Injectors not firing [MX5 MK1]

Technical Area Engine, Transmission, Exhaust etc
1
  1. My model of MX-5 is: 1990 Eunos 1.6 B6
  2. I’m based near: Hull
  3. I’m looking for technical help or recommendations on: Injectors, Relays, Wiring, Engine Management, Fuses, Fuel Pump etc etc

Hi all,

Bit stumped on this one! Hopefully one of you MX5 wizards can help me diagnose/fix this one - buckle in!

Current state/configuration

Engine: B6 1600cc
Induction: Forced/Turbocharger
ECU: ME221
Supporting Engine Accessories: IAT, Boost Control Solenoid, 420cc Genuine RX8 Injectors, Integrated MAP, BWM TPS, AEM Wideband O2 Sensor
Removed Engine Accessories: Air Condition Piping, MAF

The Problem

Preface: The car has been running sweet for over a year with no modifications or adjustments to mechanical or electrical configurations since.

(1) Initially the engine exhibited running issues where, when coming off-throttle, the RPMs would remain high (3000-4000 RPM) and take an eternity to settle.

(2) Next, the car developed an intermitted fault where the engine would cut completely and it would be unable to start for 15-30 minutes. This happened 3 times, twice at idle (~1000rpms) and a single time on the motorway (~3500rpms).

(3) Since the last engine cut the car has been unable to start since. The car cranks but makes no attempt to start.

What I’ve Tried To Check

(1) Checked spark plugs: when cranking, plugs observed to create a strong spark
(2) Checked fuel pump/pressure: when ignition live, fuel primes and has been observed to drain out of the fuel rail at the fuel pressure regulator
(3) ECU Software: TPS position, Injector Duty/PWM, Crank Position & all other relevant data seem nominal
(4) Fuel Relay & Fuse: Fuel pump stops and starts when relay/fuse removed, continuity to Relay from Injectors is found to be OK
(5) ECU Electrical: ECU is grounded and communicating with laptop/software
(6) Injectors Electrical: Injectors have 12v live supply when ignition on, the ground to the ECU has also been checked for continuity and this is OK

Other checks:

(7) Fuel sprayed directly into intake manifold on crank and engine will begin to run
(8) Old stock injectors reconnected to injector plugs, tried to listen to them, don’t appear to be firing
(9) Spark plugs are dry after continuous cranking

Summary of the Diagnostic/Issue

Injectors not fuelling engine

Cause of Issue

Unknown

Planned Diagnostics

I have been informed that the injectors may read 12v and have a ground connection under “no load” conditions but may still fault when in use. I have ordered a Noid Light Kit so that I can check whether the injectors are receiving a signal under load conditions. I will update this post with the results of the Noid Light test when I get the kit.

Other than this I’m a bit stumped.

Let me know if I’m missing anything obvious.

Thanks in advance,

Sean

2

Crank angle sensor? You’ve made no mention of any tests with regards this?

3

The best plan of action would probably be to make a datalog of it failing to start and then go talk to someone like Alex Hickson and see if he’ll have a look at it for you, hopefully he’ll be able to spot why it’s happening. he’s also a complete wizard, his helps been tremendous on my turbo build

It’s Alex I’ve got dealing with my map remotely and there hasn’t been a problem so far he hasn’t been able to sort out, he sorted out my map for n/a to get it running and I’m now waiting on an adjusted file with boost for my first start

4

I think the crank angle sensor is okay as the timing on the ECU side seems nominal ~14 degrees. Also the car will produce a spark at the correct time and run on fuel supplied separately through the intake using a spray bottle.

5

I created a data log yesterday. From what I can see the ECU “thinks” its doing the right thing. Sending the correct signals at the correct times. The car has been running on a professionally tuned map since last year with no problems which leads me to think its some electrical gremlin like a bad ground or a poor supply that I just haven’t manged to trace yet.