Jim H.

Hey guys,

I'm new to this board. I just installed the Guru racing chipset for my 89 951 with a few modifications (extrude honed intake, B&B Catless exhaust, Carillo rods) but mostly stock (turbo, IC etc). In any event I just started the car up after installing the reliaboost, the 3 bar FPR, and the chips. Now when I come off the gas the rpms decline but hang up around 2k rpm and then slowly fall to around 1000. Any ideas?

Thanks,

Jim Huizenga

RJP 951

Jim, sounds unrelated to the changes you made, and more like a TPS that isn't closing (or not consistently).

Ron

turbite

Yeah, I second that, sounds a lot like the TPS

Jim H.

Thanks,

I'll look into the TPS. Cool thing was I got ahold of Danno today (Sunday) and we talked about it. Decided to take it for a drive and see how it behaved after it was warmed up. Worked much better with just a slight slow in rpm decel passing through 2K. I'm really not sure if it didn't always do that. Currently it is essentially behaving normally but pulls much harder earlier and with partial throttle. Didn't feel like the top end was improved much over the APE II chips though. Since I mainly wanted them for increased driveability and safety (no lean condition on top) I'm very happy. We'll see how it does with cold start tomorrow morning.

Thanks again for the replies.

Jim H.

sm

Maybe this will help:

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=18;t=005463#000000" target="_blank">Thread about the slow rpm drop</a>

Danno

Hi Jim,

Looks like I need to lean out the mid-range slightly on the TurboS cars as they have more lag and less flow than the non-S cars. That's the hesitation you get around 2k (too rich).

"Now when I come off the gas the rpms decline but hang up around 2k rpm and then slowly fall to around 1000. Any ideas?"

As for idle-speeds, check the TPS where pins #4 & 6 should be connected with the throttle closed. When the throttle is opened, they are disconnected. However, this just selects the idle vs. partial-throttle fuel-maps, which doesn't really affect engine-speed.

That is more a function of air-flow. If you have too much air entering the engine, it will tend to have a lazy drop to idle. This may be due to the throttle-stop being too open or a vacuum leak in the hoses under the manifold. The chips are only an after-the-fact component that only responds to air-flow.

The other thing that sounds suspect is the idle-stabilizer. Try screwing in the idle-bypass screw on top of your throttle-body by 1-2 turns and see if the idle drops quicker. If it drops to 700rpm and picks back up, you went too far, so split the difference.

Jim H.

Thanks for all of the excellent input. Tomorrow I'm going to dyno the car (Mustang Dyno) and get an A/F plot and a boost plot with the HP and TQ curves (I'm expecting the HP numbers to read low per Mustang standards but it is really the A/F and boost I'm looking for). Danno has already agreed to look at the curves and remap a new chip if that's the problem. If not then I guess I'm going fishing for a vacuum leak or something. I will let you all know what happens tomorrow. Also, if I can get the dyno curves digitized...anyone interested in helping me post them (I have no clue how to do this).

Jim H.

nickhance

I've got this same problem. I just installed my GURU chips after a fresh rebuild and it will occasionally idle around 2k then come down to 1000. (Usually if I blip the throttle.)

It was the TPS at first, as I didn't have enough slack in the cable and when the engine heated, it expanded and pulled the cable off idle. I've fixed that.

The ISV should be clean, I cleaned it back in December and I'm pretty sure that's the only time it's been cleaned since the car was new (wasn't too dirty, but enough that it needed a cleaning.)

This seems to be the same problem, but I'll try the things mentioned here to see if they make a difference.

adrial

Jim H,
If you email me the dyno plots I'd be more than happy to post them.

--adrial

Jim H.

DynoJet Dyno numbers:

Max RWHP = 286.5
Max RWTQ = 338.2

A/F looks good to me but waiting on Danno's advice.

Adrial - You've got mail. Thanks for helping post the graphs.

Jim H.

Waterguy

Holy Hanna, those are nice numbers. Close to the typical 300 rwhp "barrier." A typical 89 951 running only chips and Reliaboost at 15 psi will pull about 260 rwhp/290 ft-lbs rwtq. The work done on your car is really helping your breathing and numbers. How are you measuring boost?

Srock Guru chips might not work for your car, as it is not behaving like stock. Other concerns would be pinning the AFM (not measuring the actual air flow) and possibly maxing out the stock injectors (they are good for about 300 rwhp at 100% duty cycle.)

You are definitely doing the right thing measuring the A/F on the dyno and going for custom chips.

Danno

Here's the chart that Jim got:

<img src="http://www.gururacing.net/CustomerCars/Dyno-JimH-TurboS030617.jpg" alt=" - " />

I would say that the limiting factor here is the stock-injectors. It's possible to drive the TurboS turbo to higher-boost than this 15psi, but you'll end up with the rising and lean air-fuel curve in the upper-RPMs as the injectors run out of fuel.

Also the rapidly dropping torque-curve can use some help with flow-increasing mods in the upper-RPMs.

adrial

Jim, email? No I don't...

holy $hit those are some nice numbers...

Danno, at my dyno day on the 28th there will be my car running Steve R and another car running Guru...both 89 turbo's. The only difference being that my car has a test pipe.

It'll be a head to head comparison of the 2 best chips on the market IMO...

I agree A/F looks pretty good above 4200rpm...below that...I'm not sure. I believe the a/f's are so high because the car is going from open loop to closed loop, but I think that happened way earlier on my car...this may be pointing to an AFM adjustment...

Don, how much power did your car lay down with guru chips?

EDIT:
Here's an a/f chart from my car when it was bone stock, making 11.9 psi of boost with stock boost control.

<img src="http://members.rennlist.com/adrial/dynoAF.jpg" alt=" - " />

Waterguy

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> Don, how much power did your car lay down with guru chips?
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I don't have Guru chips yet; they need to be my next investment. I dyno'd 237 rwhp/244 rwtq on my unknown aftermarket chips, and was very rich throughout my curve, rising to 12.5:1 at 6400 rpm.

Jason_86_951 had Guru chips, and dyno'd 255 rwhp/290 rwtq iirc. The torque numbers were very good, but his horsepower was not alot better. This may be due to his smaller turbo, or the fact that my A/F curve improved near the HP peak.

We dyno'd three other 951 cars with the KKK26-8 setup and aftermarket chips. I don't have the curves, but I think they generally pulled about 260 rwhp, 300 rwtq. Mine was by far the underperformer of the 26-8 turbo cars. No really modified 951s at the dyno day this year.

Jason_86_951

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> Jason_86_951 had Guru chips, and dyno'd 255 rwhp/290 rwtq iirc. .[/QB]</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">240 RWHP / 280 RWTQ
For now anyways.............