Mitch Johnson

Finally got the 83 928s back on the road after a considerable number of maintenance and repair jobs. Runs smooth in fact everything is improved except...I have no acceleration in 5th gear. I don't feel anything unusual with my uncalibrated assometer, all gauge indications are normal.

Just can't get it over 3k RPM but only in 5th....bizarre (to me)

For reference over the past few months I have done the following:

Installed solid Motor mounts
Installed solid alloy steering rack mounts
Silicone oil pan gasket
Installed oil pan stud kit
New Tie Rods
Replaced seals in PS pump
Replaced PS lines
Replaced PS reservoir
New alternator
New main engine harness
Timing Belt/WP/Porkensioner/Accessory belts
New timing gears, crank, cams, oil pump
Replaced oil pump seal, o-ring, and o-rings on bolts
Replaced clutch master cylinder
Replaced flexible line to clutch slave
New front sway bar bushings
Replaced gaskets on coolant crossover and oil separator
Replaced cam seals
Replaced front main seal
Replaced all coolant hoses
Replaced air filter
Replaced air pump filter
Changed coolant
Changed brake fluid
Replaced brake switches on master
New brake master reservoir
New coolant reservoir
New spark plugs/wires/distributor cap/rotor (gaps verified/adjusted)
Replaced distributor seal (on shaft)
New green wire
New vacuum check valve
New hood liner
New bearings for viscous fan
Added silicone oil to viscous fan
Replaced thermostat
Replaced temp sensors (temp/temp II/temp-time)
Changed oil/filter

Ignition timing ~7 BTDC at idle speed of ~750 RPM (can't find an idle spec only 23 BTDC @ 3000 RPM)

What did I screw up now?

Anyone recognize this symptom?

Jack Riffle

What I want to know, is where the hell can you even get it up to 3K in 5th gear............

Jim M.

Blocked exhaust from a bent or crushed pipe or cat plugged up???? Just a WAG.

Mitch Johnson

That is normally around 95-100 MPH for me, perhaps I am too bold, but there are a few highways around here that see that from me routinely.

Mitch Johnson

Yes, just what I thought, acts just like an exhaust restriction but only in 5th part has me

Bill Ball

What happens in 4th gear?

Andre Hedrick

What gear box do you have?

My OB w/ a G28/13 pulls redline 1-4, but 5th is tough to get much progress w/o a lot of road to wind it up.

Mitch Johnson

Runs like a raped ape...5K was as far as I pushed it, 1-4 were quite normal.

G28/08, this issue is something new, I've always been able to accelerate hard in 5th from ~70 and up.

SteveG

I had something similar, but I don't remember what it did in the other gears. Anyway, I found corrosion on one of the coil wire connections off the distributor. Check all inigiton wires??

Mitch Johnson

Ignition wires are new, I reseated them all just in case.

I can't help but wonder if it is a clutch issue? I didn't feel it slip at all but it does seem like I have lost some high end torque.

AO

Try putting the car in 5th from a dead stop. Release the clutch. If the car stalls immediately, it's not the clutch. If it slips... guess what... time for some clutch work.

dr bob

You'd see clutch slip in the tach-- car stops accellerating but the engine continues to speed up. If the engine brickwalls at 3k, it's not likely a clutch issue.

I tend to start at ignition components first, mostly because hey tend to deteriorate fastest. Then it's on to fuel system components. If you've replaced all the ignition bits from the coil wire through cap/rotor top plug wires to plugs, plus the green wire, you've nailed the likely pieces already.

Fuel system maintenance stuff includes fuel filter, and also includes fuel pump(s) and the suction screen inside the tank. My diagnostic methos would include a fuel pressure gauge, configured so you can see it at 3k under load in fifth. I would use metal connecting tubing brought to a gauge at the base of the windscreen. Plastic tubing is tempting but you really need to make sure that the plastic tube isn't going to melt on anything during your run. High-pressure FI hose and clamps would be OK too, short term. Just don't don't bring a pressurized fuel line into the cabin. You also have the option of getting a co-pilot to monitor a millivolt meter attached to the oxy sensor, as a first cut at finding a lean condition. The installed oxy sensor has a pretty narrow response band so it will just tell you if the car is way lean under your failure conditions.

Hopefully you'll get an indication of whether the fuel system is the root cause.

----

Set your timing at 3000RPM like the directions tell you. There are too many things pulling and pushing the timing around at idle conditions. Test at 3K and you'll have centrifugal advance pretty much all in. Much more reliable than at idle.

Mitch Johnson

Wow thanks, I'll get an external tach that can read up to 3k and time it right, the cheap one I have tops out at 1200.

Fuel system was next on my list of to do's, I've wondered about the state of the regulators and dampener at 25 years old and I'm sure the injectors could benefit from some attention, the hoses definitely have seen better days.

Screen in the tank sounds like nasty job, hope I don't have to go there.

I'll work on this and see what I find.

Much appreciated.

dr bob

Mitch, get a volunteer to sit in the Big Chair and hold 3k RPM's for you while you do the checking. I've been known to wedge things into throttle linkages then run around to look at the tach in the car to see where I wedged things. Takes a minute longer but lets you do things single-handed when needed. Running the engine unloaded at 3k RPM's won't hurt it.

Mitch Johnson

I'll try the throttle linkage wedge trick...thanks