koenig_roland

"offene Trichter" means the open throttle-bodies

Laker

Excellent stuff!

preston_brown

Thanks Koenig. Makes total sense of course.

When injectors get back and I get some readings off the AFR monitor hopefully we can start to diagnose the spitting through the throttle bodies and rough/non-existent low idle. Anyone have thoughts on the throttle return spring? Should I be crossposting to the racing forum?

preston_brown

I got the injectors back from WitchHunter and they were already in good shape. Good flow patterns even before cleaning, and after cleaning flow rates improved only marginally (3-5%). They were all flowing within the same range as well. So that wasn't the problem.

Worth a shot and eliminates them as a culprit though.

I got the injection system back together and put the "muffler" back on the car, but I didn't have time to start it today. Tomorrow I hope to get it started again and get some readings off the new wideband O2 sensor / AFR monitor.

preston_brown

OK, little update.

Car was started again with AFR monitor in place.

At idle (or what I can make it do to idle, i.e. hold it above 1k with my foot, and then even barely)....things are QUITE lean. We were seeing 16.5-17+. So no wonder there is popping back through the intakes and it doesn't want to run.

If you hold the gas and get it above 1.5k, then things smooth out and I saw the AFR come down to like 14. Blipping the throttle instantly richens things up and there is no problem with running lean on acceleration, either quickly up to 4k or so, or more smoothly.

So it really appears to be isolated to a problem down on the low end. Any suggestions on where we could proceed to diagnose what might be the issue? The stacks are all flowing evenly... is there a way with these throttle bodies to lower the amount of air at idle? I haven't been able to determine who is the manufacturer of the throttle bodies. There are large adjustment screws on each throttle body but I have a feeling they are for idle adjustment...i.e. manual stops for the butterflies. Would I be right with this assumption? There are other little vacuum ports at the base of each throttle body that appear to have a little piece of rubber coming away from them. On the left side one or two are hooked up to vacuum lines but the rest aren't. I assume they are plugged but maybe not. Do you think they could be the culprits?



I must go on the assumption the chip is a good map as it was made in 1997 and ran in lots of races.

Is it possible that there might be a problem with the Throttle Position Sensor (TPS) and it isn't sensing that the car is at idle, thus the idle fuel map is not being engaged? Is there a way to test this?

Any sense that the flywheel reference sensors might be involved?


Also, the air shocks work with 150 psi... I was surprised. The rears are quite spritely, the fronts a bit more lazy...surprised as I would assume the rear is heavier.

koenig_roland

Could it be a problem with fuel-pressure?

preston_brown

I don't think it's a fuel pressure problem. Injectors are all in tip top shape, and if fuel wasn't getting delivered by the pump properly, things wouldn't richen up and run better when throttle was applied (and when more fuel is required).

Dan Jacobs

Preston,
Have you checked fuel rail pressure? It's easy and you should so you have a baseline number.
I think I would also check the cam timing so you know they're both the same

preston_brown

I haven't checked fuel rail pressure, no. But I'm not sure why the symptoms I have described are pointing at fuel rail pressure or even cam timing... can you elaborate?

Jacke2c

Preston....if it were my car I would try disconnecting the throttle linkages that go to each bank of throttle bodies to insure that they are both allowed to fully close and return to their stops. That would be the first place I would look. Sometimes on multiple throttle linkages the shafts are sometimes removed, reinstalled and adjusted where there is inconsistency from side to side... shouldn't be, but it happens. I would also look at making sure all the potential vacuum leaks are resolved. It is cheap insurance to pull the throttle bodies and check the o-rings underneath and then to follow out all the vacuum lines. There should be a common vacuum manifold they should all feed to. Your earlier post leads me to believe that only a couple are used. Look at some other on-line sites such as Rothsport-racing.com (no affiliation...just a very big fan!!) and see under the EFI parts the vacuum manifold of which I speak. Any.. and I mean any leaks after the throttle plates will give you the symptoms you are describing....... By the way. If I hadn't nealry lost my leg from a motorcycle accident... I would say I would (nearly) give my right arm for that car... What a find!!!

FeralComprehension

I'm not sure that idle quality would be at the top of the priority list for race map calibrators. Seems possible that the high-flow injectors needed for high-speed WOT operation would be a little wonky at idle, and that possibly what you're seeing as an issue... isn't.

$0.02
FC

preston_brown

FC: we have considered that as a possibility. But you would think it would at least idle on its own without extra "help" from the pedal. Could be wrong...

evoderby

Hi Preston, I think you're asking the right sort of questions....I'm afraid that a methodical approach of eliminating possible causes is your only way of solving this.

Fact is the engine is getting too much air and/or too little fuel with the throttle at rest:

A)First thing I'd do is disengage the throttle cable and check whether no foot on the pedal actually brings the throttle mechanism at rest.
B)Check whether mapping is in fact pure alpha N (TPS x RPM) without additional idle circuitry
C)If the latter is the case check whether the TPS output is functioning correctly, usually around 0.5V at idle and 5V at WOT, if additional idle circuitry is present also check assorted sensors, valves and hoses.
D)Check for post throttle plate vacuum leaks
E) Check for injector and fuel pressure functioning up to spec. (checked!)
F) Only until all the above checks are made and crossed of the suspect list, there are two remaining causes;

1) ill-adjusted throttle plates. Check whether throttle plates can be closed up more at their rests, allowing less air to enter engine at idle leading to a richer idle. If so make sure to balance throttles afterwards at both idle and about 3500rpm.

2) if throttles can't be closed up further to realistically restore AFR, no vacuum leaks exist etc. etc. then the only cause left is inappropriate mapping for idle conditions.

Good luck Sherlock! ;-)

evoderby

BTW If you try adjusting throttle plates or mapping straightaway without the checks mentioned earlier you might be eliminating symptoms rather than causes, which is why I deliberately left these as final pieces on the check list.

preston_brown

Evoderby: Agree with that checklist. Will be working on that this week.