Losing power

[Tonyakavw]

I have a 1975 1.8 engine (with original L-jet) in a 1973 body. Yeah, I know it sucks, but it could be worse... Anyway, I have been having a problem recently and I've narrowed it down to a few possiblities.

symptoms:
After driving on the freeway for a few minutes, and after I'm at cruising speed, (very little throttle) I lose power occasionally. Sometimes I am able to recover by using the momentum of the car to start up again by popping the clutch, but it doesn't seem to be a reliable method. Its as though the engine doesn't want to fire up for maybe 20 seonds or more, like there's some hysterisis keeping the engine stalled for a bit. This happened tonight for the first time at a stoplight. I was idling (at an already high 1200 -1500 or so) and all of a sudden it just dies.

So here are my theories...

1. Throttle position switch. I have read that old, worn TPSs can cause problems at high speed/low throttle, but the hysterisis in the stall makes me wonder if this is the problem..

2. Fuel pump. Another obvious culprit, but why would this only occur with low throttle? Also, being my daily driver, I have not had it stall on my commute (no freeways) basically ever... So this causes is suspect too... Could the fuel pump be the cause of the hysterisis?

3. Vacuum leak - Just because they are so common

4. Vapor lock


So any ideas as to what might be happening?

[Tonyakavw]

.

[rockaria]

I will take some stabs at it for you.

I have a nice 75 1.8 L-Jet that I have gotten to run fairly well (Never brag on a 914 or tomorrow... Who Knows!) But here are areas I have seen that could cause this phenomonom.

1) Ignition switch! - My bad ignition switch would work perfect when the car interior was cold, but failed once it heated up. Then like nothing, the contacts to the electrics failed and bammo, no spark or fuel pump. for $15 bucks its worth changing out... Does the radio go out when the car does its bad thing?

2) Main Wires. My main harnes wire was loose at the reg board, making intermitant contact. In fact when I went to fix it I noticed the Fuel pump wire on the startup completely off (No fuel when starting) Now that was a bugger.

3) FI Harness wires - "Freekin A" Are these easy to break in the harness. I have had my AAR Wire work, then not work, then work when I grabed the harness way down in the bay.

4) Resistor pack - These break easy as well. Though I think they break clean and would leave you starnded so possibly not them.

5) Bad fuel pump - or maybe a bad wire or ground to the fuel pump. Also check the fuel filter, blockages that can be messed with might do it.

6) Air box flapper sticking - This is comon if you have recently had a bad backfire and it warped the flap. Also on this point the FI harness connection to the Air Box may be lose or going.

I have not had trouble with my Throttle switch. It is a simple three plug (NON-Adjustable) switch. Last weekend I took it all out to adjust and to my surprise it was not adjustable.

Is that a good start? I would begin with the Ingnition switch. I spent tons of time fixing everything else till someone said "Hey dude! just look at it and see..."

Also, I have had vacuum leaks and unless thet were big it never shut down.

As well I live in the hot, hot desert southwest (110 for two months) and my 75 NEVER vaporlocked. The fuel pump is in the front in a cool area. My older 72 would vapor lock all the time, but never when running.

I hope this helps!

[74914]

5) Bad fuel pump - or maybe a bad wire or ground to the fuel pump. Also check the fuel filter, blockages that can be messed with might do it.

Years ago I had rust in my tank that caused similar symptoms. While driving, when it would start to bog or die, I could clear it by yanking the wheel back and forth to unblock. I could also "stir" it out of the way with a long thin rod. I could feel the mush through the rod. Then I bought a rust free tank.
Ed

[Jake Raby]

clogged fuel filter, or something with fuel delivery for sure.

[Tonyakavw]

Thanks, these are all very helpful hints. After some more driving I am increasingly inclined to believe that there is some temperature dependency here. After driving on side streets for 30 minutes or so, I experienced the same effect. The previous owner had placed the fuel pump in the engine compartment essentially on the right side of the car where the trunk light is on the drivers side. So maybe it is a vapor lock problem... However this has all happened during relatively cold weather, so its not clear to me.

-Tony

[gint]

I had a Spitfire once that would only run for 5 minutes and then quit. I thought at the time that it must be a heat related problem. After a week of troubleshooting (thinking it was the fuel pump for quite awhile), I finally pulled the hose from the pickup tube in the tank and placed it in a 5 gallon gas can and drove the car for 15 minutes. It didn't ever quit while running this way. It turned out to be a 1" plug of rust (formed from loose particles) that had formed in the bottom of the fuel tank pick up tube.

[Mike D.]

Someone earlier mentioned checking the gas tank. I also worked on a car, with similar symptoms that had rust chips in the gas tank. It is a quick easy check too. Get one of those magnets on the long telescoping stick (looks like a car antena), and stick it down in the tank, move it around the pick up screen and slowly pull it out and check for rust. If none then move on to the next thing.
Good Luck,
Mike D.

[JohnB]

I've been having the same problem lately and also think it's wx dependent. Been cool here in the DC area recently. Never had this problem on warm days.

Car starts fine, 2-3 minutes later it wants to quit completely and other symptoms Tonya described. Battery/alt is fine, my guess is fuel pump/fuel line related. After getting the car to restart and nursing it through the hiccups it runs perfectly.

It's the kinda thing that costs a fortune to identify and 20c to fix, I'll just betcha.