rcrone928

I tried to find info about why my 83 Ljet 928 US seems to run out of poop at about 5k rpm. When I START OFF from dead stop it'l shift from 1st to 2nd @ 4.5 k even if I keep the shifter in the two position. I can hold second gear to 5k but the engine just seems to be stuck around 5k and no more! Guess I'll never see red line in this thing. Was wondering if a 30 year old cat may be restricting reaching higher rpm or, maybe thst's all she's got....

brutus

The USA 4.7 does not much like RPM. Horsepower is dropping off and wind resistance increasing geometrically. You got about 200 hp at the rear wheels it is no rocketship.

Andre Hedrick

Strange as MY 81 fades near red line and goes soft when approaching 7K. She will easily go red line 1,2,3,4 but never tried nor would I expect RL in 5th.

IcemanG17

something clearly is wrong.......

When we first built the "lemons" racer (avatar..1984 L jet racer automatic) it would hold shifts WAY too high.....about 6500rpm...which is why the engine blew up....

however your shift points are far too low.....without more information, its hard to tell why it won't rev past 5k.....my best guess is a clogged fuel filter....or really bad plugs-wires-rotor-dist....

When was the last time it had a full tune up.....and when was the timing belt done last...

fbarnhill

Well, my old 83s 5spd kept pushing as far as I was willing to push it which was every weekend. I had a 5 mile run laid out with no traffic and no others... The reason I bought it in the first place (it already had 170k) was that it was much faster than my then new Mustang 5.0. I was only going to test drive it to have a shark under me again. I missed my old 79. I had my son with me and had told him there was no way I was going to buy a 170k mile car. That was one hell of a test drive. I drove that car for 9 years as a DD 70mil round trip commute. Only broke once when the aluminum ball joint broke while backing out of my parking space at lunch.
I had a good skilled mechanic. He did something with a flap actuator on the MAF. He said something about them getting hard over time. After that adjustment, the car was just awsome. Another thing he did that had just about as large an impact was rear wheel bearings. I didn't even know I needed them. They weren't making any noise but man were they robbing the power. However, the Auto boxes are a whole new game. I am on my 3rd now 86.5 and it is pretty good but not as nice as my 88 was. Though, I am still working getting it better.

Imo000

GEOMETRICALLY?

Dave928S

My first thought was fuel starvation ... clogged fuel filter or strainer, failing pump, etc.... (assuming it runs OK up to 5K)

If it's ignition, or ignition and fuel issues, I'd be expecting you'd have poor performance down low and under load as well, and not just drop off at the top.

rcrone928

well.. new plugs and wires and it really pulls hard to 5k but just kinda runs out of steam. I've never replaced the fuel filter and timing is spot on belt wise. Engine is running very well otherwise. It gets to 5k quickly and seems to have good low end torque. Thats why I THOUGHT about the cat converter. Will order new fuel filter as it may need that anyway. I also live AT five thousand feet altitude. Thanks.
a bunch

IcemanG17

change the fuel filter ASAP......

an ideal running 4.7L USA makes peak power at maybe 5000....probably a bit less with the stock exhaust...

With straight pipes and a single muffler out back my 84 made about 195whp-230 torque.....but it DIED after 5500rpm....

Just looked at my dyno sheets......its peak HP (203whp this run) was between 4500-5000 then dropped....it held "okay" till 5500 (about 185whp at 5500) then fell on its face....dropping to 165whp at 6000....

Peak torque was 241ftlbs at about 4000...strong between 3500 to 4500

Given you live at 5000 feet....your car might be just fine

rcrone928

Thanks ICEMAN. I guess I was just expecting a little bit more from a v8. The vaunted porsche motor and all. I shouda bought the 83 euro off craigs list when I had the chance.

Fogey1

Green wire? My '83 pulls fine to redline.

rcrone928

fogey1. Is your 83 a 5spd or auto? And why would the green wire affect top rpm?

anonymousagain

You should be reaching redline, just slower revs past ~5500rpm and with thinner air. Will it eventually get there? or simply stop revving and hold at 5k in 2nd?

Fuel filter is a must.
Green wire is the Aorta to timing for L-jet...although it seems green wire symptoms would be more cutting out, but I have no expertise with this.

Fogey1

Sorry. It's a five speed.

Degraded signal quality through the green wire could change the efficiency of the ignition. Analogous to burned or de- or over-gapped points on an old-fashioned ignition system.

In some of my prior lives I spent time kneeling behind VW's and Porsches, hovering over opened distributors with a Swiss Army knife in my hand.
http://www.swissknifeshop.com/shop/s...army-executive
Note the file, and the approximate Phillips and straight screwdriver ends.

Great tool. I've had one in my pocket for 55 years. Thanks, Dad.

(The scissors get a lot of use, too)

rcrone928

Ok I get the point about the green wire and the fuel filter. You guy make good points. What i think i'll do is go on a drive down to a lower altitude and see what happens. I did check the connector on the green wire and the plug broke into several pieces but the wires themselvs seem to be intact. As far as trying to rev past 5k I didn't keep it floored as it seems to be beating a dead horse. Also I was running out of clear road and didn't want to risk picking up a LEO. Now at least i have some things to check. As always you bunch have been alot of help. thanks again.