Fuel Pressure

[Frank Schwartz]

Took my 73 Mk iii W/440 out for a 150 mile run today. Some hesitation in acceleration occasionally and idle is not consistent.

I have an Edelbrock 1411 carburetor with Edelbrock manifold. All has been well until last year when it began to idle strangely. Took the carburetor apart and cleaned it well and all was fine. But not today.

I also have a pressure gauge on the fuel input line to the carburetor and it reads only 3.5 psi. I thought it should be more. I also have an electric pump in parallel with the mechanical pump which is used to prime the carburetor and shuts off when the oil pressure starts to rise.

I am beginning to think, before I tear into things, that perhaps the fuse to the electric pump may be bad and the electric pump is not working at all....and that the mechanical pump on the block may be ready to fail.

Can anyone tell me what the actual correct psi to the carburetor from the pump should be???

Thanks
Frank Schwartz
73 Int. MKIII 140/5975
in Hendersonville, TN USA

[Lee Grover]

Hi Frank,

I had a fuel pressure gauge on mine awhile back,at the input to the carb. F series 383 w/Holley 4160 on the stock MOPAR manifold,stock mechanical pump. I would see up to 6psi while the bowls filled,might have had that reading under load also. After the bowls filled the gauge would read between 4.5 to 5 psi at 800 rpm idle. Can you hear the electric pump ticking? Every one I'm familiar with makes some noise. Check the filter too,might have fueled up with some bad gas.

My son lives in Hendersonville,told me he's seen an Interceptor driving around the area. He drives a blacked out Mercedes AMG sedan,a few years older.....just in case you get a thumbs up and a wave from one

Lee

[Frank Schwartz]

Lee:
If your son saw an Interceptor in Hendersonville, that is me !! I think the problem may be more than I thought. Seems the voltage is fluctuating and I suspect a bad ground, most likely from the battery..although I have a replacement alternator to put in as I had a problem like this about four years ago with a heat sensitive alternator...right now it is 90 degrees and I will wait until early morning or so when it cools off enough to do some outside work...

The engine was missking on occasion and it took forever to find the heat sensitive problem..but now I think I'll check the integrity of all major electrical posts and then go from there.

I'll report.

And, Lee, if your son is into Jensens, why not have him drop by sometimes and see the cars and talk shop..

Frank

[Lee Grover]

Thanks Frank,I'll pass the invitation along. He was raised to be a lifelong gearhead Currently working at a marina on a nearby lake. You have a cooldown headed your way,dropped down to the low 80s here,from 100. Have you checked the levels in the battery cells ? My battery tends to get thirsty when the ambient temp gets up in that range.

Lee

[Frank Schwartz]

At the moment, I am suspecting either a bad ground , possible battery (new last year) but mainly the alternator...voltage is usually 14 on start up but goes to 13 or less now while running. Have a GM 100 Amp alternator in it which requires a resistor and light bulb from 12v for exitation and the light goes out when the alternator is running. Now it is on all the time, which tells me it is definitely an electrical problem...but have to wait for a bit cooler to work on it. I have a VDO oil pressure gauge (electrical) and I noticed it jumped a bit and the engine burped a few times under initial acceleration...all of which I THINK is electrical... Oddly I got terrible mileage on the 150 mile run this past weekend with the Nashville British Car Club rally...and wonder if my problem could have caused such rotten mileage...never had that before..usually 14.5 mpg always...

The GM rebuilt alternator came from AutoZone and has a lifetime warranty, so if I replace it, I only have my time involved. Originally I had a similar alternator from K&D that did not require the exitation voltage..and it went bad. I found this GM unit..exactly the same but required the voltage and have had it in there for four years without a single problem. The original K&D 100 amp alternator went bad and turned out to be heat sensitive, so I used this same unit with the voltage exception. Then found a local shop that rebuilt the old unit and replaced the heat sensitive items..... I carry it as a spare, but since AutoZone completely warranties the unit, I just picked up another..no cost... So...in a week or so I should have the answers...

Tell your son, he will be most welcome to come over and kick tires etc. Son, Mark, is here on weekends so he should come then and visit. Call first at 615-824-5467

Regards to all... and if anyone else has suggestions and/or comments, they are welcome..

Frank Schwartz

[Frank Schwartz]

Forgot to say that I have not checked battery fluid. I did have the battery and alternator "checked" at the parts store and they said all was ok...but it is not...so we go from that...and will see soon.
Frank

[slotcarone]

Hi Frank
Did you check for a proper ground going from the battery to the engine? Also make sure there is a ground to the frame somewhere. Please keep in mind the Autozone store workers are not mechanics and rarely know anything about cars! They can put the alternator on their testing machine but usually do not know how to use it. Sounds to me like all of your current problems are related!

[Frank Schwartz]

Plan to check all this weekend..will post results
Frank

[Frank Schwartz]

Two problems...One..the alternator was bad...replaced with new manufacture (GM style 100Amps) and now voltage rides at 14 at idle.
Found distributor cap and rotor also badly in need of replacemnt. Starts immediately and run smoothly...not road tested yet, but in the next few days...so all seems to be well in Jensenville.

Frank Schwartsz

[Frank Schwartz]

Strange things...often what one thinks is a particular problem on a car, turns out to be something else. First, the alternator was bad and I have replaced it with a new one....but the major problem, after I went through the carburetor and found nothing...was...the rotor and distributor cap !!! It seems, the spring on top of the rotor had broken in half and the spark was still going from the inside of the center electrode on the cap...and it seems that the spark must have jumped three times before it got to the spark plug itself...no wonder I was getting poor mileage and hesitation and such. A new cap and rotor seems to have solved the problem. Why and how the spring broke in two on the rotor top is beyond me. I found the broken half inside the distributor just lying quietly there. It was only on a hunch that I decided to even look at the distributor cap and rotor.......

How long this problem existed, is beyond me. Why and how that top spring broke and literally destroyed the inside of the cap is also a mystery...but even so, the car would still start and run...which is amazing to me.......

Starts are instant now..and I'll have a chance to give it long road travel test in about two weeks...

Regards to all,

Frank Schwartz