Great power at all throttle and rpm but at wide open.It runs great but at wot it stalls bad.No codes, great cold start and idle.All the stats are good but the o2 is reading at wot is in the 800mv + range.

 

The stock O2 reading is not a good indicator for WOT.

What are the engine, fuel system specs? Falling flat at WOT is most likely lean.

 

The motor is a 400 sbc,30lb injectors,ported plunum,l98 cam,tb bypass,air intake sensor relocated,flowmaster exhuast.The vitals are perfect all the time,mas not maxing no codes fuel 42psi.I did'nt put on an afpr on it yet because I thought the 30 lb squirters would be enough.How can I tell its running lean?The prom seems like a perfect match.So I tend to think its not the programing in the prom.

 

Lets say the stock 305 chip and injectors proved enough fuel for 230hp (92 305). Moving from 19lbs/hr injectors to 30lbs/hr units is a 57% increase in fuel, all other things equal. Thats enough fuel for 360hp with the stock prom.

The first test I'd do is raise FP and see if WOT performance increases. If you run faster, you are lean. Check FP at WOT to make sure FP isn't dropping.

Really you should start rich and tune towards leaner. Start with FP way up(assuming the pump can keep up) and reduce as performance increases.

 

Brent's correct; that your displacement has increased just under 33% while your fuel has delivery has increased 57% (possibly more if those are SVO injectors which would act more like 33#, using the method GM rates their injectors vs Ford).

Also, you give absolutely NO DETAILS about your engine. Cam, heads, intake? So it is difficult to determine what your flow requirements are.

Brent is also correct that you should not rely on the stock O2 sensor for fuel requirements. But, IF it were accurate, it would suggest you are lean, as Brent mentions.

I don't necessarily agree with compensating with FP alone. FP does not increase fuel delivery linear.

 

Agreed, raising fuel pressure certainly isn't the best way to handle WOT fueling. I would think it is a decent way to get a *quick* bearing on where you are at fueling wise as long as the fuel pump can maintain the pressure.

 

Stock 400 74cc heads,l98 cam,ported plunum,flat top pistons.I don't understand the dicplacement and fuel delivery point.If the cid is 33% increased and fuel delivery 58% would'nt you be saying I'm running rich?The fuel delivery 57%would exceed the dicplacement 33#.I will check for pressure drops though.Do you think my ac delco fuel pump will live at 50psi?

 

The motor runs perfect at all speeds and rpms.But running lean would make it fall on its face?

 

Formula, that is EXACTLY what we are saying (your fuel exceeds your displacement)...but there is more to it than just that, that is why you also have to look at what the mods are...which in your case appear fairly mild for a 400.

However, IF your O2 sensor COULD be relied upon, 800 mV is actually a little low.

Only a WB O2 sensor is accurate though. The 800 mV is kind of meaningless and it could actually be much different.

[This message has been edited by Glenn91L98GTA (edited August 30, 2001).]

 

Maybe I should have worded that better.The car runs perfect and I think reprogramming the prom isnt the answer.Thats why turning up the fp sounds right.The motor will run its **** off 1/2 3/4 9/10 throttle.Just that 1/10th couldnt be the prom,yes no.Considering the fp is fixed at wot,that does seem to be the problem.The fuel pressure was lower the first year of tpi.What about my ac pump at 50 psi?

 

Then this has nothing to do with Eprom Burning. I suggest that you ask the question on the Tech General or the TPI Boards then.

So before I lock this thread as this is DIY PROM Burning (Vader gets angry when we answer his Tech questions), just remember that when you are in Closed Loop, the ECM will make corrections based on the O2 sensor (which is why part throttle feels fine). At WOT, the ECM ceases to correct based on O2 sensor. This is when you see ALL the problems with the eprom as now you rely on the accuracy of the calibration within the eprom. Which is why you are experiening the problems that you are.

You are trying to come up with a "mechanical correction" for WOT which says your Eprom is not right.

Why do you think GM has a different eprom for a 350 and a 305?

[This message has been edited by Glenn91L98GTA (edited August 30, 2001).]

 

ultimatly the prom will need need burned but I did'nt think the tpi board could answer if the pressure raised would help for now(or that would indicated a need for prom ajustment).

 

I really hope help on this board does'nt end up in "there is a reason for 305 & 350 eproms,duh".It just semmed a little harsh

 

Besides there is no production 6.6l eproms.So if I want to find what needs changed in the eprom,I can use my mechanical trick to help.

 

SD (which you have) calculates the amount of time to keep the Injector Pulse Width based on a number of parameters in the eprom. One is Displacement and the other is the size of the Injector.

The 350 has a different displacement and injector size than a 305 and (guess what) so does their eproms.

Has the light clicked on yet?

 

has the light clicked on for you ???in 85 there was no sd tpi.Mine has a mass airflow sensor,heard of one?

 

That is why guys with "stroker motors" need to get a new eprom.

Do as you wish, but you will not perform as you ought to. All these "mechanical methods" arose in the 1980s because no one knew how to burn an eprom (except a few techies that made big bucks...and then they generally didn't do a very good job as they didn't know what we know today).

This is the primary reason so many guys that should perform a LOT better based on their mods are so slow. And then they want to know "what's wrong with my motor" when a Mustang beats them. Maybe that is why Mustangs were so much quicker than F-bodies back then?

But I am here to talk about eprom burning, as I said Vader gets mad at me when I start stepping on his turf and I get a nasty e-mail from the Admins saying "you should have locked that thread". Right now, you are not talking eprom burning and technically I SHOULD be locking this thread.

 

My mistake, I thought you were the guy with the 92 (I've been answering a TON of questions).

Well, guess what, you have even a bigger problem. MAF maxes at 255 and you don't even have eprom calibration then, now you are running on luck.

Good luck and see you on the Tech General Board.

 

Vader (Jeff) this one is for you.

 

Now that this post is on the proper board, I will answer this and you don't even have to worry about me using my Moderator Powers.

Some background. MAF does not need to know the displacement because it measures the incoming airflow. Thus, whether it is a 305, 350 or 406, their fuel requirements are "basically" the same at the same gm/sec reading. The only thing that happens is that rpm level where a 305, 350 or 406 experience a specific gm/sec airflow is lower the higher the displacement motor.

As long as you use the SAME injector as defined in the eprom, all is fine, provided you haven't maxed the MAF. You may need to do some tweaking to the MAF Scalar tables and some compensation if you have a lumpy cam for "reversion" (plus "pump shot"), but these are just "driveability" issues. Some are noticeable, some are not. Depends how picky you are about the "quality" of the idle and ride.

However, if you have changed the injector size without telling the eprom, MAF will give more fuel than it should. Thus you will run rich. It is not a displacement issue (because MAF doesn't care about engine displacement...just the airflow and matching injector size). At part throttle, you the O2 sensor is correcting for you (regardless of whether you are maxing the MAF or not), it sees that you are giving too much fuel, so it will lean/shorten the injector pulse width. The only clue will be if you hook a scan tool, you will see very low BLM values indicating the ECM is leaning for you. Your real risk is triggering an SES code for an overly rich O2 sensor reading).

All of the above is when you are in Closed Loop and the ECM is correcting for you. As I said, provided the BLMs don't go too low and trigger a "Rich O2 Sensor reading", all is well (kind of..there are some issues there too...but for this simplified discussion, I will leave it at this)...WOT is the real problem.

At WOT you have two issues: Have you reached 255 gm/sec or not.

As long as you have not hit the 255 gm/sec limitation, you engine will run rich...no doubts about it. This is because the O2 sensor is not correcting and the ECM is thinking you have a smaller injector that it should. Under 255 gm/sec, your 406 will run the same as a 350 and a 305 would with 30# (or 33# if SVO) injectors...RICH. Under 255 gm/sec, MAF does not differentiate between a 305, 350 or 406...they are all the same as far as MAF is concerned.

Now, here is the tricky part, maxing the MAF @ 255 gm/sec. Once this occurs, you have no further correction by the O2 Sensor (since you are in WOT) AND no further compensation as the ECM cannot detect any additional airflow. So you begin to get leaner and leaner based on how much air is REALLY flowing through your engine. If you flow too much air that overcomes the richness of those 30 (or 33# injectors) when the ECM is thinking they are 19# injectors...

 

the maf is not close to the 255 limit now .with more mods it will come into play but this is my starting point.I guess I'll make my afpr thanks to that great tech article.I guess that might help for now.What about icing down the mat.would that help me get that little xtra(its been relocated).

 

I will let Jeff answer the last part.

 

the maf is not close to the 255 limit now .with more mods it will come into play but this is my starting point.I guess I'll make my afpr thanks to that great tech article.I guess that might help for now.What about icing down the mat.would that help me get that little xtra(its been relocated).

 

Based on your posting time, I don't think you have read my response. I think you should.

 

PS: A relocated does nothing on a MAF car, only SD cars.

 

Well, the MAT doesn't do EXACTLY nothing on a MAF car. It controls the enabling of the EGR based on the temperature reading of the MAT. But it does not add any additional fuel. The MAF sensor actually makes changes changes to air flow both on temperature of the incoming air and (believe it or not) humidiy. Unfortunately, it doesn't do it accurately.

In high humidiy, the amount error for detecting airflow can be as high as 10%.

This is why guys with "large" SBCs often convert to SD. This weekend, I will be developing a "temporary" eprom for a buddy with a 383 stroker (AFR heads, large cam, Miniram) that is currently running MAF. The only way we can compensate is through PE (WOT to the ECM). But it is "blind" beyond 255 gm/sec, and we know this. This is strictly temporary, until we convert him to SD. SD can work on any displacement motor up to around 8.0 Liters.

The problem with both MAF and SD, is when you get into large volume injectors. High impedence injectors can only go so far and then they introduce their own problems...plus they get expensive.

Now that this post has hit "hot" status, you will get the readers.

[This message has been edited by Glenn91L98GTA (edited August 31, 2001).]

 

Glen's dead-on right. MAF cars HAVE TO KNOW THE SIZE INJECTORS THEY ARE RUNNING!!! If the chip thinks it's got 19lb injectors (it does) it will open up the pulsewidth to what it thinks it needs to match the airflow (it measures with the MAF. Meanwhile, what seems like a "huge" change moving to 400 cubic inches is relatively unimportant to a MAF FI system. All it knows is AIRFLOW and how to correctly match FUEL FLOW to it. It cares not a damn about what size motor is under it.

Long story short- large changes in injector size drive MAF FI systems NUTS! In closed loop it'll compensite via the O2, but wide open you'll be way rich.

Formula5- here's my suggestion. You aren't going to like either one and probaly a few people will call me nuts but nonetheless, it's the right thing to do:

1. Custom chip to work with the bigger injectors. Your best bet. I ran a TPIS custom calibrated chip in my brother's 1987 MiniRam injected 409 (same basic FI system as yours) with SVO 30# injectors. The fuel curve is dyno verified 12.5:1 A/F ratio from 2000 to 6100 RPM at WOT without even a tenth variaton.

2. Put the stock 305 19# injectors back in. I can hear people screaming from here!! But here's why it will work: You're not close to maxing out the MAF so you probably won't max out the 19# injectors either (100% duty cycle). You'll be damned close to maxed out with even a mild 400 but it will run WAY better than with those 30# units in there. The calibration of the chip will once again match the actual flow rate of the injectors and, as I mentioned before, that's what matters most to a MAF-type FI system.

 

The stock injectors are original.One is cracked & the others ar not much better.New ones would cost more than the prom burning hardware.your right about the stock 19lb would work better w/ the 305 prom.I'm just going to go the cheap route an get the hardware.My 400 will ultimatly run better w/ 30lb injectors and self burned prom.my 30lb accels will be a nice platform for mods too.It'll also be nice to get rid of that stock l98 cam.Then I'll have to watch the 255 mas limit.I just want it to rip at wot for now.It grabs a hard second but could be peeling in second.

 

Maybe I should have worded that better.It could rip that puny 10 bolt to shreds.

 

The internet is a better place having glen and thirdgen.org.I cant wait to burn my own prom.Glen,thanks for all the info!I will be back.

 

I'm going to add my $.02 here, since I'm experiencing the EXACT same situation. I put a 350 into my 85 and I'm having identical issues. The car is decent at part throttle but a pig at WOT. My plugs are black and so are my tail pipes. I've got 24lb/hr SVO injectors and the stock 85 computer and PROM. I talked to another 85'er with the same problems. He went back to the 19lb injectors and found huge improvements. The 85 ECM/PROM is calibrated for specific fuel deliveries based on the 19lb injectors. My 26lb (24lb SVO = 26lb GM) injectors are way, way, way too much for the 350 with the original calibration. Lowering the fuel pressure could help compensate, but going below the stock 42lbs isn't an ideal situation. I thought about having a PROM burned, but the more I learned about hte 85s, the more I realized that the 85 ECM is just way too primative. I'm now in the process of swapping over to an 86 ECM and installing a PROM from an 87 L98. I expect substantial improvements in drivability and power. Once I get that done, I'm going to start burning my own PROMs.

It seems that you're hell-bent on solving your problems with a fuel pressure adjustment dispite having everybody reccomend otherwise. I would strongly suggest that you upgrade to a newer ECM, but at the very least you need a new PROM. Changing your fuel pressure may be a good band aid, but it sure isn't a cure.

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You really need to hook Diacom or something up to it to see what it's doing.
I put in a 383 and have started burning chips for it. If you want help with yours e-mail me.
Where in STL are you? I am by 70/170 interchange.

 

I'm really hell bent on finding the reason for my bog,thats all.I really don't think it's the injectors bieng too big.If that was the case then could I get 25 mpg.I just went on vacaction and thats what I got,25 mpg.If it is the calibration though,I'd rather adjust the prom then lower the fp.

 

My spark plugs ar burning clean also.

 

I do have my base timing at 8d btdc.Would that be too much total timing at wot?