Lean combustion?

[KenS]

The manual vacuum gave interesting results with not having the periodic change in revs! Does this imply that those sudden change in revs are not caused by a lack of spark or bad injector? Or was it not quite low enough pressure to help initiate the upsets? Do you know if the right angle filter thingy feeding from the manifold to the MAP sensor pipe is OK? Wonder what would happen if it was no longer a filter and allowed transient pressure changes through to the MAP.
But ...
I have expanded one of the manifold pressure/rev pulses from '26 try fuel reg..' to see its time relation with Injector pulse width, IAC position, Air/Fuel ratio.

sml7-10-26.jpg

It shows the injector pulse width is significantly reduced prior to the manifold sudden pressure change. So I think the root cause cannot be directly related to the Manifold pressure but something that has required the ECU to reduce fueling. I guess this does bear some similarity to the original problem, so they may well be related.
ElanScan is giving ECU driving values, not necessarily values that are achieved by the IAC or fuel injectors, so its hard to know for sure what they are doing, maybe a fuel injector is occasionally overfueling causing the ECU to suddenly reduce fuel on all injectors, or maybe the IAC snaps shut occasionally, causing revs to drop, air/fuel ratio goes down causing the IAC to be immediately raise a few counts and fuel reduced. I'll have a deeper look at the O2 sensor voltages during these dips to see if there is any clue to what the injectors may be doing. (I am going away for a few days so I will probably go quite for a few days!). Good luck.

[Chas54]

Ive measured the resistance of the injectors at around 2.6ohms, all very close to this. I have just ordered an injector test light to see if i can spot my dip in revs corresponding to some intermittent flashing.

Also cleaning up every connection around the top wiring loom .

Chas 54

[Tuga2112]

Ive measured the resistance of the injectors at around 2.6ohms, all very close to this. I have just ordered an injector test light to see if i can spot my dip in revs corresponding to some intermittent flashing.

Also cleaning up every connection around the top wiring loom .

Chas 54

you can just use the timing gun light, and put the loop around each of the wires. mind you. that will tell you the power is there, but wont tell you if the injectors are opening and closing. that would require a different type of test tool

like this
https://www.ebay.co.uk/itm/317812260496

[Chas54]

Tuga

Im not convinced the timing light sensor will pick up the small amount of inducted current on the injector cable. The voltage of its pulses must be 12v or less?
As my 'noid' lights are taking some time arriving i may test the theory.

I still think i am seeing a missing intermittent spark on no.3 . It does correspond to a dip in revs when idling every 21 seconds . Its a bit weird really . I have swapped the coils round so what was 1/4 is now 2/3 . With the coil construction being it is exactly the same windings and and LV terminals that produce the spark for both 2 and 3 , it would leave the missing spark issue being from the coil HT terminal to the no.3 cylinder.

Ive done a compression test , all the same pressures.
Swapped the plugs about and swapped the HT leads about.

Ill try the spark plug and leads again today and now i have enough leads i should be able to identify one that alway works on other cylinders and use that on no.3.

But i am wondering if it is an injector problem. I can only think it throws to much petrol in every 21 seconds its too much for the plug and thoroughly wets it and shorts out inside the cylinder.
After i finish swapping my plug and leads around again and run the engine to idle and test noids, I think ill have to swap the injector no3 for say no 2. See if i can move the issue to no.2 cylinder .

Thanks for comments though
Chas54

[chrism]

Chas54 I'm having (what I think to be) f/inj issues.

Cyls 1+3 have died and I suspect a 'bad' injector has failed pulling the other circuit down.

In order to get ins breakdown service to relocate to my fave classic car repair man I had to have a breakdown van to pre-assess. He used these to verify a strong healthy spark on all cylinders and I was really impressed



I'd never seen them before...might save you swapping plug leads around and you can see all the sparks 'in real time'

ps I've found that injectors fire as pairs 1+3 then 2+4 and when one breaks it switches off the other in the pair
Ignition uses 'wasted spark. 1+4 then 2+3 fire simultaneously, which made me suspect f/injs rather than coil packs.
Plus, I gather there's a m/plug hidden under/close by the coolant overflow that governs f/inj electrics. It can get corroded with overspill and may need a bit of wrangling to get it going again as can the coil packs in the same area.

Hope any of this can help

[KenS]

I think the injector theory is quite possible (but probably best to rule out the ignition/spark first). Removing each injector plug one at a time may lead somewhere, it may run differently for each of the 4 plug removals and the pattern may imply something. If it comes to it, I have one spare new FJ559 injector from RockAuto that I could send/lend, which may help to confirm any findings, just swapping injectors is not an easy process but gets easier with practice! Good luck.

[chrism]

pps if you take off the plug of the 'suspected bad' fuel inj the other of the pair will start firing again and you'll be back to 3cyls...
So...it's a 50-50 guess using injector pairs 1/3 or 2/4 to find the culprit.

ppps our injectors are low impedance of ~2ohms. They can vary between ~1.8->2.5 but no higher. This'll further isolate a bad player.

pppps try getting new f/injs in UK at this moment in time - they all seem to be 'on order' - and imo be careful not to buy Ultra-power MFI31's despite some assurances that their '1991 ISUZU Impulse 1.6L Turbocharged' flow rate matches ours. (I've verified they have 2ohm impedance tho'...)

ppppps I'll imminently have a used spare that you can try, rather than break into Ken's new part. And it'd be available for you to keep if it cured your problem...just a thought...

[Chas54]

I started today by testing with the strobe and convinced myself the intermittent spark at No3 cylinder was there still.
I swapped the lead and plug for some old ones I had around. Still on number 3.

I then swapped the position at the lower coil so the no.3 lead was now going to no.2 and the no.2 lead was going to no3 cylinder. The missing spark problem moved to no.2 .

So it looks like the problem is with the normally No.3 output on the lower coil. How this can be I have got no idea. I didn’t notice this when I swapped the coils round a week or two ago.
Unless its something to do with the LT connections and ive just made a better fit ?

Ive lost one of the rubber seals from the lower ignition plate plug .

Ive now swapped the lower coil for an old one I had and the missing spark seems to have gone now although the engine was smoother idling at its best periods before on the other coil.

I tried the noid light tester on all 4 injectors in turn . The noid light is not very bright but can be seen flashing evenly on all injectors. Incidentally, I couldn’t get my ignition strobe to detect the injector pulses.

I think it might be time to solder all the wires back onto the ECU plug and O2 sensor and see how it runs..

Kens Thanks for the offer but I do have a spare set of injectors I had cleaned and tested. I havent used them since as I had the fuel rail sat on top of the engine with newsapaper underneath and when the fuel rail was under pressure I noticed one built up a drip. At the time it put me off using them and I bought a new set from US .

I do like the look of the spark plug test inserts an at around £12 a set of four looks a good investment – I have two other cars with magnetos and its always a bit hit and miss to tell if theres a spark sometimes..

The plugs on the ignition module plate are susceptible to any coolant spillage and I have found a bit of a drip from my header tank bottom hose . Its bin off and on so many times in the past few weeks, its getting a bit tires.

Ive attached my two elanscan traces from today

First was whilst I was swapping the leads and testing all the injectors with the dismal noid light. Im wondering if the noid light being so dim is a clue? . I think ill have to test it on a 12v battery and if its brighter I will have to check the voltage at the injectors when running.

If I have proved my issue is coil failure I cant picture what the fault is unless I am completley miss understanding the coils construction.

Thanks again for all advice comments and suggestions.

swapping lead and coil position noid.zip

after lower coil swap.zip

Chas54

[KenS]

Is good that you have found the cause of the regular drop in revs, that last plot after the coil change does look far better in that respect. The plot still shows the O2 sensor voltage as odd, slow to start-up and maybe lean, so reconnecting the wiring around that does make sense, then establish a new baseline plot. You say you have fitted new US fuel injectors - have they worked well prior to this problem of dropping out of closed loop and 'lean' CEL fault codes?

[Chas54]

I bought the US injectors in 2021. I think they have been OK until this problem appeared