Lovemyevo2

My mechanic and I are at running out of options now to solve a persistent misfire that has meant my car's been in the garage now for over 2 months! I will try to explain all the work that's been done to-date in the hope that someone might suggest another stone we might turn...
The misfire seemed to start shortly after I replaced the fuel pump with a replacement but used item - at this time the fuel system was flushed and I believe the fuel filter changed. This might be coincidence? It started quite mild but has gotten much worse over time. The car seems to run fine when it's cold but as it warms up the misfire gets worse. The misfire is most apparent when the car is accelerating - it just chugs horribly then when it hits a certain RPM it seems to accelerate up. Although now it's got worse it finds it quite hard to even raise the revs sufficiently to get through the chugging to higher RPMs.
It looks like the engine is running lean due to white plugs (all) and when the emissions are tested when it's 'chugging'
So, we started with ignition and replaced the twin dizzy bits and fitted new coils. Ignition leads look in good shape and seem to measure the right resistance. Alternator was reconditioned less than 12-months ago.
Then onto the air system. MAF sensor was sent away to be calibrated. Throttle body cleaned up. Rubber connection between the throttle and the plenum replaced as was very perished.
Then onto fuel system. Previously fitted 'used' fuel pump replaced with a new one - correct pressure found on the fuel rails even when it's 'chugging'. Two new fuel regulators fitted just before I bought it by PO. Injectors all removed then sent off to specialist be tested, and refurbished. All returned working 'perfectly' All injector pipes replaced and fuel rails cleaned.
Electronics. All grounds checked and cleaned. Both the ignition and the injection ECUs removed, sent away for testing. Both returned operational having been tested on another car. Continuity tested in the loom around the injectors and ECU. Temperature sensor tested and seems to be operational (we are planning to replace this part next just in case)
Vacuum. Seems to be fine - throughout. This is the next major area to test by process of elimination. Although my mechanic doesn't believe that a tiny leak would cause such a major misfire unless it was affecting the ignition.
I think this covers all the areas we have explored to date - it's sooooo frustrating. Any help anyone could offer as to what might cause this terrible misfire when the engine warms up would be massively appreciated.
Thank you in advance
Tim

AO

How does it idle?

Can you pinpoint it to a specific cylinder/cylinders? RPM range?

If it's a misfire, that usually indicates a specific cylinder, but it sounds like it's struggling to fire under load? Is that correct? What happens if you immediately mash the accelerator? Does it run any better?

The one thing that immediately jumps to mind is the throttle position switch or the LH. If you have a friend with a spare LH, you might try that first. Alternatively, you might try contacting John Speake to see if he could hook up the SHarkTuner to your car to quickly diagnose a number of items (but I have no idea where you are located in relation to him).

The final stage ignition "things" at the nose could impact things, but rarely go and tend to be an all or nothing affair.

If it's across the board, then it must be something universal like MAF, fuel delivery, computer, etc. I doubt it would be vacuum related. And just because something was replace before you got, does not mean it can't be bad.

Jetdriver69

I had a bit of a misfire on my 82 5 speed with 85K original miles that I recently bought as a project for my son.

I thought it was the ignition as the wires were old. I replaced ALL the ignition components which needed done, but it did not help. My engine sounded like a lopey cam small block chevy at idle. I tried advancing the timing, but that didn't help either.

I did a compression check and a leak down check, both showed #8 cylinder at very low compressions and a 35% leak down. All other cylinders were 155-160 compression and very little leak down.

So reluctantly, I pulled the engine in order to pull the heads. What the heck, may as well replace all the seals, gaskets, etc. while I was at it.

Well it seems some time in the not too distant past, one of the pistons rings had broke and beat up the top of the piston along with the head section. Funny thing, the PO didn't mention anything about this problem, LOL!

Someone had pulled the head, cleaned up the damage without repairing anything and put it back together. The car didn't actually run too bad with a dead cylinder and smoothed out nicely at higher RPMs.

So I redid the heads, re Alusiled the block, new piston, new rings, all new bearings, gaskets, seals, etc. Parts costs was about $1500 and machine work about $1000.

I'm not saying this is your problem, but a compression/leak down check won't hurt anything. Good luck and I hope your PO had more integrity than mine had. Nothing like taking advantage of a 16 year old looking to buy his first car. There is special place in used car hell for people like that.

GlenL

Right... Something new or rebuilt could be bad right away.

It does sound like electrics. I'd clean grounds and replace relays. Then look at grounds and supply voltages while it's running.

Check the temp sensor resistance at the ECU.

Does it miss when hot and not under load? That is, when it's being revved in the garage?

Am I missing O2 sensor replacement in the list?

John Speake

Contaminated fuel ? LH and EZ-F were fine when I tested them in my car..... MAF calibration was reset.

I've discussed your car at length on several occasions with Blaize and it defies logical analysis !

Glen - all these Euro 16v 84-86 were without cats/o2 loop.

John Speake

One thought - get Blaize to check the vacuum at the EZ-F varys with engine load as it should.....

AO

Yes... this is a good point but i;m not sure a missing or loose vacuum line here would do much. A simple vacuum gauge (pick them up for ~$30 here) would help verify this.

The EZF has a vacuum sensor that adjusts the timing of the spark. But I'm not sure the dynamic range of the ignition table would be enough to cause the cited problems.

Lizard928

Is the misfire at idle, or only under load?
Dual distributor?
What spark plugs?
What ignition leads?
Have you swapped the final stages?
The 8 rubber seals from the runners to the center plenum, new?
Has the base CO been set as per the manual?

Lovemyevo2

Thank you all very much for your fast feedback. See below for responses to all suggestions:

AO:
No, we can't pinpoint to specific cylinder or RPM range
Yes, sounds like it's struggling to fire under load. No, mashing the accelerator doesn't help. However,
JDS has actually checked the MAF and the ECUs for us and confirmed these are okay.
It seems it does actually rev fine when not under load. While it is 'chugging' if you keep it floored while it is stumbling and then slip the shifter into neutral, it takes about a full second to 'clear its throat' and then revs as normal.
Not sure my car has a final stage ignition amplifier but if it does it seems they either work or don't?
The only thing that was replaced before I got it was the fuel pressure regulators but the pressure on the rails is good even when it's 'chugging' suggesting these are working fine.

Jetdriver69
You're making me shudder with that story...I'm sorry to hear but what a great car for a 16 year old. My Dad bought me an Austin Maestro LOL!
We've checked the compression in all cylinders and it checks out fine as around 160 across all 8

GlenL
Grounds have been cleaned and the essential relays replaced
Both sensor readings have been checked at sensor and at ECUs and they both check out
Yes it does miss when hot and under load. Although at idle it cools down enough to make it harder to perform badly at a standstill

John Speake
Not sure how the fuel might be contaminated as it's run fine for a year or so under my ownership but we could drain down and replace?
I know you've been very helpful to us - thank you!
We're checking the EZF vacuum today / tomorrow

Lizard928
The misfire can be heard at idle but it just manifests much worse under load
Yes, dual dizzy
The plugs are standard fit for this model - we think they were BOSCH
I have aftermarket custom leads from perfomanceleads.co.uk
All plenum seals have been removed and very closley inspected, all look to be in near new condition, all hose clamps are clean new and tight.
1.5. As per John at JDS we have been setting the idle CO to 1.5 and the Lambda ends up around 1.1 at that setting.

Thank you all again - any further suggestions with the above info would be muchos appreciated.
Cheers
Tim

AO

Hi Tim... When it "clears its throat" is there any smoke coming out the tail pipe? If so what color? Blue, Black, or White?

Also, How's the coolant level? Any coolant loss? Any unusual smoking on startup?

What gets me confused is this seems to be worse when it gets hot.

And yes... your car has the final stage ignition modules. They are located under the black cover pictured here at the very front of the engine to the right of the hood latch.

ROG100

Run the car in the dark and spritz water above the engine while running and look for fireflies/sparks. Aftermarket wires give me goose bumps.

Used fuel pump raises an alarm as well. Is it a UK delivered car? No internal pump.

Check the wiring where it bends just before the MAF connector for shorts.

Check the wiring where the CPS harness connects to the engine harness, Has the CPS been changed? If not change it.

Brett928S2

Hi Tim

I am in Bournemouth (less than 20 miles from you)... is it driveable enough to get to me ???

I used to be a Race mechanic so should be able to figure out or cure your problem...if yours is an S2 the same as mine we can swap bits off mine as well....for free of course

My first thoughts are an obvious electrical missfire... when were the plugs and leads last CHANGED ....NOT looked at or tested but actually CHANGED ????

My shop number in Bournemouth is 01202 - 525952 or my mobile is 07976034331 ... I will be more than happy to have a look for you if it helps ?

I have a lot of Snap-On tools.... gas analyser etc etc...

All the best Brett

Lovemyevo2

Okay next round of answers - thank you for your continued help!

AO. No evident smoke on startup or when it 'clears its throat'
Coolant level seems to be fine. Just as a FYI, I fitted a new radiator when I bought it as there was oil / coolant mixing. Total flush of block and it ran fine for months after this until this new problem arrived.
Thank you for pointing out the ignition modules - I'll replace these as a precaution
BTW - lovely looking engine!

Rog100
We've spritzed the wires in the dark and no illuminations. However, they're probably not up to the temperature (and therefore the resistance they get to) to cause the problems as they are when hot and driving. This is a major area to explore as they might start shorting when they get hot. I'll see if I can replace these.
Fuel pump is new
Checked the wiring where you recommend - all seems to be good
CPS is new

Brett928S2
Whooppeee, someone who owns one of these near to me. I'll call you shortly. Thank you for getting in touch.

Thanks again all
Tim