Mystery Motor Mutation

[stretchit2]

Last Saturday took the Healey out for a ride. She ran great until......accelerating uphill on the freeway at about 70 miles an hour I hear a rapid fire pap, pap, pap, pap, pap, pap, pap. She doesn't lurch but she won't accelerate. I exit the freeway and she runs just fine.

So I think fuel, but knowing 90% of fuel problems are electrical, I think ignition. So I go for the low hanging fruit and change out the condenser. I then take about a ten minute drive back to the scene of the crime (uphill climb on the freeway at 70 miles an hour) and .......pap,pap,pap,pap,pap,pap. I exit the freeway and once again she purrs all the way home.

It only seems to happen going uphill, under load, at high speed.

A little background, the Healey is a tri-carb, well maintained and generally runs like a top. Several months ago I had the distributer rebuilt by Advance Distributer which really made a difference in the cars performance. I had been running Pertronics prior to the rebuild, but when Advance rebuilt the distributer they really encouraged me to go back to point.

Any thoughts

 

[DerekJ]

Fuel pump problems?

When you say 'pap.pap, pap'...are you saying it's a regular noise or is it a stuttering, jerky motion that you get with fuel starvation?

 

[Bob_Spidell]

I have two guesses:

1) ignition. Distributor rebuild notwithstanding, the problems starts with heavy load (uphill, etc.) which could mean you have marginal spark. Leaky distributor cap?
2) fuel starvation (but doesn't explain the problem only occurring under load)

 

[andrewss]

Had a similar problem last year in a BJ7. Endless hours checking and found that the fuel pipe under the car had been 'squeezed' by a car jack and as a result fuel flow was compromised. Uphill the SU carb did not have the pressure to manage the additional fuel required... on the flat it was fine.

 

[stretchit2]

Fuel pump problems?

When you say 'pap.pap, pap'...are you saying it's a regular noise or is it a stuttering, jerky motion that you get with fuel starvation?

I "think" it was more about the noice, although I was loosing power I don't remember the sensation of a jerky motion. I did clean the fuel filter and made sure all the fuel lines were attached properly. I do have a spare fuel pump, I could throw that on to test to see if that is the problem.

After work naturally, someone needs to pay for all these Healey parts

 

[Healey 100]

Could be not enough point dwell. Make sure the point gap is on spec. It does sound like an ignition problem. Fuel starvation usually gives you surges or engine dying, not misfire under load. What kind of ignition wires on the car and how old are they? Carbon "wires" can act funky under load and are hard to diagnose.

 

[LarryK]

Check fuel pressure before removing could be low and float levels could be a tad off. Check timing and ignition as points could be too wide. Lots of variables but a recheck might find source. When adjusting points always recheck timing. If you can find or have a vacuum port, this can help with the micro adjustments. You are not experiencing jerks, I would start with fuel.

 

[AH100M]

My bet's on the coil.

 

[Deleted member 8987]

Always the coil. Change it out to help support the PRC coil manufacturers, then find out that wasn't it after all, and now you have a spare coil!

 

[stretchit2]

Always the coil. Change it out to help support the PRC coil manufacturers, then find out that wasn't it after all, and now you have a spare coil!

HA HA HA! That is funny

I believe the mystery has been solved.

And the answer is.............envelope please.....

TADAAAAAA .......... FUEL PUMP!!!!!! Who would have guessed the rare 1 out of 10 times that a fuel problem actually turns out to be a fuel problem. After work I changed out the fuel pump took her back to the scene of the crime (high speed, uphill, under load) and she ran purrrrrrrrfectly. I took two more runs on the freeway uphill and couldn't recreate the pap,pap,pap,pap,pap, nothing doing, just the beautiful exhaust note of a Healey. YEAH!!!!!!

Thanks to everyone on the forum for your sage advice.

Cheers,

Jeff

 

[TimK]

It is always fun to learn what the real problem was after reading all the ideas of what it could be. It is amazing that our cars run at all after all these years with all the things that can (and do) go wrong with them. I've had mine for 33 years and never had a fuel or ignition problem (except for a new fuel pump) -- but only driven about 7,000 miles in that time.

 

[Bob_Spidell]

... It is amazing that our cars run at all after all these years with all the things that can (and do) go wrong with them ...

OTOH, in some ways the very simple and relatively robust components in older cars like our Healeys make them (potentially) more durable. Just watched a show called 'Modern Marvels' that documented some catastrophic failures in semiconductor parts--like in extremely expensive satellites--caused by 'tin whiskers,' a crystalline growth from the tin that is used to solder and shield miniscule components that can cause a short. I dare say our Healeys will never suffer from such afflictions, not having many, if any components with tin in them (unless your car has an aftermarket electronic ignition, fuel pump, etc.).

There's no reason Healeys can't run forever--barring some inevitable issues like frame degradation from rust and fatigue--if they are properly maintained. That's the advantage of more modern cars--relatively less maintenance required--until they fail, then good luck finding and fixing the problem, especially if you don't have the sophisticated (read: expensive) diagnostic tools required. My folks' 2002 Lincoln LS would occasionally die for no apparent reason, then start and run fine after a 'rest.' Turns out it had a well-known problem with on-plug coils that created a voltage spike causing the ECU to go into shock and shut down. Won't have that problem in a Healey though, it seems, coils are always getting the blame when no one can find the real problem.

 

[Keith_M]

To extend Bob's comments a little, a large part of the appeal of these cars for me is their simplicity (besides the obvious things like styling, exhaust note, etc). I rebuilt/restored pretty much everything on my car, and as a result I understand how everything on the car works. There are no 'black boxes', computers, or circuit boards; everything is understandable by a weekend hack mechanic like me. When everything is working, the sense of satisfaction is overwhelming. If something goes wrong I can diagnose and fix it, and even that is a very satisfying feeling.

Based on your last post, Jeff, I'm thinking you experienced that satisfying feeling when you solved your problem!

 

[stretchit2]

To extend Bob's comments a little, a large part of the appeal of these cars for me is their simplicity (besides the obvious things like styling, exhaust note, etc). I rebuilt/restored pretty much everything on my car, and as a result I understand how everything on the car works. There are no 'black boxes', computers, or circuit boards; everything is understandable by a weekend hack mechanic like me. When everything is working, the sense of satisfaction is overwhelming. If something goes wrong I can diagnose and fix it, and even that is a very satisfying feeling.

Based on your last post, Jeff, I'm thinking you experienced that satisfying feeling when you solved your problem!

Keith - Like the man says, "Even a blind squirrel finds an acorn every once in a while." I have to say the Austin Healey folks, both on line and with our local group, are incredible. Everyone is helpful and generous with their time and talent, so it gives a hack like me a safety net of knowledgeable people who can bail me if my tinkering gets me in too much trouble.

Cheers,

Jeff