928 at last

Hi,
OK, just finished the intake refresh, and I have issues. Any insight would be appreciated.
Car idles poorly, and feels like it's not firing on all eight (like a few of the people I work with).
Really rough up to about 2,000 rpm, and then smooths out and runs like it's supposed to (feels like it. no assometer check possible at this point)..
Will idle, but not happy.
Story so far....
Sensors replaced - knock, hall, cps, tps, temp, temp II. Intake pressurized and good. All electrical connections cleaned and checked. Same with the vacuum system.
Throttle position checked re the throttle body and seems to be good.
Interesting ...car wanted to start without the MAF installed while I was checking fuel delivery. I took this as a good sign.
Fuel pressure running solid +50 lbs. ...thankfully no leaks, TPS is apparently triggering when it should, both on and off idle.
Plug wire routing checked and double checked that the right cylinders are recieving the right pulse from the caps.
Plug wire connections checked and clicked in securely. Both ends.
Just in case there was a sticky injector, I gently tapped each while the car was running with no change in the idle or anything else.
Any thoughts about what the problem might be would be appreciated!
TIA,

OK, Had a bit of time tonight. Next attempt - Saturday.
Vacuum checked at idle - (Rough and low)
As you would expect, idle seems to increase when a vacuum line is disconnected.
Note: no fuel in vacuum lines to the reg or dampers.
front fuel damper - approx. 7.5 inches.
Flappy feed line - approx. 5 inches.
Air Pump bypass - same as front damper.
Carbon Cannister feed - zip at idle, up to 10 inches at rpm.
Hose connections to the MAF boot checked and look ok.
Fuel pressure at idle is 55 lbs. No drop off after 20 minutes after shut down.
WSM indicates idle pressure should be 47.86 lbs and no less than 43.51 psi after 20 min. so we're a little high here, but not all that much.
Rough low surging idle, will stall if throttle applied after idling for a few minutes. requires about half throttle to restart. Engine smooths out at higher revs.
Seems like there's a massive flat spot coming off idle.
TPS rechecked and seems operational.
Wires and connectors gone over and seem to be good.
Ground point at rear passenger side was cleaned as part of the refresh.
Jump connection checked and cleaned too along with the connector and the ground line to the front lift point.
Next will be to check all the throttle linkage connections and adjust as necessary.
All input really appreciated.

928 at last

And as a footnote, the ISV is new, and tested fine on the bench.

jpitman2

Any gas smell out the back? Is 50psi normal pressure - my experience of LH is low 40s with throttle open, mid 30s at idle, but I may be out of date.
jp 83 Euro S AT 52k

928 at last

As far as I can tell, there's no issues with the fuel delivery system. No fuel smells anywhere. I've read that for my MY, 50 + lbs. of pressure at the rail is normal.

Jim M.

My guess would be a vacuum leak, but check all of the electrical connections, not just the plug wires.

928 at last

Thanks Jim,
Any prime suspects though?

Jascd

Please don't take this the wrong way, but did you hook all the vacuum lines up right? I just did my intake and I know how easy it is to get them mixed up. If you have not rechecked these then do it just to rule it out. I guess if you can reach it, check that the connector to the ISV is on nice and snug as well and did not come loose as you were getting the intake settled down. Make sure the MAF is on tight- basically all the easy stuff before you decide to lift the intake again...

Tails

Rob,

Do you have access to a diagnostic tester, Bosch Hammer, JDS Spanner or Theo's DT928?

If so have you run a diagnostic check on the car, LH, EZK, stored faults, input signals, actual values, idle stablizer, MAF values. RPM, O2 sensor, throttle full open and shut, and finally and adaotation set up?

If necessary take car for a run and see what faults occur.

Have you done a throttle, cruise control and auto gear box etc., mechanical set up as per WSM?

Have you done a vacuum leak test and double checked all vacuum connection are connected correctly. Especially vacuum connection to inlet manifold?

Have you done a inlet pressure test to check for leaks? Have you double checked all hose connections thta they are tight?

With regards to the injectors, have you used a noid light to check for signals to injectors and a stethoscope to check their operation (opening and closing solenoid valve). Personally not in favour of knocking injectors. Have you had the injectors cleaned, checked and fuel calibrated with no leakage?

Tails 1990 928S4 Auto

mcholdfast

I used the smoke test to find a vacuum leak after an intake refresh on the 89 GT. It turned out to be the intake gasket on the passenger side rear wasn't seated properly. Got a cheap cigar? The smell goes away after a few miles on the road.

SeanR

Un-metered air getting in the intake would be my guess. Lots of hoses/vac lines that can pop off during installation. Check the plastic Y pieces on each side of the MAF boot.

SQLGuy

50PSI sounds high to me as well. Maybe a bad fuel pressure regulator? If the pressure is too high you're going to get either too much fuel (easy flood, too rich) or, if it's REALLY high, injectors not opening at all.

928 at last

Bump

928 at last

Thanks!
Responses in Red .

928 at last

If it is unmetered air, I'll be *&^$&^#ed if I can figure out where it's getting in.

928 at last

I smoke cheap cigars anyway so that's the least of my worries...