Running Lean in boost

Hi guys,

I've suddenly started to run really lean in boost.

I get to about 5psi then car misfires/stutters, reading about 1.3lambda on wideband when this happens...

Car is tuned for 20psi.

Car idles fine and cruises around fine (when not on boost)

Using Microtech mt-8 - old ECU but does the job (most of the time anyway)...

It's open loop.

I've swapped out fuel pumps/strainers, fuel filter is new, all fuel hose is new, FPR800 is new.

Drained old e85 and put new e85 in, although there's probably only a 1/4 tank left in it...

I've changed intercooler clamps for new ones and made sure they're tight.

Fuel pressure is 3 bar at idle.

I checked to see if Turbo was spinning, and it moves freely, can also hear it whilst driving.

I've done compression test and each cylinder is around 165/170 which is normal.

Spark plug 3 was wet, but not sure if this would cause the problem.

I did have a problem the other day where I was running lean at idle with accessories on, but fixed that with adjusting fuel map (20hg-30hg cells). (had another thread on here)

Any help would be appreciated thanks :)

That sounds a lot like a misfire on one cylinder. Have you got new plugs in it? Any evidence of different corona on the wet plug compared to others? Any tracking on lead or coil?

Could be a coil breaking down internally as chamber resistance rises too. If you put in new plugs and can swap in a coil on the cylinder that was wet that should rule out a likely cause.

Hi Slides, they're pretty much new plugs. Less than 1500km.

There isn't a corona on base of plugs.

The ignition coil is new. The ignition leads are new as well, except for the one that runs from coil to distributor... New lead doesn't fit well on new ignition coil so used the "old" one.

A high lambda with a mis-fire is very strongly suggestive of an electrical issue with the 'plug not firing, as Michael said.

Being 'wet' wouldn't be the problem, per se, but it will be a symptom of the problem.

Have you tried swapping around leads, or at least checking the resistances of them - one could be faulty as made - also have a good visual check for cuts or wear marks. Have you checked the condition of the dissy cap and rotor as, while uncommon, it is possible to have one that fits but the internal terminals in the wrong place, or have the rotor mis-aligned on it's drive, or it may be a physical fit but the wrong tip design.Old=school check was to take an old cap and carefully cut around the #1 terminal to expose it, then use a timing light to check the alignment of the tip to the rotor at different rpm and loads - this can be a particular issue as the old type vacuum advance would change the relationship between the points opening and cap position.

The spark plug may have had the porcelain cracked in fitting, or during transport - try a fresh 'plug and gap them 5-10 thou less than OEM and see if that helps

The problem ended up being a clogged fuel filter... the filter is pretty much brand new... must be rust in tank that the e85 has cleaned up. 🤦‍♂️