Well, after getting my car dyno'ed, I now need some help fixing some problems I found.

I made 224 horsepower and 336ft-lbs of torque. Thats with my A/F ratio at 10.2 at 4100RPMS.

1.) The tach reads 6000RPMS and the fuel cuts off (rev limiter, but apparently I have a aftermarket chip cause the L98's aren't limited until like 9900RPMS). What can I do to fix the tach problem? I've heard of a filter or something, but don't understand what to get or find.

2.) How do I get my motor to run more lean? I am running 10.2 at WOT with stock injectors, FPR, and fuel pump. I heard of possibly running lean, but don't know how to correct a rich condition when everything is stock. However, at idle, it is running maybe 16-17 on the A/F ratio. Any help?

3.) How much power could I be loosing if it only revs to 4100RPMS and has a A/F ratio of 10.2:1?

4.) With that power, I still can't spin the tires, much less chirp them. Any new ideas?

Thanks!

-Dave

 

Anyone?

 

...maybe be a tad more specific in your title to attract the right type of tech person?

 

have a question of my own...why is he putting out 224 when the stock car is supposed to be 230+??

 

Well all this is a bit difficult to understand but I'll take a shot. I'll number my responses to your numbered questions/comments.

#1 Tach problems should have nothing to do with performance. Usually new filter doesn't fix tach. I had to buy a reconditioned cluster from GM to fix my 90 tach. I'm not sure about your chip/rev limiter situation
#2 Have injectors checked for any sticking open. A sticking injector or two will cause a rich condition but will usually throw a code 45. You will have to listen for pauses in the steady ticking of injectors with a mechanics stethoscope to detect as just checking ecm pulse will not reveal. If ok, then install an adjustable fuel pressure regulator and drop pressure until satisfied with leaness.
#3 not sure about air fuel ratio.
#4 1990 L98 should be around 245rwhp stock. In 1990 the L98 no longer used a mass air flow sensor but went to speed density and the higher compression ratio and new cam added 5 rwhp over previous years 140rwhp.

I'm guessing you may have a clogged cat or other exhaust issues just off the top of my head resulting in that hp loss.

Also, are you getting any codes??

I hope I've helped a bit, but if nothing more, it's a thread bump.

 

Stock CHP was/is 245. With an auto you would have ~17% drivetrain loss which would work out to 203 RWHP. Less loss with a manual. I'd say he has a few mods.

 

1) Are you sure you have a fuel cut off?
Tach reading has nothing to do with the real rpm reported by the ECM.
If you are able to do a scan you will see the "real rpm level".
In any case I think is stupid to cut the fuel with a New burned chip to only 4100! the problem should be elsewhere . My 90 has the same tach problem (all 90 are the same) and I have an aftermarcket tach. (when I'm at 5000 rpm the stock tach says 6500!)
2) How yoou can say you are 10.2:1 at WOT?
Unless you have a Wide Band O2 sensor you can say you are at 10.2:1 AFR.
If you are referring to a datalog from ALDL, 10.2:1 is common because is the stock AFR that the ECM commands via chip. There are tables (when in PE = Power enrichment) that allow the engine to go to a Theoretical 10:1 AFR. (I said theoretical AFR because is based on the stock Narrow Band O2 sensor)
My datalogs are full of 10:1 AFR at WOT but I bet if i hook a WB O2 sensor the real AFR will be close to 12.5:1.
The only way to lean a calibration is to go deep in the chip. But As I said I bet this is not your case. (= read you are not rich as you think, Not 10.2:1 AFR).
If your reading of 10.2:1 is from a WB o2 reding, Yes you are definitively too reach and you have to go modify the tables reganding PE, leaning the calibration. (I can explain here how to ..too long)
3) If you are really only at 4100 and 10.2:1 AFR you are loosing at least 20 to 25 Hp..... but since 224 horsepower and 336ft-lbs of torque (If RWHP) are very high numbers for a stock 90 L98 it seems you are NOT loosing HP and torque.
4) I think your dyno nubers are not real. With 224 horsepower and 336ft-lbs of torque (!) you should be able to loose traction even with a 2.59.
-Beppe-

 

The mods I have are flowmaster cat back system, K&N filter and cut lid, tossed frisbee, bored .040 over motor (with stock CR, cam specs, etc.) and some light porting of the plenum (but not the runners or base.)

Ok, let me try to help you guys out. The chip is stock, I just checked. However, on the dyno, it definately felt like it hit a fuel pump cutoff every time at 4100RPMS, or EXACTLY when the tach hit 6000RPMS. There is definately something there, and my dad said it feels like the fuel pump kicks off for a split second.

The A/F ratio was done at the dyno. The guy put in a tube attached to a machine that sounded like it had a pump in it. Not sure how it works, cause I don't know the first thing about dynos. It also had 2 bottle attached to the machine. It was a complete seperate unit from the car and did not rely on any of the car's data.

Those numbers are RWHP and RWTQ.

How can the dyno numbers not be real? Could the placement of the tires on the rollers make that much of a difference, or do you mean you were thinking I was making them up?

Could the clutch be the reason I can't break loose? But there is no indication of slippage.

No codes were thrown and all the injectors are firing normally.

********Another note: At idle, the A/F ratio was around 16:1, which I understand is a tad lean for idle, then it drops like a brick to 10.2:1 at WOT after it hits 3000RPMS, any reason why it's running rich at WOT and lean at idle?*********

 

Also, sorry for the double post, but would a partially clogged cat and stuck EGR cause the lean idle/rich WOT problem, because I believe the cat and EGR are both defective.

 

Anyone???

 

Well, I guess I'm asking for too much help.

Thanks anyways.

 

There's a definitely something wrong here.

Your tach is reading 1900 rpms high? You're getting a 10.2 air fuel ratio?

Hard to figure how he reading could be off by so much..

With a mixture THAT rich there should be other indications as well; maybe smoke out the tail pipe, fouled plugs and the engine probably wouldn't pull cleanly.

Tell us about the dyno shop that did the testing. The answer may well lie there, with their equipment, calibration and/or operator.

Before I'd assume there was something wrong with the engine, I find a way to verify those very out-of-spec numbers.

Jake

 

The place was Dyno-jet Inc. off of airport road. It's listed on DynoJet's website.

The cars pulls good, but just can't spin the tires. I can keep up with my friend and his 2001 Mustang with K&N and Mangaflows, and can get about a car length ahead of him by 50, and thats with me shifting at 5000RPMS according to my tach (or 3300RPMS in reality).

I dunno, the dyno numbers could be off, but I don't think the A/F ratio would be if it was a seperate system.

 

I know this is bad for the clutch but I have to ask.... have you tried revving it up a little and dumping the clutch to get any wheelspin? What happens?

 

Do you have a cool thermostate? Sounds like the enrichment circuit is working overtime on top of WOT signals to the ECM. Usually the A/F ratio on the dyno is pretty acurate.

 

I have the stock 195 degree T-stat.

I can burnout easily if I rev it up from a roll and dump the clutch. I hope its not as bad as just dumping the clutch from a stop (can peel then easily too), because I did that about 3 times.