Power loss around 3000 RPM

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Kilgon

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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.

 
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71coop

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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.

 

Kilgon

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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.  

 
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donkost

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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

 

71coop

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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.

 
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Kilgon

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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:

 
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71coop

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

Now just need to dial that carb in.

 
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71coop

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

 

donkost

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

 
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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. 

 
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Yes indeed, so glad you found it. Frustrating for sure, but satisfying at the end of the day. However, thinking back, NONE of us thought of looking for a crushed fuel line, everything else under the sun, but........

As a suggestion and from my own findings, think about replacing ALL the lines with 3/8" SS if you have not already done so. Rust builds up in them and that caused me to have fuel related issues. I know you've spent a ton of money lately, so maybe  a next years project. Unfortunately, I could not find a 3/8" SS line from pump to carb, so I made one up from copper lined steel fuel line, connecting to a Holley thing-a-ma-jig. Here's a pic, you know what I mean, having a mind blank. Use Fuel Injector rubber hose as well, ethanol resistant and proper fuel line clamps, no gear things. PM me if you need specific details.

IMG_0979.JPG

 

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mjlan

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Plumbing in a temporary fuel pressure gauge at the carb inlet after you fix the kinked line would confirm that the pump can keep up with the engine's fuel demand.

 
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I was following this thread closely. I am glad you found it and solved the problem. Excellent case study for publication.

Sent from my SAMSUNG-SM-G930A using Tapatalk

 
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I thought I'd mention, that with 3/8' line all the way to carb, stock line to car from pump is 5/16", and in my case, a Holley 670 S/A carb, I can rev all the way up to 6K between shifts. That's with a 4 speed of course and no, I don't pull it that hard often, but it will go there. 5K is often!!

 

71coop

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Geoff, It doesn't look hard to replace the tank-to-pump fuel line, especially since it's in 2 pieces. I may put that on my winter list. On the subject of fuel line replacement, I currently have the QF carb set up with a braided SS hose from pump to carb, so replacing that will be the next thing. The braided hose with AN fittings was a temp setup to get the new carb in. I much prefer steel line. 

 
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Geoff, It doesn't look hard to replace the tank-to-pump fuel line, especially since it's in 2 pieces. I may put that on my winter list. On the subject of fuel line replacement, I currently have the QF carb set up with a braided SS hose from pump to carb, so replacing that will be the next thing. The braided hose with AN fittings was a temp setup to get the new carb in. I much prefer steel line. 
Yes, not too hard to replace that line, however on the one I got from NPD, I had to twist it at the tank end to get it to line up with the sender. However, that could have been damaged it shipping because the line is not well packaged, Other than that, no problem. I did add a small piece of rubber and an extra clamp. Pics later as I need to resize them along with most of my pics!! On the pump to carb line, I used a short piece of rubber to make the transition from the pump to the 3/8" line and also to act as a vibration damper. More later if needed when you get to it next year.

 
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On the fuel line diameter. A friend of mine has a 66 GTO with two 1,000 CFM dominators he has 5/8"  fuel line. In each 1/4 mile pass with burn outs and drive back he burns 5 gallons of the expensive racing fuel. His engine block was made by Jack Roush and is Pontiac. It is 18.3 to one compression. He is going to sell the car soon he say has had for 35 years. Does over 160 mph in 1/4 mile. It is a monster makes ice on the intake it flows so much air. 

 
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I'm trying this one again now that the dust seems to have settled with the forum upgrade.

I'm fishing for ideas and feedback on the problem described below. About 2 weeks ago, I started noticing a drop in power cruising on the highway - it manifested as I slowly accelerated to pass traffic in a 4-lane highway. RPM dropped to around 2500, it felt almost like I was running out of gas, then recovered after a few seconds.

It seems to be load related. I can manually drop into 2nd, push the car up to around 4000 RPM or better, and if I hold that a bit, the same thing occurs.

I can run the car up to 3700-3900 RPM in park and it revs just fine. Take the car on the road accelerate to 3000-3200 in drive, and it wants to fall on its face.

I have gone over the fuel delivery from end to end. I swapped carbs with a spare, replaced all the old rubber (most of it was not really old, but it was cheap), replaced the stock pump with a stock replacement (only $20 and was not sure hold the pump was anyway), checked the hard lines, replaced the filter, and pulled the sending unit (it was clean, the PO had replaced both tank and sender a few years ago).

I tried a new coil, temporarily swapped in a replacement Pertronix module, and both checked/re-gapped my plugs to .035, then just for shits and giggles, replaced them (yes, checked the gap first). I made sure my timing did not change (I run around 14 degrees initial, all in @ 35/36 @ 2800). Vacuum adds about another 10-12 degrees,an have always run it off manifold vacuum.

I pulled the valve covers and did find some evidence that some valves are rotating as if insufficient seat pressure. I changed springs to a little stiffer set, seat pressures is close to 125 installed.

I road-tested after each change and found that nothing actually had any effect on the symptoms whatsoever.

Last night I realized I had not looked at the radiator fluid, and found it was a little low -I am not sure it's related, but now wondering if I have a small head gasket leak. The car has not overheated. There is no evidence of any coolant leaks, and oil level is normal. No evidence of oil/coolant mixing anywhere. If it is a leak, it has to be coolant leaking into a cylinder and small so it doesn't effect performance at low RPM (below 2500).

When putting a vac gauge on the motor, Idle vacuum holds steady at 16 Hg, which I think is to be expected with my cam profile, and I see no unusual behavior suggesting valve float when revving up to 3700 RPM, or evidence of worn rings or other head/valve wear.

What I have not done: When cranking w/out the coil hooked up,the car sounds like cylinder compression is even, but I have not checked actual numbers. I am not sure that a small head gasket leak would show up in that kind of crude check anyway. I have not changed plug wires.

Any additional forum thoughts on this? It's driving me nuts,and my wife really wants me to focus on finishing our deck vs messing with this an old car. I'm too OCD to let it go, so before I either pull the heads myself, or take this to a mechanic and let him deal with it, I'm looking for any ideas to help narrow my options down

If this looks familiar, I started the same thread just before the forum upgrade,and my thread disappeared - right as I started troubleshooting, so that was frustrating in and of itself.
I'm going a different direction with your issue; When "under load" the problem happens caught my attention. Visually and ohm check your plug wires, under load is when they many times cause problems. My recommendation is to replace them if any doubts at all, cheap and easy regardless.
 
Joined
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Location
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My Car
1972 Grabber Blue Mach One 351 Q code orig 4 speed. Now: 427C Titus
I'm trying this one again now that the dust seems to have settled with the forum upgrade.

I'm fishing for ideas and feedback on the problem described below. About 2 weeks ago, I started noticing a drop in power cruising on the highway - it manifested as I slowly accelerated to pass traffic in a 4-lane highway. RPM dropped to around 2500, it felt almost like I was running out of gas, then recovered after a few seconds.

It seems to be load related. I can manually drop into 2nd, push the car up to around 4000 RPM or better, and if I hold that a bit, the same thing occurs.

I can run the car up to 3700-3900 RPM in park and it revs just fine. Take the car on the road accelerate to 3000-3200 in drive, and it wants to fall on its face.

I have gone over the fuel delivery from end to end. I swapped carbs with a spare, replaced all the old rubber (most of it was not really old, but it was cheap), replaced the stock pump with a stock replacement (only $20 and was not sure hold the pump was anyway), checked the hard lines, replaced the filter, and pulled the sending unit (it was clean, the PO had replaced both tank and sender a few years ago).

I tried a new coil, temporarily swapped in a replacement Pertronix module, and both checked/re-gapped my plugs to .035, then just for shits and giggles, replaced them (yes, checked the gap first). I made sure my timing did not change (I run around 14 degrees initial, all in @ 35/36 @ 2800). Vacuum adds about another 10-12 degrees,an have always run it off manifold vacuum.

I pulled the valve covers and did find some evidence that some valves are rotating as if insufficient seat pressure. I changed springs to a little stiffer set, seat pressures is close to 125 installed.

I road-tested after each change and found that nothing actually had any effect on the symptoms whatsoever.

Last night I realized I had not looked at the radiator fluid, and found it was a little low -I am not sure it's related, but now wondering if I have a small head gasket leak. The car has not overheated. There is no evidence of any coolant leaks, and oil level is normal. No evidence of oil/coolant mixing anywhere. If it is a leak, it has to be coolant leaking into a cylinder and small so it doesn't effect performance at low RPM (below 2500).

When putting a vac gauge on the motor, Idle vacuum holds steady at 16 Hg, which I think is to be expected with my cam profile, and I see no unusual behavior suggesting valve float when revving up to 3700 RPM, or evidence of worn rings or other head/valve wear.

What I have not done: When cranking w/out the coil hooked up,the car sounds like cylinder compression is even, but I have not checked actual numbers. I am not sure that a small head gasket leak would show up in that kind of crude check anyway. I have not changed plug wires.

Any additional forum thoughts on this? It's driving me nuts,and my wife really wants me to focus on finishing our deck vs messing with this an old car. I'm too OCD to let it go, so before I either pull the heads myself, or take this to a mechanic and let him deal with it, I'm looking for any ideas to help narrow my options down

If this looks familiar, I started the same thread just before the forum upgrade,and my thread disappeared - right as I started troubleshooting, so that was frustrating in and of itself.
I'm going a different direction with your issue; When "under load" the problem happens caught my attention. Visually and ohm check your plug wires, under load is when they many times cause problems. My recommendation is to replace them if any doubts at all, cheap and easy regardless.
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.
Curious to what happened with your lifters? I've suffered lifter issues also.
 

71coop

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I'm going a different direction with your issue; When "under load" the problem happens caught my attention. Visually and ohm check your plug wires, under load is when they many times cause problems. My recommendation is to replace them if any doubts at all, cheap and easy regardless.
The problem was the pinched fuel line - I confirmed that a good while back (this thread is about a year and a half old, not sure if you caught that). I did go over my ignition system before I finally figured this out, so definitely appreciate the input.
 

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