle potentiometer from a ZX plus the 8v xu coilpack thermostat housing.

 

This will give the option of throttle bodies later on with just a map adjustment +maybe injectors.

 

Or spend the same or more on a set of carbs (YUK...)

[Tom Fenton 1,542]

I am guessing Italian regs on modifying mean you cannot run an aftermarket ECU. However there is nothing to stop you doing so and hiding it. The air flow meter can stay in place and remove its guts. Fit a map sensor inside it and use the original wiring back to the ECU. Fit a proper TPS instead of the switch again using standard wiring back to the ECU. If you are feeling really sneaky you could fit an aftermarket ECU inside the case of the original.

[Matteo 17 1 Cars]

Yes Tom, the problem is Italian regs about car/engine modify.

You are not allowed to swap engine type, nor to change any parts of the engine ( of course pistons, con rods, camshaft are hidden ). As you can see my engine looks pretty standard at a glance.

I would try to reduce the fuel pressure to 3 bar, although it seems a little a no sense to me...

 

Too bad I have this issue at 5800, but till this point the engine pulls strong with, of course, a bad idle and no power below 1500 rpm.

 

Is it possible there is no way to modify the Jetronic ECU in order to keep the injectors open for a longer time at high revs? Maybe an electronic specialist would solve this.

[welshpug 1,661]

I would do as tom mentioned, get a Mappable ecu installed inside a Jetronic case, similar has been done by Martin Fox (MEF motorsport) for the 106 Rallye as a plug+play mappable ecu solution rather than having to buy a new loom.

[Matteo 17 1 Cars]

In the past days I have done some different tests and, also thanks to the help from DamirGTI, possibly solved the issue.

Now I can rev up to about 7200 rpm with a fairly constant lambda of 13,5/14:1 all the way from 2000 rpm.

 

My final setup is: bigger Bosch 0 280 150 701 injectors + fuel pressure 4 bar + reworked OE ECU with longer injector pulse time and no cut-off + tightened AFM spring of 11 notches to lean at low and mid revs.

 

Overall drivability is surprisingly good, with only minor hesitations below 2000 rpm at constant opening throttle

[DamirGTI 342]

Nice one .. it starting to settle where it should be ... just drive along with the WB meter connected and monitor the readings , and keep on tightening the AFM but one tooth at a time (when you reach "the soft spot" on the AFM adjustment , one or two tooth’s off of that range will make quite a bit of difference on the lambda value , you'll see ..)

 

Aim to get the lambda towards 12.5/12.9 at WOT ... if you can get it there - that'll be job done .

 

For low down hesitation , you'll need to do something with the ignition timing (advance it a little bit if it doesn’t pink/detonate) ... i haven't asked you which dizzy is currently on the engine ?

 

Damir

[Matteo 17 1 Cars]

About the hesitations at lower revs, I guess they can be considered a feature of this engine running the L- Jetronic rather than an issue to cure. I have a fairly wild cam with a lot of overlap.

At the moment I use a standard 0 237 009 066 dizzy, not the reworked by H&H one which causes the rev-meter to swing , as you know.

[DamirGTI 342]

Yes , it can't be expected for engine in such state of tune to have smooth running on low throttle openings ..

 

Anyway , this one now will need as well an modified dizzy ... it'll run better and unleash more power for sure . So , try to send it back to H&H with new list of engine mods and specify that you want just recurving without overhaul of the whole dizzy (recurving is around 20,00/25,00 quid with VAT and postage included ..)

 

Alternatively , might try with an 1.6 dizzy for a test if you have one .. tough mappable ignition would be the best option and it doesn't cost so much for ignition only

 

Damir