Jump to content

Power loss around 3000 RPM


Recommended Posts

13 hours ago, midlife said:

I'm placing my bet on the carb: that the secondaries aren't opening due to some mechanical interference or lack of vacuum.  Yes, I know carbs were swapped, but the symptoms just reek of lack of fuel.  JMHO.

He can check if they're opening by placing a paper clip on the vacuum rod at the top and seeing if it has moved down after a drive. I believe he said the 4160 had vacuum secondary's. It's a weird issue for sure, but likely something simple and overlooked by us all.

Geoff.

 I learn something new every day!

Link to comment
Share on other sites

I do have one other idea based on something new mentioned - You have the operational ram air. Have you tried running without that, maybe put on a open air filter? I saw you tested it, but perhaps the issue isn't fuel starvation but maybe there's some vacuum issue under load that is allowing all the flaps to close and its starving for air under power. Maybe a failed or disconnected vacuum canister. 

The FMX has nothing electronic in it, its  just a big hydraulic pump. Failure = not shifting or slipping. Anything that would limit rpms at this level would make horrific noise. I even tried a search on the web and couldn't find a single reference to a non-electronic transmission causing the conditions described, always the reverse due to slippage.

These cars are simple air pumps honestly. Air/Fuel in, combustion, Exhaust out. To oversimplify, The vacuum indicates the engine is in good condition as stable vacuum in a strong range. Your exhaust is free. This leaves 2 options - air/fuel or ignition. 

Something is failing under load or heat. Could be as simple as not having a resistor on a coil that requires one and the coil overheating. Bad plugs, wires, cap, timing, etc. Or both the current and replacement part have the same problem. Replacing with another one will produce the same results (Ask me how I know). I even considered a rev limiter (My MSD has one) but the OP has pertronics.

My money is on fuel. In the garage the car can keep enough fuel for revving above the 3k rpm mark. Under load at steady speed the engine consumes more fuel and its not happening. 

I had similar issues and had just replaced the entire fuel system - tank, lines and carb. Nearly $1000 so there shouldn't have been anything wrong.  I had put on a gauge and pressure was stable 6.5 lbs.  It would run for awhile but lose power after a few miles. I could run it in the garage for hours without issue. Out on the road, it would die again after a few miles. 

Turned out after 2 weeks of testing and trial and error to be vapor lock caused by a number of smaller problems. The fix required removing the clear fuel filter (They cause a low pressure condition)removing the mechanical pump, installing an electric pump at the tank to pressurize the lines, a heat shield, spacers and insulating lines in the engine bay. Granted I live in a much warmer climate but just drove almost 100 miles yesterday in 95+ heat with the AC on and haven't had an issue since I made those changes. 

Stick will air, fuel, spark and you will track it down!

  • Like 1

 

My_Vert_Signature.jpg.be46b029936118552aebff3a5a6ae997.jpg

1973 Convertible : 351C, FMX, Factory AC, PS, PB, 2.75 Rear Ratio

 

Link to comment
Share on other sites

Did you try closing the spark plug gap to .035? This certainly is an odd one. You may want to check the coil wire to see if the connector made it through the 90 degree boot turn and is fully seating in the cap, yeah it is a long shot but at this point........  Chuck

Link to comment
Share on other sites

Stanglover - once I get time, will check the secondaries again. It's worth a try.

Mezell29 - I cannot disagree with anything you said, it has to be fuel, spark or air - I did check to make sure all the ram air hardware is correctly operating. I've fought issues with vapor lock and fuel boiling with the vette, and used a heat shield and return line to successfully deal with it. This behaves a little different, it is very consistently RPM-related when the car is under load. I want to lean towards fuel as well, but we'll see.

c9zx - I did check gap, it is .035, and just for shits and grins, threw a new coil, plugs, etc in - no change. I did not check the coli wire, though - will do that ASAP.

Black 1971 Mach 1

351C/FMX/TrickFlow Heads/Lunati Retro Roller Conversion

Classic Auto AC, Manual Front Discs, Upgraded Springs/Shocks/Close-Ratio Steering

 

IMG-2977.jpg

Link to comment
Share on other sites

Years and years like 35 years ago my 72 was running poorly over a certain rpm. Turned out to be bad wires, never forgot this since my friend and I were randomly poking around one late night  and saw plug wires  arcing in the dark. Very hard to see but for sure arcing. Course the plugs wires then are  nothing like today's.  Just a thought.

Link to comment
Share on other sites

Just trying to throw anything out there.  Does any ignition component you're running have a rev limiter capability that can be modified by the user?  Maybe it somehow became accidentally set to 3K rpms.  Of course that still doesn't jive with the fact that you can downshift to second gear and take it up to 4K rpms.  Is that still true?

Link to comment
Share on other sites

Donkost - I've never heard that the pertronix has a rev limiter. On the 4000 RPM in 2nd, it was true last time I tried,that was going into the weekend. AS I said before, I'm reluctant to push it too hard till I understand more,simply on the off chance it's not just air/spark/fuel. 

I tried a couple of the other suggestions last night with no joy. This afternoon, I am taking the car to a local mechanic who does a lot of the classic car work here in my hometown. I'm sure I missed something basic, but just don't  have the hours to spare right now, between work and other home projects I need to focus on. Time to let someone smarter than me take a crack at it.

Once he finds what  I missed, I'll post it here.

 

Black 1971 Mach 1

351C/FMX/TrickFlow Heads/Lunati Retro Roller Conversion

Classic Auto AC, Manual Front Discs, Upgraded Springs/Shocks/Close-Ratio Steering

 

IMG-2977.jpg

Link to comment
Share on other sites

7 hours ago, donkost said:

Just trying to throw anything out there.  Does any ignition component you're running have a rev limiter capability that can be modified by the user?  Maybe it somehow became accidentally set to 3K rpms.  Of course that still doesn't jive with the fact that you can downshift to second gear and take it up to 4K rpms.  Is that still true?

I thought about this too - I have a MSD with a rev limiter but the OP had a Pertronix. Unless that unit is bad somehow. I ran one in another car without problems but a failing unit could cause it. I am really curios about the solution to this one. I do a lot of really techie stuff and I have to solve a mystery!

 

My_Vert_Signature.jpg.be46b029936118552aebff3a5a6ae997.jpg

1973 Convertible : 351C, FMX, Factory AC, PS, PB, 2.75 Rear Ratio

 

Link to comment
Share on other sites

Which pertronix module are you running? I, II, or III? The III is junk and will cause this issue. 

73 Grande H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

 

- Jason

 

 

082-hot-rod-power-tour-2017-1970-1970s.jpg

 

Link to comment
Share on other sites

26 minutes ago, 73pony said:

Which pertronix module are you running? I, II, or III? The III is junk and will cause this issue. 

it's not the III - I'm sure its the first-generation ignitor, it looks like a little black square module.

Black 1971 Mach 1

351C/FMX/TrickFlow Heads/Lunati Retro Roller Conversion

Classic Auto AC, Manual Front Discs, Upgraded Springs/Shocks/Close-Ratio Steering

 

IMG-2977.jpg

Link to comment
Share on other sites

Ok was just checking. 1st gen is good. 2nd gen is good as well but you have to either run via relay or bypass the resistor wire to get a full 12V to the coil. The 1st gen will run on the reduced voltage of the resistor wire without modification but the 2nd will not run properly and the 3rd is garbage, ask myself and several other members. I had a III and after about 800 miles it started doing as you describe. Basically it was not holding timing. Would idle fine but when reving under load the timing would fluctuate all over the place.  

73 Grande H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

 

- Jason

 

 

082-hot-rod-power-tour-2017-1970-1970s.jpg

 

Link to comment
Share on other sites

If it cuts out almost precisely at 3K rpms in a predicable manner, it almost seems like it has to be ignition-related.  That thought and 2 bucks (or whatever it is now) will get you a cup of coffee in any US diner.  lol  I used to troubleshoot this type of stuff in the early 80's when I tried to do all of my own work to save money I didn't have.  I had the plug wires arcing issue once that someone else described earlier.  I worked at a regional auto parts chain and had full use of a unused four-bay shop in back with a lift, plus unlimited parts access.  19 years old and no other responsibilities, sometimes I miss those days.  ha  Anyway, I'm thinking that if it was a fuel or carb issue and the car is being driven in different temperature ranges, this issue would not repeatedly occur at 3K rpms.  Keeps coming back to ignition in my mind.  It will be interesting to see what the pro mechanic comes up with.  Probably similar to your current situation, now I have plenty of money but no time.

  • Thanks 1
Link to comment
Share on other sites

I took the  mustang to a local mustang guy - he called me back convinced it is fuel starvation. he took  the car  out, ran it until the power loss happened,then shut the car down. The fuel bowl on the carb was nearlyl empty - it would barely squirt gas when the throttle was manually rotated. This is  unlike at idle, just after starting, it is full and has a healthy squirt (he checked). 

Before going further, he called me and walked me through what he did - then, knowing I do a lot of my own work, he wanted to know if I wanted to take it from there. His opinion was carb needle and seat were sticking, or I had a (second) weak pump. He was leaning toward carb because of the pump swap, as was I, so I decided  to  take the car home and started in Saturday morning. 

I pulled the carb and cleaned it up - I did find a seemingly sticky needle. Put it together, and sonofabitch, same problem. Tried a third pump (not stock - an RPC 80 gph pump). No change.

I then tried a 3rd carb (I have a shelf full of 3 or 4 holley/QF carbs and a couple quadrajets). It actually showed improvement with a 670 cfm QF carb - but still had the power loss, just a bit later in the RPM range.

By now I'm ready to explode. Went  inside, watched a little TV with the wife,who was being exceptionally patient with me. I decide to goback to  square one. I had blown the lines out and was sure  they were clear,but there had to be a blockage somewhere.

Started a fresh inspection of my hard lines and eventually found this where the hard line passes through the wheel well:

 

wheelwell.thumb.jpg.8261f3042fec17c9ac66adc59a994747.jpgkinkedline.thumb.jpg.fb8f3fd6e7394d26f09710ef7f72d472.jpg

I missed it before, probably because the kink is back in the recess next to the spring,and was hard to see. All I can figure is that when I put the trans in, I must have pushed against the line and bent it.

The line isn't blocked, it will passs fluid and air, but that has to restrict flow - any feedback/thoughts on this being the cause of fuel starvation?

 

 

Black 1971 Mach 1

351C/FMX/TrickFlow Heads/Lunati Retro Roller Conversion

Classic Auto AC, Manual Front Discs, Upgraded Springs/Shocks/Close-Ratio Steering

 

IMG-2977.jpg

Link to comment
Share on other sites

I would say that you found your problem.   You are just plan ass running out of gas with the line like that.    Based on the diameter of the line vs it's now rectangle shape you lost close to 65% of the flow.   Sorry to see you go through so much work trying to find the problem but at least now you know what caused it.

 

Edited by Kilgon

Kilgon

 

 

"The only dumb question is the one not asked"

Link to comment
Share on other sites

I hope this is it - don't see how this isn't a problem. I've been saying I'm missing something basic or simple. However, I've just had so many options that didn't pan out that I'm just not feeling confident this will solve it.

Black 1971 Mach 1

351C/FMX/TrickFlow Heads/Lunati Retro Roller Conversion

Classic Auto AC, Manual Front Discs, Upgraded Springs/Shocks/Close-Ratio Steering

 

IMG-2977.jpg

Link to comment
Share on other sites

32 minutes ago, 71coop said:

I hope this is it - don't see how this isn't a problem. I've been saying I'm missing something basic or simple. However, I've just had so many options that didn't pan out that I'm just not feeling confident this will solve it.

Look at it this way.  That is the first real  problem you found so odds are it is the problem.  

Edited by Kilgon

Kilgon

 

 

"The only dumb question is the one not asked"

Link to comment
Share on other sites

I sure hope that's it.  From working in IT for 30+ years, it seems you have found "a" problem but possibly not "the" problem.  Still seems odd that this kink would cut off right at 3K rpms but allow up to 4K rpms when dropping down to second gear.  Well I guess you have to replace this section regardless and hope for the best.  I keep thinking about the trans itself but that makes no sense whatsoever.  This is not by any means a car controlled by computer modules.  It's great for that reason, but it sure wouldn't be a bad thing in this case to be able to plug into a OBD connector and see some errors.  lol

Link to comment
Share on other sites

DonKost, I get that, and my fingers are crossed. I

On  running up to 4K in 2nd - I thought about that as well.  All I can figure is maybe in drive at cruise, I'm not opening the secondaries yet, and  running the primary dry,  where in 2nd, I'm just loading the car faster, drawing on my secondary before running out - its entirely possible that had I continued to push this, the car would have fallen on her face just like in Drive. Of course, that's pure speculation. 

One thing is  certain, if this doesn't resolve the issue, I have to move on from fuel starvation as a cause. I'm going  to repair this and see - not sure what else I can do.

Edited by 71coop

Black 1971 Mach 1

351C/FMX/TrickFlow Heads/Lunati Retro Roller Conversion

Classic Auto AC, Manual Front Discs, Upgraded Springs/Shocks/Close-Ratio Steering

 

IMG-2977.jpg

Link to comment
Share on other sites

Just FYI - fuel line is 3/8 dia.  which = .110 sq inches .   Looks like line is at least 50%  pinched making a 3/8 x 3/16 rectangle.  This give an area of .070 sq inches.  Difference of .04 sq inches or 37% smaller. If that doesn't cause a problem I don't know what would.   Have faith and think positive! :biggrin:

Edited by Kilgon

Kilgon

 

 

"The only dumb question is the one not asked"

Link to comment
Share on other sites

Yep, that was it. Thanks everyone for the input - I appreciate it.

Now just need to dial that carb in.

Edited by 71coop

Black 1971 Mach 1

351C/FMX/TrickFlow Heads/Lunati Retro Roller Conversion

Classic Auto AC, Manual Front Discs, Upgraded Springs/Shocks/Close-Ratio Steering

 

IMG-2977.jpg

Link to comment
Share on other sites

Easy fix, it only took me about 3+ weeks to figure it out. I missed it twice.

Black 1971 Mach 1

351C/FMX/TrickFlow Heads/Lunati Retro Roller Conversion

Classic Auto AC, Manual Front Discs, Upgraded Springs/Shocks/Close-Ratio Steering

 

IMG-2977.jpg

Link to comment
Share on other sites

Great work- yes took a few weeks but this was no doubt in your spare time.  Your second gear theory makes sense as well.

  • Like 1
Link to comment
Share on other sites

8 hours ago, 71coop said:

Easy fix, it only took me about 3+ weeks to figure it out. I missed it twice.

I just meant once you found the crushed line it was easy enough to fix.

 I feel your pain, had a brand new sew of lifers go bad and took me a few weeks to go thru everything to figure that out. I thought I had bad gas, or a carb issue, or something wrong with the ignition system. I definitely learned a few things along the way too,. 
 

Anyyway, just glad you figured it out, it can definitely be frustrating! Now, time for some cruising. 

  • Like 1

John - 72 Q Code

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...