dizwiz24

2 years later, Im still trouble-shooting as to why my hotcam'd 93 vert (ZF6, no cats, no EGR) LT headers and Ed Wright chip) runs so rich at idle.
I say no cats, but keep in mind it also did this with cats and EGR as well (although not as bad).

The exhaust smells so bad it makes the car unpleasant to drive at times.

Just for kicks, I put my stock computer chip back in and its still nastily rich. In fact, it seems a little worse with the stick chip. .

Also, when scanning my car with the stock computer chip, at idle the right and left side integrators are as low as they can go (I cant remember what the exact value is, but 64 or something seems right). O2 sensor readings stay high at 850 mV. As soon as the car is rev'd up past idle integrators read normal 128's, O2s fluctuate, etc.

I should mention at idle with the other chips I have, the integrators read 128 and appear to function normally at idle, yet the exhaust still reeks of fuel and other nasty odors.

Ive already went with working heated O2 sensors, looked for spark arcing of the wires, but cant find whats going on.

Another thing Ive tried is going with a chip that had actually more fuel at idle (maybe I was too lean at idle and interpreted it as too rich). This did not solve anything. Neither did chips with less fuel (lower VE) at idle.

Is this just a characteristic of any cam that is more aggressive than stock? Bad idle smells?

I knew poor idle quality was one drawback to a larger cam, but I didnt realize that smelly idle was another.

ANTI VENOM

My take on this is: There may be more smell than stock, but after the car is warm, I wouldn't think you would smell it while driving around. My car has a larger cam than yours, and the only time I notice the smell of gas is when it is cold and in open loop. Are you sure that the ECM is in closed loop when idling? The rich BLMs would be down to 108 and the lean ones would be up to 160. Give us a scan so we can take a look. Maybe one of us can catch something that you didn't..

dizwiz24

Scan tool confirms it goes into closed loop quickly and stays there.

I installed heated O2 sensors (i verified the heaters work too the other day) to further improve O2 sensor performance last year.

No such luck.

Everything indicates to me it is running rich.

Im almost wondering if I have a fuel injector problem?
Yet, resistance tests fine for all fuel injectors.

However, this never happened before I went with the hot cam...

JAKE

I agree, posting the scan numbers could be a big help. I know, I sound like a broken record, but it's all about the numbers.

The HotCam you're running shouldn't be causing what you're experiencing unless it was installed incorrectly.

A vacuum reading is in order too. Other guys running the Hot Cam cam check your reading against there's to see if you've got a vacuum leak.

Jake

65Z01

The fact that the Integrators are way low indicates the ECM is seeing a very rich condition and is trying to lean it out.

Have you serviced the IAC pintel & bore to assure it can get enough air at idle?

How about manifold vacuum at idle?? I believe your engine still has a MAP sensor but don't recall it it had a MAF again.

Are you running stock injectors??

Though a "lean" chip didn't get rid of the smell, what happened to the BLM and Int values. First get those numbers in the ball park and then attack the odor issue. Odor could be due to another issue, like a bad cat or two.

rrubel

This is probably obvious, but I've been doing some reading on tuning EFI and remembered this (very long) paragraph. The important bit is at the end.

"VE – Volumetric Efficiency is a term that corrects for different engine efficiencies. An engine is basically an air pump and the better the pump, the more power it can generate. Some engines are better pumps than others at a given RPM and MAP condition, so this term allows the equation to be calibrated for different engines. This is the single most important term that a speed density EFI system is famous for. There is a table in the ECM EPROM (chip) that gives VE for a given RPM and MAP condition. The important concept to grasp here is that the VE table is used in both open and closed loop modes, and essentially all modes. What is not so obvious to a novice is that this table, when programmed correctly, will result in a 14.7 A/F ratio with no closed loop or open loop correction taking place. In other words, this table provides a baseline that tells the ECM where 14.7 A/F ratio is so that other A/F ratios can be commanded and the ECM will be at the desired AFR. When this table is adjusted correctly, the engine runs the smoothest, not because the engine is running at 14.7 necessarily, but because all other ratios depend on this table being accurate. If this table is off, the closed loop term will correct the A/F ratio back to 14.7 to a degree. If this table is way off, the closed loop term can’t compensate and the engine may not run period. A good example of when this table needs adjusting is when a hot cam is installed. A stock cam typically idles at 17 inches vacuum. But a hot cam might idle at 15 inches or less of vacuum. The VE table will be calling for more fuel at a lower vacuum reading (higher MAP), but the engine doesn’t need the extra fuel because its still idling. In this case, the calibration doesn’t match the engine’s airflow characteristics. Unless the VE table is changed to lower the efficiency at this MAP and RPM, the engine will run very rich and probably stumble and blow black smoke. The majority of retuning a GM EFI system for non-GM and non-stock engines is done in the VE table since this is the baseline of the entire system. See Figure 1 for a sample of this table."

FWIW, it's from this page.

[RICHR]

steve1ph2

well rrubel, thats seems to have rounded all the chickens up into one nice neat clean pin. now picking the right one is the only problem. really thanks for your research. even though all that is in the service books its spread out over a few hundred pages. my `90 is doing the same as dizwiz24 all the same the smell the richness the stumbling... ever since all the mods. cam ( 224/230 at .050) stroked ect... the last thing i attempted was the heated o2. dizwiz24 unplug your 02 and the car will run like a champ but rich. iv done that at one point for testing purposes. so seems that other than chip work maybe we could trick the ecm by fooling the map with maybe a vacume pressure regulator or something

tjwong

I beleive that the reason that your car is running rich at idle is because the mail order chip from Ed isn't spot on for the idle regions. Your model year engine has a Speed Density based fuel strategy. This means that the fueling for the engine is based on engine speed and manifold pressure. When the hot cam was installed the basic VE (volumetric efficiency) of the engine was changed. Where with the stock cam it probably idled smooth and content at about 650 RPM and at a MAP value of around 35Kpa or thereabouts. Now with the new hot cam it is idling at a different idle speed, I suspect around 750 or 800 for one of Eds chips. And the idle MAP value is probably around 45 to 50Kpa. The higher the MAP value the more engine load that the ECM is thinking there is. At WOT (wide open throttle) the MAP value is 100 to 103Kpa. 100Kpa is basically equal to one BAR and one Bar is basically equal to one Atmosphere or 14.7 PSI atmosheric pressure at sea level.

You will probably need to reprogram your chip to get the idle fueling straightened out. In order to do this you can either do it yourself by getting the software and hardware to burn a new chip, or get someone locally with the equipment to do this for you. In order to do this via mail order it will take a couple tries by the vendor to do this. Most people like Alvin at PCM4Less can do this if you can provide a scan of the engine at idle. Going by what you said the fuel trims are, the ngine is pig rich at idle. I have three or four 93 LT1 cars with hot cam setups and I haven't had a problem like this with just my generic chip. A hot cam will have a slightly rougher idle than a stock cam but its really not rough at all as far as radical cams go its very mild.

MtlSphere

So what does Ed Wright have to say? Have you contacted those folks?

JAKE

Oh, I forgot you're running a MAP system. Yep, I've read over and over how those systems lack the ability to adjust to engine mods the way a MAF system can.

I'd scan and save the data to a floppy and send it to Ed Wright. Could be all you need is some PROM tweaking.

Jake

steve1ph2

so do you think there is any way to fool the map? there just has to be a way around a simple input? maybe it will work maybe it wont. im for the chip work no matter what. its really the only way to do the job right. but what if we could find a work around?

JAKE

I don't know of any, sorry.

Jake

93 ragtop

I sent you a pm on this subject.

ANTI VENOM

I have the 224/230 in my 350. There is no need to trick anything. Tuning, tuning, and more tuning. Good luck!!