Alan G

Hi all,

I had my Cosworth YB powered Mk2 Escort up on the rollers yesterday to check fueling. Unfortunately, after the first run up she developed a missfire when under load (approx 3500 RPM).

A bit of background on the engine:

Freshly ran in 2wd YB
Freshly rebuilt T34 with 0.48 compressor housing and -31 actuator
803 Injectors
3 Bar MAP sensor
MSD chip to suit the above setup
New MSD leads
New plugs
New GPA coil (MSD)
New crank position sensor

When cold - it boosted well up through the rev range... however, when hot, it started to break down and missfire. I changed out the ignition amplifier and air temp sensor today as I had spares in the garage and they made no difference.

Any ideas what it might be??

Sierrasideways

iTrader: (1)

I've had problems with dodgy plugs before, even when new. Easy to try first I guess...

Mightn't help exactly but I had to check loads of things when mine wouldn't start. You might find something useful in it. Turned out to be a bad coil.

Good luck with it Alan.

https://passionford.com/forum/techni...lp-please.html

Alan G

<p><a href="https://vimeo.com/156169081">Cosworth Powered Mk2 Escort Misfire</a></p>
Click above link to see a video of the misfire.

Thanks lads

cossie2

which plugs did you use...i had same issue like this one when i used denso ik..for some reason it likes 071c..

Alan G

It had 071's in it when we first started on the dyno. It started to break down and then we changed to NGK BCR8ES to rule out the plugs. Same problem persisted.

Alan G

We tried another coil to rule that out... no change!

cossie2

what gap was on the plugs....did you tried to close it..when i was on group a coil i had to keep gap at 0.5 in order to run 1.5 bar of boost

cossie2

are you using 2wd oe fuel press reg?

Alan G

I'm using a Sytec adjustable fuel pressure regulator... set to 3.5 bar at idle with the vacuum off (and blocked) and around 3 bar when vacuum connected as per MSD instructions.

Gap of plugs are as they come out of the box.

Could it be the ECT sensor (blue sensor at the back of the head)??

stevenr

I'd check the gap on the plugs if they're as they came out of the box.

Alan G

Before changing to the NGK's, I had the 071's gapped to 0.6mm and the same misfire developed when she heated up??

Alan G

I did a bit of diagnostics on the water temp sender by checking the resistance of the sensor at different temperatures...

7 °C = 6480
50 °C = 550
70 °C = 360

Seems to be a bit off from the readings in the table below?



Have a set of sensors on the way from MSD so I'll change them out and revert back.

Loomer

What is the AFR when, or just before it misses? and how much boost is it running?

The breakpoints in most 803s maps will reference the top line at around 18-19psi, so at 18-19 psi it will have enough fuel to suit the max boost it will run (around 26psi).
They will go extremely rich until the boost is increased enough to lean the mixture out once you go past 18psi.
Your miss would be around peak torque/boost on a T34.48, so it would make sense.

Loomer

doesn't explain it being ok when cold though, should be worse when referencing big figures from the cold start tables

ram

iTrader: (4)

I have exactly the same issue with mine once engines fully warmed! changed everything you have listed also.
my missfire is at around 4.5k.

Only thing left to change is the blue sensor as i fitted an unkown used one when i rebuilt the engine. I have a brand new msd one sat here but its a pig to get at and its cold outside in the garage

Will be interested to see if this solves yours.

i disconnected my amal valve so it just ran like 9psi and it didnt missfire at all, all the way to rev limit. however engine temps will remain alot lower at that sort of boost so still hasn't really shone light on the issue.

Good luck anyway mate.

Loomer

The engine temp should still get up to stat temp what ever boost your run, and they normally come out of cold start enrichment at around 75degrees, which is below stat temp.

costina

iTrader: (1)

I would be looking at fuel pressure if you have not already checked.

Also what type of fuel system you running? Is the fuel getting hot?

costina

iTrader: (1)

Its a nasty miss just viewed the video.

Is the ignition amp getting hot? Has it the heatshink paste on it?

Can u post pics of the bay up it might help the eagle eyed

Alan G

I've the fuel pressure set to 3.5 bar at idle with vacuum off and 3 bar with vacuum on as per MSD instructions for the chip.

I have a GRP4 alloy tank with built in swirl pot (injection) being pumped up to the rail by a bosch 044. I've got a sytec fse adjustable fuel regulator.

Alan G

I'll grab a few photos tomorrow so you can have a look. I replaced the ignition amp with a spare I had and had the same problem. Neither had the heat sink paste on it? Would this cause a misfire?

Loomer

What's the afr just before it misfires? That will give you an indication if it's fuel related or not

Alan G

Not sure being honest as I don't have an AFR gauge in the car.

Loomer

The dyno it's on must have used one surely?

costina

iTrader: (1)

As james said the above would rule out fuel. And with that set up ot should be fine.
Did'nt the rr operator give you any advice?
Any idea what boost it was running?

costina

iTrader: (1)

James looking at the vid why would the operator keep making in misfire???
Also its very harsh miss imo

Loomer

It's hard to say why he must have been trying to fix it or find issues I'd guess.

The thing is unless you know if it's fuel or electrical you can try chasing faults forever. An afr plot is the first key, carefully watch the afr just before it misfires as this Can tell you if it's heading rich or lean into misfire teratory.
The aft during the miss will be irratic, but just before will give you a good indication of where it's at.

As example if it's running 24psi and the afr is flat 12:1 it's not going to miss there because of a fuel related issue. So you could start looking at ign, ecu sensors, loom, sensor gaps etc but until you have some data your pissing in the wind

costina

iTrader: (1)

Oh yes hell we both know that feeling.
just hope we can help.

Ignition amp getting hot and breaking down? No paste to conduct heat away?
Btw i am facing out of the wind atm

Loomer

it is possible the amp could overheat I wouldn't have expected an rpm related miss there though really

Alan G

Thanks for all the replies so far lads. Some great info being brought to the table. Unfortunately, I don't have an AFR plot, however I was advised to check electrical components / sensors as he was happy with the fueling when boosting etc. We also checked voltage to the pump and it was spot on.

To rule out the chip and ECU we swapped out the ECUs with another L6 (both are running the same spec chip from MSD) and the same problem was seen with both!

Loomer

Is it on a std crank pulley? I've seen aftermarket ones give weird crank signal issues, and have to run an extremely small gap

costina

iTrader: (1)

I know that the escort with a yb in it is a tight squeeze as i built one for a mate.

Sometimes ht leads can interfere with sensors such as map and cps and phase just make sure your coil lead is away from the plugs and map.

Cheçk all 4 points on your crank pulley too.

Alan G

Yeah standard crank pulley gapped at 0.6mm

costina

iTrader: (1)

Beat me to it lol.

Oh btw James coilpack all done cheers

Alan G

Photos the engine bay as requested... tight squeezw is right. The coil and MAP are both mounted on the NSF inner wing but the king lead going to the coil is routed to avoid the MAP sensor and wiring!

tony66

iTrader: (7)

engine earthed ok?
alternator charging fine-not overcharging?
all engine connectors fine...correctly wired? particularly the coolant temp sensor,phase sensor/cap/arm/connectors fine-water hoses beside phase sensor not spraying a fine jet of water onto cap?[happened to me once with a 2wd cossie-fine jet of coolant out of the hose]
ht leads good-all..
map sensor mounted well/working well,hoses/integrity fine? wiring correctly shielded?
timing not moving around[mechanical]-ie keyways etc
tps working fine-wired correctly to suit the ecu?
as said above you need to watch/check afrs and fuel pressure as it comes onto boost

good luck!-keep us posted

Stu @ M Developments

iTrader: (12)

That missfire sounds more like a signal sync problem than ignition related as its global, IE: all 4 pots are missing together which is normally something like crank and phase signal strength problems or their syncronisation.

have you double checked the phase sensor alignment INSIDE the distributor as opposed to that pointless mark on the aux pulley housing?

Alan G

Hi Stu,

I had a look at the phase sensor yesterday inside the distributor. Both red and blue wires seemed in good condition with no splits etc.
I checked the gap and it was in around 0.2mm.

I got the CPS from yourselves a few months ago so I suspect is working correctly. Is there any way of testing these sensors to see if they are working correctly?

Stu @ M Developments

iTrader: (12)

Hi Alan,
Its the phase alignment that will cause this kind of sync error mate. Not gap. The L6 will allow only about 5 degrees of error before it all goes pear shaped and the alignment mark on the front of the casing should be ignored.

Has it been aligned properly?

Alan G

Would I be correct in saying that to align the phase sensor I should put the crank at No 1 TDC. Check that the rotor arm points to the scribe mark on the upper face of the distributor? I will confirm this later!

With this in mind, I did notice that there was quite a bit of play in the rotor arm. Approx 15 degrees!!!!

I have a new rotor and cap coming from you guys (ordered from Steve) this week so would definitely be worth a try! Would this explain why it is only happening when hot though??

Loomer

Its the temp part of your problem that threw me off sync error etc. I guess i could somehow be possible though.