New 3.1L Misfire Help!

[Riceburner]

Hey guys, I have had the new 3.1L engine in for a few days and I'm having an issue that's really starting make me pull my hair out. The first time we fired it up it ran rough as the timing was retarded, so set that correctly and cycled the engine to temp a few times. It ran sweet, smooth and with a deep consistent burble.

 

Next day I go to fire it and it's missing from the start. Number 6 lead when removed seems to smooth out the miss. It was only missing every 5-10 seconds. I went through and checked/replaced tappets, new plugs indexed and gapped, dizzy cap replaced, dizzy rotor replaced, fuel pressure is normal at 2.5psi, carbs are synced perfectly, oil is clean no signs of milky colors, radiator doesn't have any oil in it, plugs are starting to show signs of a very light brown on the insulators and no signs of any crusty white coloring. Tested resistance of leads last night, coil-46ohms, 1) 56.9ohms, 2) 56.8ohms, 3) 57.4ohms, 4) 63.4ohms, 5) 66.2ohms, 6) 67.2ohms.

 

 

After doing all this I started it again and found the misfire still present but happening much more often, like every fire. I increased revs and the miss increased also.

 

I pulled the leads off to check plug color and number 6 had broken the metal end off and stayed on the plug. Could this be the issue even though the resistance checked out ok yesterday?

 

Leads are IC&E 9mm helically wound 'Pro 100 Series' which is the top of the range leads. 5years old if my records are correct.

 

Any help is much appreciated!

 

Pic of plugs 5&6 below with the lead end still on it.

Edited January 5, 2016 by Gareth. J.

[d3c0y]

Don't have the dizzy 180 degrees out from when you reassembled the motor?

[Riceburner]

Hi Jake, it's pointing at #1 when I'm at TDC, timing is spot on 15 degrees and ramps up at 2300rpm as per the book. It actually starts really easily, 2 pumps of the pedal, push the button and it fires into life idling at 800rpm.

 

It was out initially as the factory timing plate was actually out by a little over 5 degrees when I had the dial indicator on for the dummy build.

Edited January 5, 2016 by Gareth. J.

[EJ101]

so its not running lean?

 

does it miss throughout the rev range or just at idle/low rpm?

 

vacuum leak?

 

i had something like this years ago and it was the coil lead had a pin hole in it

[Riceburner]

I haven't checked the AFR's, the plugs had only been in for around 10mins and I was starting to get color. there's no spitting out of the carbs which it has done when it was lean previously.

 

It's consistent through the rev range.

 

I tried running the car in the dark to try and spot any misfires from the leads. I'm not sure if the end of the #6 lead coming off was a coincidence or the cause of the miss. I'll have to replace it either way, so I guess it'll answer the question.

 

Haven't checked for vacuum leaks yet, Thanks!

[zed74]

If leads 5 years old try another set...just in case

 

Top Gun pro series spiral wire 10mm

 

or MSD set

[Riceburner]

Perhaps it was just the angle I held the lead at when I tested it, forcing the faulty piece to make better contact and give a false 'good' resistance reading.

[PB260Z]

Hi

 

Sounds like leads or a plug to me. Have you tried removing the leads one at a time to identify the cylinder that has the fault ?

Once you identify that it is a particular pot, swaps that lead with another and see if the problem moves - if it moves then the lead if cactus.

 

Just a thought.

 

Cheers

 

PB

[Riceburner]

Hi PB, yeah it seems like it's cylinder six to me and that's the same one that had the lead end break off late today. I had new plugs so they were indexed, gapped and fitted. I don't have any spare leads so I'll get some made up at IC&E or Scorcher to suit the MSD.

[ZED83]

If its still missing after you've replaced the leads....

 

My bet its the MSD!

 

I had a 6AL brand new was making the engine hesitate (mi-nute miss) at any rev range. You could see it watching the tacho drop off periodically, not something that i wanted it to be doing at high RPM!!!

Edited January 5, 2016 by ZED83

[Riceburner]

Hi Owen, that doesn't sound too good. Here's hoping it's just the leads

 

I do have a back ignition module hidden in the car so I can switch to that if the MSD does fail.

[Riceburner]

I have changed the broken lead on #6 but it hasn't made any difference.

Checked the MSD and I'm getting huge multiple sparks at the plugs.

I checked the valve clearances and adjusted them on #6, this has made the misfire quicker. 

 

I'm going to check the clearance again and set them up loose. I always seem to set them too tight. My specs for this cam say 10thou, I'll aim for 12.

 

Could it just be valve clearances?

[PB260Z]

Hi Mate

 

If it is not the leads or plugs and you have a new engine with correct clearences, I would be getting sus of the ignition module.

 

Good luck

 

PB

[Riceburner]

Thanks PB, I'll switch to the back up ignition tomorrow and hope that's all it is.

 

Getting pretty stressed now, I've run out of ideas/knowledge and with a lot of money in the engine the only other thing I can think of is pulling off the head to check the gasket for leaks.

[peter mc]

Did you do a comp test ?? Next in my list would be inlet gasket leak at the head ..

[Riceburner]

Hi Pete, I tried spraying the inlet manifold with soapy water today but it didn't seem to make any difference to the idle speed or the misfire.

 

I have a comp tester somewhere will give that a try too.

[C.A.R.]

I'm wondering if a valve has kissed a piston...

[peter mc]

Soapy water wont tell you anything mate .do a comp test first if ok ..get a hose and listen for a leak at the manifold face

[EJ101]

can't wait to find out what it is..................sorry until you find out what it is

[Enzo]

Hi,

As Lurch has mentioned, a valve may have touched a piston bending the valve. This would cause the miss. If you has access to a video probe camera, remove the spark plugs and insert the camera tube. Look for any indentation or mark on the top of the piston. This should be relatively easy as the top of the piston should not be carboned up yet.

Whatever the problem I hope it's an easy fix.

David.

[Riceburner]

So the saga continues... Did a comp test, looks like I didn't disconnect the MSD properly and it turned into a smoke bomb! And now the car won't start via the push start button, YAY!

 

I managed to do the test with a screw driver on the starter, my battery is small so it was 3-4 cranks on each cylinder and I couldn't open the throttle. All cylinders were in the 140-150psi range, is that good with closed throttles?

 

So now aside from an expensive engine that doesn't work I also have a cooked MSD and a car that wont start.

 

For sale thread on the way!

Edited January 7, 2016 by Gareth. J.

[EJ101]

don't be silly. don't be like me!

 

you'll find the problem and it'll be like "oh yeah I knew that was it"

[PB260Z]

Two steps forward and one step back is the normal way of things with cars.

Don't do anything drastic, just walk away for a day, week or two and come back refreshed.

[Riceburner]

Tantrum over   I had a look at a few more things suggested on the following day.

 

I went to the FCR carbs, unfortunately due to the 'chatter' noise they make listening for air leaks was hard, especially with my partial deafness. I started pulling everything down including plug wires as the carbs are hard to remove and replaced the coupling rubbers on the manifold. Refitted them, put everything else back together and cranked. It ran, but really rough! Switched off and through the toys from the cot again! Lol.

 

A new day, a few more bits to remove and check again. I decided to check the manifold gasket after suggestions here. I removed the carbs, started on the heat shield and while glancing at the dizzy something caught my eye. #6&3 looked to be in wrong order, I switched them and decided to fit the carbs back on and try my luck.... "HUZZAH, it's alive!" was the first response followed by " you co%k head" and "oh the humanity".   

 

I had to alter the timing by a long shot as the new Bosch ignition system was different, Glad I left that in there. I called PMC (possibly should have done this sooner  ) to get some expert advice. It's sorted! 

 

So pros and cons...

 

Pros: I have a new 3.1L, PMC P90 head, 10.5:1 comp, 76 works high lift cam, CR gearbox, 4.375 diff, goes like STINK although with no tach (it's configured to run off the MSD) I don't want to rev it too hard to begin with! Not turned properly yet.

 

Cons: I have spent a week pulling my hair out, whats left is turning grey quickly, the swear jar has been replaced by a barrel, my MSD6AL-2 and the HVC-2 blaster coil are cooked due to my stupidity, about $600 all up

 

Many thanks to all who posted with advice and help, it's much appreciated!!! PMC you're a legend

It's invaluable to have such a great forum and so many knowledgeable members willing to give a helping hand when required. 

[C.A.R.]

Swapped plugs leads?!

Really?

 

Jeeze Gareth - noob mistake...