figgen

Driving home tonight i had a chance to open her up and noted a few things:

85 5 speed,
Pulls hard in 1,2,3, skip 4 (BAD syncros) and go from 6,000 rpm 3rd to 5th and carry on, get up to 3,000 rpm in 5th (approx 120 or so…theoretically speaking of course) and car stops pulling. I take a look down at the ARM1 and RED...LEAN....RED....so I back off.

At Idle the ARM1 hunts in the middle
In 1,2,3 anything over 3,000 rpm is hard rich ( BLUE/GREEN), otherwise middle

Except in 5th.where I start middle to rich and go lean as I climb up the rpm to the point of 3,000 and no further.

Now the history

New fuel pump (my car only has the external one) September 2003
Fuel injectors cleaned and balanced Feb 2003
Fuel pressure diaphragm new July 2004
Fuel pressure regulator new July 2004
Fuel pressure regulator new July 2004
Fuel Filter new July 2004

So most of the fuel delivery system is new or re-furbished in the last 2 years.

SO...........why is my car doing this?????

Possible culprets??

Daniel Dudley

Clogged screen in tank ?

Garth S

You clearly have adequate fuel to reach redline in the lower gears, and the WOT enrichment switch is operating correctly. Theri is no immediate reason that suggests to me you have a defficiency in the fuel circuit that would comprimise redline in 4th or 5th..
If the fuel is unburned, it will read false lean .... and no correction ( impossible anyway) as the O2 sensor input is blocked by the WOT switch.
As the vehicle speed increases, more hp is consumed to sustain steady state - and more so when accelerating: this places the maximum load on the ignition circuit, and it could not be up to the demand.
I'd start with a simple cleaning of the rotor buttons and cap contacts, do an ohms check on all 10 leads, plugs & gap,etc - if not already done.

figgen

I'll give the ignition system a run down with the multimeter

History on my ignition system:
Coils - new 4 years ago
wires - new 2 years ago
Plugs - new 2 years ago
Distributor caps - new 2 years ago

They only part that has not been replaced (the others mostly on spec due to age) are the 2 black boxes on the leading edge of the front bumper in front of the rad (ignition control ?)

Thanks for the ideas!

goodspeed928

I have the same probem
check the f.t.p.s.

figgen

FTPS ???

Vlocity

Can you rig a fuel pressure gauge so that you can monitor the fuel pressure at WOT.

I wouldn't recommend putting it in the cockpit with you , but possibly you could rig a guage out the end of the fuel rail with some high pressure fuel hose and see if the pressure is dropping off.

When you saw the lean condition did the motor feel like it was down on power?

You do have the O2 sensor in the stock location before the Cats correct? An installation after the cats would drop your reading by a couple of points.

Regards,

Ken

figgen

I'll need to get a gauge that fits on the fuel rail.

The car was definitely down on power at full lean, It would not accelerate beyond the 3,000 rpm mark.

I have no cats (custom delete) but I do have an O2 bung welded in a cross pipe where the cats used to be. The O2 sensor seems to be working well during the other stages, hunting at idle, full rich at > 3000 rpm in other gears ect. It was new about 4-5 years ago ( but I only am able to drive 7 months a year too!)

figgen

Goodspeed - just searched on your posts...sounds like the same problem!

So my plan of attack
1) Check the resistance on ignition and plugs as per Garth
(what a pain on the '85...have to remove the big ol air plenum)
I'll have to search on the proper resistance values for each component (unless someone has them handy

2) hook up a fuel pressure gauge on the rail and see what's going on.
A good source for this would be ?????


3) clean out fuel tank suction screen
????? not sure if I should go here or not ????? I'd LIKE to do it just to say i've checked it but am a bit worried about breaking something that would require a fix. It would be nice to rod the screen out for full flow and put an in-line prior to the pump that could be checked or changed.

4) I guess I could always just drive < 120..........NOPE gotta get this thing fixed!

Jim bailey - 928 International

At 3,000 rpm your engine only makes about 150 HP so at 120 mph it probably needs MORE than 150 hp to accelerate ....the aerodynamic drag becomes huge. In the lower gears you quickly pass the 3,000 rpm range if in fact you ever get that low! What you were doing was much like trying to pull up a long grade in 5th at low RPM you open the butterfly completely but it just will not pull the hill. Which is why God created 4th gear so you could down shift , make more horsepower and use the torque multiplication of lower gears.

figgen

Your right Jim

In the lower gears WOT to the shift rarely gets me below 3,000 rpm. Your conclusion make sense, below xx speed drag is less so I can accelerate, once the drag = hp rating no more acceleration.


I'd buy that...especially given the relatively new state of most the items of possible concern on my car...so fix the darn syncros and get on with it.....

I'd still like to mount a fuel pressure gauge on a tapped rail cap. Do you sell those??

Garth S

Jim, Good call - I'd assumed that 3000 rpm was near enough the torque peak to pull on through .... wrong! So, a HP limited stall and leaned out by holding the foot to the floor ...
Rich - if you are ( insert adjective) enough , a long downhill run should get you past the 'stall' point in 5th @ 3000 rpm; however, adding 4th may be more viable.

jyoon

in 5th gear at 3000 rpm you are at 120? that seems way too tall. 5th gear should be drag limited close to top speed and that should be around 150ish and 6000 rpm shouldn't it? i'll go out in my 5 spd mazda start in 1st, 2nd, skip to 5th and i still think i will be able to reach top speed.

Jim bailey - 928 International

Jyoon the 2:20 gearbox is capable of 209 plus MPH just ask Marc Thomas 5th gear is really more of an overdrive for most people.

jyoon

i have a hard time believing 5th is that tall. at that rate, you'd be close to 240 at redline. cruising on the highway in 5th you're gonna be around 1500rpm. if it is truly that tall, i'll buy your argument jim, but sorry, i just can't believe it would be designed like that on purpose.