Troubleshooting: Engine lacks high speed performance/ power.

O K here's the problem: The engine starts out strong and sounds like a beast. After a short distance which varies from a few hundred yards to a few miles the engine starts to loose power and lacks high speed performance. It gets worse over time. When the problem occurs I have to give it more gas to maintain speed, which increases revs and makes a lot noise but doesn't translate into proportionate power at the wheels. Reducing speed increases engine performance slightly. If the problem occurs at a time where I can't easily reduce speed, such as on a highway, revs sound uncharacteristically high and I'm praying that I don't throw a rod, again.

Background: Ten years ago, I threw a rod going up a small hill and I had the engine rebuilt to stock specifications. I drove the engine very little for ten years. Two years ago I started working on this car and I found this site. The engine probably only has a few thousand miles on it so far. I've done a lot to the car in this time, but this problem remains. I now admit, I need help.

Known problems included: Cracked and loose exhaust manifold. Poor positive battery terminal cable. Leaky radiator. Fly wheel a quarter inch too forward. Noisy rear. Hot carburetor.

With the exception of the hot carburetor, I don't understand how any of these issues might be causing the problem described above, so I don't know where to go next.

I've done all the normal stuff. fluid changes, filters, and points, rotors, distributor cap.

I'm pretty good with the electrical stuff so I started troubleshooting here.

Upgrades: ignition uses TFI module or point (I can switch between them and problem occurs during modes) Blaster II coil. 7mm spiral core spark plug wires. Colder spark plugs, gapped at .040, indexed and pointed up. GM alternator swap. I'm running 15 Volts (w/ TFI), even when the problem occurs. I bypassed the carburetors de-icer.

I have long tube headers waiting to be installed, but I want to fix this problem first so I can feel the difference on the highway.

My experience is limited when it comes to carburetors, transmissions or internal engine parts.

It's a 67 mustang with original carburetor and distributor. I haven't done anything to the carburetor since I had the car inspected almost a year ago, except try different air/ fuel mixtures and then put it back.

After each upgrade I can feel an improvement at idle and while pulling out of the driveway, but my hopes of of fixing the big problem fade shortly there after. This is embarrassing when going up a hill at reduced speed and potentially dangerous when entering a highway on ramp. Can anyone point me in the right direction. What could cause this problem? Should I concentrate next on the carb, trans, headers or something else?

What transmission do you have. Your trouble may be there if its a slipping automatic.

It's a C4.

I'd bet a quarter that the fuel tank is full of crud and after driving a while, it plugs up the pickup sock in the tank, starving the engine for fuel.

Transmission does have delayed engagement. I've lived with the cluck for years. Admittedly, I once mistakenly put a few drops of engine oil in the trans dip stick. (Both black quarts look alike) I've dropped the trans pan three times this year, (for other reasons) displacing at least nine quarts of oil. I haven't noticed much change in problem before or since.

The fuel tank is eleven years old. It sat for those ten years with only an occasional use. Two years ago, I noticed a fuel leak. I started using a fuel storage, additive, to absorb any water. I never drained the tank on purpose, but lost good deal of fuel before fixing the leak last year. I've maybe gone through twenty tanks so far. Every four tanks I add a gallon of 100 octane low lead. I always fill the tank in order to tracking fuel millage. millage had decreased since I've started keeping track. MPG: 8, 10.6, 12.7, 13.2 14.4, 11.1, 9.5, 9.0, 8.9, 9.6, 8.1

Maybe do a compression check to see if the rings were broken in properly.

Fuel tank full of junk is my guess.

I had the same performance problem with my C4 before i swapped to a t5... it was right before i swapped.... what i did;

I ran the e-brake on a dyno test... ever since then the tranny really didn't like to accelerate even tho the engine loved to rev... i put it in nuetral while coasting with traffic and rev high then drop it back in gear to get more acceleration out of it... it didn't like to accelerate quickly but when i got up to speed (~45-55) it would fully engage and go, but at take off even granny was honking at me...

if this is what your car does try adding more trans fluid... the torque converter takes alot of fluid to engage properly, fill the tranny past the 'full' mark and see how that does... i had to go 1inch above the full mark on the dip stick for the tranny to engage properly...

Hope this helps,
Richard

edit; it seemed to accelerate better when i gave it less gas... lower revs but i would defently check the compresion on all cyl...

The car used to spudded while going up a hill, but that's not the problem I'm describing now. I can be driving on a level ground and I feel the car loose power at the wheels. I can rev the car just fine, with out feeling a choking sensation, which would be how I imagine a fuel shortage would feel like. Just the same if you know of a way to get rid of the junk at the bottom of my tank, I'll give it a try,

Are you suggesting a compression based on my problem or the age of my rebuilt engine. J/C. Either way, I'll do one next weekend. What's PSI am I looking for?

Richard, would your car have trouble regardless of being hot or cold? Mine trans level is about 1/4 over full. It makes me feel better that you say this is a good thing.

I mean 1/4 inch.

It sounds like the transmission is slipping. If the engine revs higher and the car goes slower = trans.

Oh yeah, my e-break is stretched and more or less useless. I don't know if its related. I never thought about it before. I'll try over filling the trans right now if you don't think it'll do any harm.

Anyone think the engine oil could be causing this, should I empty out the whole bell housing of trans oil. Please say no. Lol.

Maybe there is a bulb burned out?

don't empty any trans oil... you don't want less you should try more... to be honest i think a few times i have fill it past 1inch on my dip stick more than a few times for road trips..

i didn't have a problem when cold... like you said it wouldn't start until hot or parts were moving faster... not quite hot but getting there, up to a few miles aways... i knew my torque converter was slipping from the day i got the car... but trans fluid seemed a like quick fix every month for a year (oh how i have a learned so much) i'd deffently try the trans fluid first... if your fine on reving and it's not having a breathing issue in normal operation (mine is 600-4200rpm) then i think your right on not being a gas or compression problem... if the fluid helps it's a quick fix but i don't recomend going very long with it (traffic seems to still avoid my car even tho i'm now keeping up with them )


Richard

Axle Roads":2sys43s0 said:

....... I'll try over filling the trans right now if you don't think it'll do any harm.

Click to expand...

the only harm i can see is the puddle under the car... oh wait that's harming the pavement not your car....

Richard

i'm not sure so if i'm wrong some else correct me... i've ran with 1inch extra fluid in trans so i don't think it will hurt...

A burned out alternator indicator bulb might cause similar symptoms. Is that what you mean, Tony? I suspected the alternator regulator wasn't good enough and I've replacing most of the charging circuit. (except for the battery positive cable). The alternator, most of the wires, terminals and bulb are all new and clean. I've experienced the problem with a voltmeter tie-wrapped to my dash reading 15 volts at my main junction. I wish it was an electrical problem, but its likely something else.

Richard, do you mean that you had to add more trans fluid each month until you did the T-5 swap. Was that because of a leak, (just to keep it at 1 inch above normal) or do you mean you actually progressively raised the level of fluid in the pan each month. When I said empty out the bell housing, I mean replace with fresh fluid (All 15 qts). I don't have a tach to confirm rpm, but otherwise, sounds like you have an understanding of what's going on.

I found my compression tool and instructions. I'll do this sooner rather than latter.

i kept it at 1 inch... or above... not progressivly.. but i did have a leak, the problem is i couldn't find it... it looked to be everywhere... i'd clean it up and the next month it looked the same amonth ago so i jsut gave up on trying to locate the leak ... but i always kept the fluid 1inch above the 'full' line you can try it and drive around and see what that does....

another thing i just thought about.... try the vac advance module.... i have a 65 LOM distributor so my advance is dependant on the vacum... when my vac advance module was replaced it was night an day on acceleration.. (i forgot about this one).... to test your vac part take the hose from the carb and blow gently (don't suck unless you want a mouth full of fumes... ) you can do this with the car off.... if air excapes evenly or completly then you found your acceleration problem...

i can't think about anything else...

Richard

I just tried it. Got it up to 1 1/2 inches. Just like all the other things I've tried. It seems to make a difference at first to my uncalibrated butt-omeeter. But on my third time adding trans fluid and driving around the town it failed royally. Same issue, no doubt about it. When I got home my exhaust manifold was so hot it was glowing red. At night I can see sparks coming from cylinder number six. Somethings not right.

I know what your talking about with the vac advance module. Last year when I had the car inspected I asked the mechanic about it and I watched him blow into it. He said it was fine. Still, I added Teflon tape to the hose about nine months ago, witch IIR, seemed to make a difference too at the time. I've had the hose on and off since than and the tape doesn't last. I need some kind of plummer Teflon goop. Anyone know what that's called?

One more thing. Someone chime in here and tell me I'm wrong. If it was the vac advance mod. I would have a problem accelerating off the line. Thirty seconds after the problem occurred on that last trip I hit a red light. I sat there for maybe thirty seconds. On green, the car felt great off the line, I hit the gas I didn't notice the disconnect between the engine and the wheels until about 30 MPH.

If the exhaust manifold was glowing red wouldnt that indicate a lean condition?

Im not a expert but would seem to me that the carb and/or timing is messed up.

Does this car have one of those linked loadamatic distributors that require a specific carb?