Pinto High Speed miss

[JHerscher]

I have a miss that I'm unable to trace and appreciate input and comments.

Van Diemen RF01
Pinto
Professionally built engine has approximately 4 competition hours - 3 weekends
Chassis underwent ground up winter 2013
Wiring all renewed/verified correct
Engine new for 2014 season.
Points/condenser ignition. (Please no debate around Pertronix vs points - I've used points for over 20 years with no issues)
Mechanical fuel pump

Good news is that this miss is reproducible in the shop. Bad news is that I've run out of things to try.

Miss is generally a high speed miss, starting around 5000 RPM, getting progressively worse as the upper ranges are reached. At 6500-7000 it has a "ba-da-ba-da-ba-da-ba" that almost sounds like a rev limiter. I don't have a rev limiter.

What I've done with absolutely no effect:
New points/condenser
Exchanged distributor
New Coil
New distributor cap, rotor, coil & spark plug wires
New Plugs
New Master switch
New Ignition switch
Bypassed all onboard ignition/starter wiring & replaced with mini harness made up for test purposes
Replaced Battery
Verified carb is correct - it went back to the engine builder who ran it on an engine on his dyno. Not the carb
Exchanged carb
Replaced fuel pump
Verified valve lash
Bypassed the Mychron dash - left it completely out of the system
Ran it on the onboard battery & the jumper battery separately
Replaced starter (really getting obscure here - possibly the big lug on the solenoid was arcing internally - it wasn't)
Replaced fuel lines
Verified the fuel level is correct in carb after hot cut.
Verified the fuel vent is working properly.
Fuel filter shows no signs of deterioration of cell foam


History of the miss:
-Weekend #1 - no problem
-Weekend #2 - Double weekend - No problem Saturday, started in Sunday's race.
-Miss was reproducible in the shop so between events, I tried a lot of things listed above and convinced myself it was the carb. Replaced the carb with another, and went racing.
-Miss was present through practice and qualifying on Saturday of the next event. Saturday evening, we replaced a fitting on the "hot" wire to the ignition, separated the plug wires a bit better near the distributor cap and replaced the plugs. Miss WENT AWAY for the morning race and came back during the afternoon's race.
-Shop running (2 weekends worth!) since to try to figure this out.

Any and all thoughts welcome. I'll even be open to the Pertronix suggestion if someone wants to lend me a distributor that's already set up. I'll pay freight both ways to/from 33907.

Thanks
John

[2BWise]

Just going to ask because its not listed but have you checked timing? The morning/afternoon symptom could be a result of temperature change affecting the prefer timing.

[Brian]

Bad valve spring? You always have to remember that a carb under load is running on a totally different part of the fuel curve compared to an engine free-revving under no load. Revving an engine to 6500 - 7000 rpm under no load is not a useful way to trace a fuel issue. Nor ignition, since the fuel/air ratio isn't anything close to what the engine would be seeing under load. But a bad valve spring is always a bad valve spring...

Edit - since we're thinking of valves, check cam lift. You might have wiped a cam lobe.

Brian

[Steve Demeter]

Are any of the plugs wet?

If only 1 is wet than that cylinder is the one to check out first.

Do you run a shift light, probably not with the AIM.

Do you run a rev limiter.

A really obscure thing I once had was that the slide on connector on the end of the wire from the condenser to the coil was not a tight enough fit and caused a miss.

Is the float level correct, could the float have a hole in it and be sinking.

[Rick Kirchner]

play in the dizzy shaft?

[Modo]

don't see different plug wires, coil-dist wire, unless u did this with distributor change, do dark room test, run in dark garage and look for blue arcing any and everywhere after 5000 rpm and miss, good luck ....................... had blue arc at Las Vegas Reg'l and didn't find it until dusk, was cracked weld on rollbar, was the ground strap to rollbar brazing n crack, official said I see u got your power back the next day!!!

[rickb99]

Sound exactly like the problem we had when two tiny pieces of fuel cell foam made it in to our in line filter. But, you said you had checked that. Is there more then one filter in your fuel line??

[JHerscher]

Most of the questions/comments were addressed in the original post. Please re-read if you're not sure.
Those were: rev limiter, Plug wires/cap, distributor play (exchanged distributor). Condenser is new.

Brian - Valve spring - why would it disappear and come back? Besides - just a few hours off a rebuild? Cam lobe? same question.

No wet on any plug

dark room check was performed.

Timing was one of the first things I checked - forgot to list as it was pretty obvious. Also did a leakdown - 2% leak across all four.

[tombeattie]

Any and all thoughts welcome.

Thanks
John

Hi John,

Crappy fuel?

Tom

[JHerscher]

Hi Tom

Not likely - same jug as when it was "fixed"

[Modo]

You need to move out of Ft. Meyers, Fl, that's the problem .......not doing well on these lately, good luck J, let us know!!

[BURKY]

Bad ground?

[Bob Coury]

If you purchased the plugs by the box, were they all out of the same one? Years ago in my FF, I spend a week troubleshooting a no start/miss condition. Kept trying brand new plugs of the correct heat range from 2 boxes. As a last resort, I put in the plugs from the previous season (by a different mfg) and the problem went away. Too easy. Re-installed plugs from the new boxes and the problem came back.

I doubt that is it, but it looks like you tried just about everything.

PS Modos/Burky's suggestions looks like they are worth looking into.

[sracing]

Disconnect the tach (all 3 wires) and try again. (The tach is connected to the pulsed primary ignition line and can short internally, causing a miss. Even if that isn't the problem, when connected it will give you some info. Watch the tach when it starts the miss. If it is a primary ignition issue (distributor, coil, points, condenser, or primary wiring) the tach will jump around erratically. If the tach only continues to read without jumping around much, you have a fuel or secondary ignition problem.

If you say it fails in the shop (I assume not on a dyno) with no load, this is really a weird one and almost HAS to be in the primary ignition side. Any fuel or secondary ignition (high voltage) issue would be far worse on the track at higher cylinder pressures and would probably not show up under no load conditions at all.

Know anyone with a scope? A cheap O'scope or auto diagnostic scope would show this up easily. BTW, replacing all that stuff at once is SOMETIMES the right thing to do, but it also greatly increases the odds of putting a defective component back into the system. Since you have the ability to make it fail in the shop, it is far better to just replace one or two things at a time and check results. Also there are several things that could be done first to at least put you in the right area of what to replace rather than the shotgun approach.

Best.

[Northwind]

It's been about twenty years since I have had a pinto so my memory may be way off on this one. Mechanical fuel pump plunger rod worn? It causes the fuel pump to short stroke and not move enough fuel.

[JHerscher]

Chassis/engine ground is good - specific ground strap between chassis & engine, clean contact.

Four sets of plugs have been on the car, two sets used, two sets new. All read well. New plugs all matched.

Parts were exchanged/replaced one at a time. I've played this game long enough to keep from driving myself nuts that way! Not to mention the $$$!

As noted in the original post, Mychron components including tach were completely disconnected from the system; that is to say there were only four wires plus the battery & ground strap connected to the car.
- hot to starter button
- jumper from that terminal to the hot side of the ignition switch
- wire from the starter push switch to the solenoid to start the car
- wire from the ignition switch to the coil to run the car.
All new wires/connections. New ignition switch, existing starter switch.
Tach did not jump as the revs were increasing.

I even took the transponder out of the system on the thought that there might be an internal short.

Car would not run at all well at the track - far worse under load. It took forever to get the car to 6800 on track; in the shop it gets there pretty quickly but has that ba-da-ba-da thing going on while it gets there.

Only the single fuel filter that I can access.

I thought about this last night - on my last cell there was a pre-filter inside the cell at the end of the inlet fitting that I expect is also on this cell. It might be the problem. I'll get a 5 gal jug of fuel and stick the fuel feed line into it to verify that.

Edit - thanks to all for the input.

[Modo]

blow air back into cell and see if problem clears up, sediment around filter in fuel bag, used to do that in my British sports cars, would clear up for a while, .............also go without your external filter if u havn't already, can always clean carb if need too, easy!! I never used fuel filter although one is built into my current electric pump 'blue' from the Peg.......

like Kentucky's reasoning above though, not fuel I believe

[JHerscher]

Thanks for the comments. I agree, it seems electrical versus fuel. I bypassed the cell this morning and went straight to a fresh 5 gal jug of AVGas 100LL purchased this morning. No difference. I am about to see when my buddy who has a pinto FC in the same shop complex as I am is out of town for a few days. Let's see. Disconnect and swap two engines should take how long?;)

[ajpastore]

Have you checked battery voltage with the car running? AND at the coil? I see you replaced the battery but I didn't see any numbers.
-A

[Pi_guy]

There was a F2000 car at this last race at Thompson that had a miss in one or two cylinders. Must time was spent trying to solve the issue by much of the brain trust at the track. It totally failed <pulled apart> in the 2nd qualifying session on Sunday. It turned out to be the connector from the battery lead to the master switch it had been sort of making contact by being held in place by the shrink wrap, but under load it developed a miss.
They finished the race on Sunday with no issue present.

[Nardi]

This thread has proof that Modo can make comments that can be understood!

[DaveW]

IMO, the fact that you can reproduce this in the shop eliminates almost all fuel problems. If it is the same under load (high fuel flow) and under no load (very-low fuel flow), it is not related to fuel flow issues such as filters, etc.

[HayesCages]

We had exactly the same problem, worked on it an entire triple race weekend with no fix. Turned out to be the crappy hardware store switch on the dash. I know you said it had been replaced but with what kind of switch?
We now only use Mil-Spec type switches with screw terminals, no spade type at all...
Just an idea.

Good luck!

[Pi_guy]

We now only use Mil-Spec type switches with screw terminals, no spade type at all...
Just an idea.

Good luck!

Most people flip out at the cost of the switch. It is the only ones I carry.

[HayesCages]

Aye, but it's a small price to pay in the end!

[Pi_guy]

Aye, but it's a small price to pay in the end!

Too often the "Penny wise pound foolish" phrase comes into play.

Made a comment to a driver about Ty wraps, that the ones with the metal tang were better. He responded with I only use them to hold wires what can go wrong.

[HayesCages]

Exactly. What on Earth could ever go wrong in a highly stressed racing car?
Everything, that's what.

[JHerscher]

Mil-spec switch. I've been down the auto parts store switch road and learned my lesson 10 years ago.

Keep the thoughts coming.

Thanks
John

[HayesCages]

Is your engine the same color as that other guys? I say go for the swap and let him figure the miss out...

[JHerscher]

No but I do have a can of paint....

[Pi_guy]

What I would do if in same room, often hard to pin point from miles away.

Load test battery
then I would load test every large diameter wire connection
starter terminal, master switch and secondary battery connection
I would look for the rate that the meter swings <analog>
If that proved faultless I would run car and load test from secondary battery connection and see if miss appeared.
ONLY LOAD TEST LARGE DIAMETER WIRES & battery

If not then I would get analog voltmeter with alligator ends pick a voltage connection point and do a wire shake test -- I would continue with different connection points until problem was found.

If no problem was found I would look towards a EMF and RF meters to see if a signal is being induced from some other source.
<we found as insulation breaks down on starter motor power lead it induces noise in to crank pick up, a EMF meter will show the field about the wire>

If that fails repaint motors proper colors and swap with garage mate.

If all that fails come ski racing with me there are very few wires, only in Timing section.

[jnortonjr]

1. Verify camshaft and crank timing marks.
2. Verify ignition timing at 4,000 rpm.

You said the engine was professionally built. Have you contacted the builder to inquire? Did the builder place a TDC and advance mark on the flywheel? Is the camshaft on an adjustable pulley?

John

[Purple Frog]

Check cam timing. A well placed stone can cause the belt to skip a tooth.
Broken or weak valve spring. Wiped cam lobe (mentioned before)
Bent valve...maybe do leakdown.

[JHerscher]

Thanks for the thoughts.

The biggest question for me:

Why did it disappear for 30 competition minutes after changing plugs, separating the plug wires and replacing the hot wire fitting (which upon dissection was determined to be good) and then reappear? Seems as if it might have been plugs, right? I've changed to two other sets since then (one new set, one used set). They all have looked normal. Yes they are the correct heat range.

Before anyone suggests replacing the primary ignition wire, note that it has already been done. I bypassed the entire wiring harness.

Yes all timing marks are correct.
Yes I've contacted the builder. Mike, you know who I use.
Not adjustable cam pulley.
As noted above, leakdown numbers are sensible.
Multiple batteries were used as were multiple battery heavy gauge wires and grounding points.
All with no discernible difference.

One might say that I am a little bit frustrated!

Off to Asia for a few weeks to ponder this some more. I think I will break the car in two and see if the gremlin can be identified with the engine separated from the chassis. Maybe even set up a "run it out of the car" framework to safely assess if it is chassis or engine related.

Happy days.

[R. Pare]

What brand of plugs? I've seen "new" plugs start arcing through the ceramic to the steel body very early in their life, causing this exact issue ( Champions). Found the issue strictly by accident when popping the hood just after dark.

[Purple Frog]

How soon you leaving? I'm in Miami
could drive over for a day to really confuse the issue.
eight 5 0- five 7 0 - frog

[mahodges]

I had a similar problem and it turned out to be a broken valve spring. Easy to remove the valve cover to check.

[EPRacer]

John:

Changed the lock to shop door!!

Lyn

[JHerscher]

An update. For those who were convinced that it had something to do with a bad valve spring or a wiped cam lobe, we can write that off the list of possibilities. I pulled the head and sent it back to the engine builder who has been aware of the issues. Basically checked out ok. No mechanical smoking guns. He said the valves needed a touchup and two of the springs were a couple pounds off, but nothing that would cause my problem. He brought everything back to spec. So the good news is that I now have a fresh head. The bad news is that it did not fix the problem.

For those of you who wonder if the engine builder knows what he's doing, this is someone who builds engines for readers of this forum in multiple classes. FV FF FC.

I see an unanswered question I missed about spark plugs.

NGK AP8FS

So the season is over for me and I will perform a winter teardown to see if the cause can be identified.

Of course if anyone wants to lend me a good engine to try in my chassis, I'll be happy to oblige!

Ideas are always welcome.

Thanks to all fo rthe input.
John

[Bob Coury]

Did you see my post as well as R. Pare's? If you haven't done so, I would throw in some used plugs from the previous season and see
What happens.