I've done some searching, but can't seem to find what I'm looking for. The problem I'm having is that at 100% full throttle, my vehicle sort of planes out and won't accelerate. If I back off the throttle just a hair, it will accelerate again. This happens all of the time, at any MPH, whenever the pedal is pressed down all the way.

The engine is a new (800mi) GMPP crate 350 with a roller cam, Holley TBI, headers, vortec heads, and a K&N intake system. I'm very new to the world of tuning. I've burned 3 chips so far and all are variations of the hypertec chip that came with it. I'm using the Autoprom with a 27SF512 chip.

What could cause the problem? I'm using a new walbro 255 fuel pump, so I don't think fuel is the issue, unless it has something to do with the VE table. My gauge hardly moves when I goose the throttle.

Would timing be affected at such a small TPS% decrease while still in PE mode?

Any help is much appreciated. I'm going back to reading more of this board. Thanks.

 

The VE table could be off in the upper MAP areas causing a rich/lean cond., the timing table could be off in the upper MAP areas, it could be leaning out at very high loads, the injectors could be static, it could have to do with the PE AFRs causing the engine to go rich once PE is engaged, etc... LOTS of things to choose from.

Can you datalog yet? Do you have a wideband? Might also be a good idea to check the TPS itself and make sure its OK and not acting screwy at WOT.

 

I've quoted part of your problem.

All the overpriced hypertech garbage does is add excessive timing where you dont need it, at WOT.

Also what size is the Holley TBI?

Further more, you may not have enough fuel flow at WOT due to the size of the injectors or due to your tuning.

If its laying down on u that bad, 90-1 its prolly knocking, do yourself a favor and go slow. Worry about the bottom end, idle and cruising areas befroe you attempt WOT stuff. It will save your new engine too.

later
Jeremy

 

Is there some way a transmission could do this??? Like if the TV cable is out of whack, or off.

I've seen that problem on a carb that had a broken cam for the secondary needles, and that was definitely a lean condition. Laying down from too rich is pretty difficult, but can happen.

Your bigger better engine is probably breathing more than whatever the stock hypertech chip was trying to fuel, so you're probably leaning out.

What ecu are you running? What mask ID?

 

Id guess that its either a 7747, 8063, or an 8746. The standard C3 TBI masks are all very similar to eachother.

If its a later PCM then its a whole new ball game. The PE fueling is entirely variable.

 

Wow, thanks for all of the replies.

I do not have a wideband, but I am datalogging. After posting this, I started looking at my datalogs a little more closely. I noticed that it seems to happen when my MAP goes past 100, probably because the table does not. Sound reasonable? If this could be the problem, how do I get around it?

This is actually a truck that this is happening to, but that shouldn't matter. It is a 7747 ECM and I'm using a $42 mask. I'm actually using two, because one of them doesn't have the BPW constant, and the mask that does is missing some other tables.

The Holley is the 670cfm with the new-style injectors.

I've checked the TPS, and it functions perfectly. The datalogs do show that when this happens (full throttle) the TPS is only at 87%. I'm right at .54V at idle, so adjustment isn't going to be possible.

Looking at the knock counts, there are just a few spread accross the board. I haven't started adjusting the SA table because I've always though I should work on the fuel first as long as it isn't detonating.

 

Just to be sure, only the $42 mask can be used in a '7747 ECM. Any other Mask in that ECM will not run correctly.

Not sure if that is what you are doing, or if you are actually using 2 different ECMs.

RBob.

 

The fueling is tied to the timing as it alters the VE's. Once the fueling is roughed in, then you can move onto the timing. Once the timing changes, then so does the fueling, so dont get too hung up on trying to make it perfect because the fueling will only change down the road.

 

Oh, OK. Maybe I'll work on the timing some now then. Of course, being new to this stuff, I'm imagining 128's accross the table before moving on, but only in a perfect world, right?

I'm using two different $42 masks, just the one ECM.

Any ideas on what to do about the MAP being off of the table?

 

If your fuel in the logs is close... say... + or - 6 from 128 then I would definitely check your timing. I'm not slighting the importance of fuel but I had problems trying to chase my fuel around because my timing was off. The mark on my dampener wasn't actually at TDC. Once I got the timing fixed it was much easier to tune the fuel.

I would start by using a positive stop method of determining TDC and mark your dampener. Then make sure timing is set exactly the way you want (mechanically).

As far as WOT power loss, I would like to echo what has already been said. It would also be a good idea to determine the specific threshold point at which you enter PE mode. It is probably a lower MAP than you think.

This is just my opinion so take it for what its worth... As long as the fuel is in a "good" range (very close but not perfect), then there is more power to be gained or lost in ignition timing. The hard part is that it is much harder to tune on the timing than fuel. A dyno is the best and unfortunately most expensive.

 

Ya, the dyno thing has crossed my mind a time or two. It'd be nice to take it somewhere and have it back the next day or so with one perfectly tuned chip, but even the dyno chips aren't perfect.

My timing marks were right on when I degreed the cam, so I know that's OK.

Like I said, I'm new to this, so how can I determine when PE mode kicks in?

Any pointers or tricks to tuning the timing. There's a lot of content on this site, so forgive me since I haven't read it all...yet.

 

The ECM only allows the speed density MAP to be 100 kPa and no greater (255 in the computer itself). This means that the ECM simply uses the 100 kPa entries, even if the reported MAP is somehow greater. It wont go off the end of the tables or anything like that.

 

So even though the problem seems to happen only past 100 kpa, that must be a side effect of some other problem? I'm thinking of adding a small resistor to keep the voltage down just enough so that the MAP doesn't go above 100kpa for testing purposes. At least then I could rule it out for sure.

 

i had a simialr occurrance this past spring early summer. i was running lean on WOT as determined by my WB logs. did a cam swap prior year and my WB then was damaged . lean means 13.3-13.5/1. that was after the AE timed out as it was 12.0/1 or richer before PE. W/O the wideband and if leaner yet in PE <13.5/1 i may have had similar results as you. not good! Holley i believe is 65 lbs rated at 20 lbs FP. maybe good for 250 -275HP? i suspect you need to bump up the FP to account for your HP estitmate. and then validate the WOT A/F with a WB.

i remeber running two strokes full throttle and engines slowed down @ WOT just b4 they seized.

check this out:
http://www.users.bigpond.net.au/ben_...ctorsizing.xls

 

The injectors are rated at 65lbs/hr @ 11psi. I'm running 17, so it should be good to 330hp or so.

I'm not sure how to tell if running lean is the problem without a wideband. I'm told not to bother looking a the O2 results at WOT with a narrow band because the results mean nothing. I did step it up to a heated sensor, so there should be at least some increased accuracy; it does switch a lot faster.

Also, when I back off the throttle a little bit (and begin picking up some speed again) the O2 results don't change a whole lot. I would think that even with inaccurate results, going from rich to lean would show something on the O2.

It only takes a 4% TPS drop from WOT to pick up speed again. I'm not sure if that says anything or not, but it is an observation.

 

i am of the belief HOLLEY rates their injectors at 20 lbs. Unless you have GM injectors then they are rated 12-13 lbs. anyway that is what i was told by Holley three-four years ago. i called them and spoke direct to a tech and asked if i can swap out the 65's for larger Holley 80's and we discussed their rating program.

on a side note. when i had a smaller cam i did not have a WB. i had 80 lbs inj at 13 lbs. underlying VE reasonably good. A/F commanded to 12.00/1 for PE. added WB and logged 11.9/1 and 12.1/1. so adequate fueling should give you the PE as commanded as i am of belief it is calculated off VE.

 

I posted the link of the ratings of the delphi injectors that holley uses over on the TBI board. Id have to dig a bit to find it.

 

I didn't know for sure, so before I started adjusting anything I had to find my BPC. To do that, I had to call Holley. Their tech said my TBI is rated at 65lbs/hr @ 11psi OR 85lbs/hr @ 21psi. I've been told that their old injectors couldn't be ran past 15psi, so it's a good thing I got the newer style. With the Walbro 255 pump and the regulator completely backed off, I can't get the pressure to drop below 15.

I think the new style injectors are delphi. I was told that they are interchangable with the Holley injectors.

 

I'd like to see what you find out to fix your problem. FWIW, I had the SAME EXACT problem a year ago. I never got it figured out. I went to the EBL and I somehow or another fixed it. I just don't know what I did. I have a similar engine, with a BBC TB and n2o. I do know that I still had a problem with top end accelaration, telltale in my trap speeds in the 1/4 mile. A 13.6 but with a 98 mph trap speed. Shuold have been more like 103 mph or something. I actually started to pull fuel out, the widband was giving 12.0 to 12.3 afr, It seems to like 12.8 or so without the juice. And it feels better. I just haven't had the time to get to the track again. O, and the total timing is like 33 d, anymore and it gets some knock. But then this is all with 87 octane fuel.

 

I'd watch your fuel pressure at full throttle. You say you can't get below 15psi, but that's probably at idle or key on engine off, and thus low or no fuel going through the injectors. When it starts to go through the injectors though, you might be able to get less than 15psi with the regulator backed all the way off due to the lower amount of fuel going through the regulator.

 

I only backed off the regulator to see how low it would go. It isn't all the way backed off now, and I'm running at 17psi at idle. Obviously I can't watch the pressure while I'm driving, but if I goose the throttle while it's in park, the gauge hardly moves.

 

Still haven't fixed this problem yet, but I have more information. A week or so ago I got the EBL system, and this revealed a lot more information about the problem that I couldn't see with winaldl.

Looking at the log, full throttle or just below, the map is the same, so I can rule that out now. I bought a new sensor before the EBL anyway.

My TPS% doesn't go above 90%, but like I said, just below "my" 100% it picks up speed. Looking at the log again, at full throttle, my O2 voltage is only 70-80mv. As I move my foot slightly off the pedal, the O2 voltage jumps to 870 or so on the very next row. So it stops gaining speed because it's lean, but what is making it lean? In both situations I'm still in PE, and the SA doesn't change at all. My PW is around 70 in these frames, so the injectors aren't static. I'm running about 22psi of fuel pressure so there should be tons left. I also noticed, that the INT and BLM seems to be locked in PE, though in both WOT runs I did they were different (125 in one and 130 in the other).

This happened before the EBL, so the chances of new and old bins being bad is pretty slim.

If the O2 is causing me problems (though it seems to be working and it is only about 1000 miles old) what would happen if I unplug it? (besides the SES light)

Once again, any suggestions?

 

To check if the injectors are static look at the DC% when at WOT. You mentioned the PW at 70, if this is 7.0 msec, they could be static. At 6,000 RPM 4.8 msec of PW is about 90% DC.

At WOT the INT is locked to 128 (no fueling changes). The BLM is locked at whatever it is. When it is below 128 it is not used in WOT fueling. When above 128 it is used to add fuel. The values of 125 and 130 are decent for a BLM value.

There could be a fall off of fuel pressure. Even the slightest drop off causes lean issues.

RBob.

 

I'm sorry, I meant DC%. The DC% at WOT during these two runs was about 70.

If the fuel pressure went down to cause this condition, why would it pick back up backing off the throttle? It's not lean any other time but at 100%tps. Looking at the logs, it's lean and then it's not, there is no in between. If the pump was the problem, wouldn't it be lean all the time it was in PE?

Could it be cutting the fuel? I mean, maybe it's going lean because the injectors are "told" to spray less? What triggers the injectors?

 

A possibility that the lifting causes the engine to pick back up, is that there is less airflow, so less fuel is required. This is the available fuel with the proper amount of incoming air. Then AFR comes back into line and the engine is running again.

The VE table may also be low in the 90--100 KPa area. If more can be added to the VE table(s) they should be increased.

Check the Rev-limiter RPM and MPH. This will cause the injectors to just stop supplying fuel.

RBob.

 

Ya, but a 4% decrease in tps signal shouldn't be enough to make the AFR go from one extreme to the next, right?

The log says that the MAP is still at 100% in both situations. At lower RPMs and higher RPMs, the problem still exists, so I guess it shouldn't be cutting fuel.

Does the distributor cause the injectors to fire?

 

RBOB: since we cannot log the high map and or high map high rpm tables how does one know what values to place in those cells? i did once turn off PE in my bin and run higher rpms with log. yes i was lean there 140-150 blm.

when i set up my VE tables in EBL i think i maxed them out. I believe i have 95 in all those cells of higher map and higher map rpm. actually i took the $42 VE tables from 7747 and moved it to EBL and added 10% in those areas as I was at 13.3/1 WOT pre EBL with 20 lbs FP at 80 lbs. so not only was i logging with new EBL but also logging the WOT lack of fuel reapproached with new EBL.

does the ECU assume those values are stoich and then factor in the PE multipler? if so would that not put my DC% at 100% and max out my injectors? if that is the case would i not then drop my VE tables in those areas so i see less than 100% DC at say 12.5/1 A/F at WOT. tuning WOT is difficult for me in that 100+ MPH comes too quickly!

 

Last question first: yes, the injectors are fired from the distributor reference pulses (DRP). This is in sync mode. Async mode just fires them 80 time a second no matter the RPM.

Try this: do a playback of the log of this happening and open the Malf Window. Check that the TPS isn't having any of the 3 indicator lights light. This is for both TPS Low & TPS Hi. This is just to make sure that the TPS% sensor itself is OK.

If you would like to email me a log file of this happening please do so. I'll take a look at it and see what I can see.

RBob.

 

Tuning the high RPM & MAP areas is best done with a WB. This can be accomplished in either open or closed loop. If closed loop is used then the BLM value will need to be taken into account. If above 128 it will be adding fuel. With that even if the BLM is 129 to 132 it isn't going to add that much fuel.

Can also log in closed loop with the BLMs locked at 128. Basically just need to get some WOT and near WOT logs.

Open the WUD and go to the Analysis screen. Scroll through or use the 'find mark' button to go to that area of WOT. You can now see the RPM, MAP, and WB AFR. Adjust the VE up or down as required. What you are looking to do is to get the WB reported AFR to match the PE mode desired (or commanded) AFR.

Keep an eye on the DC% as you go through that area. Can also use the graph function to observe the AFR. If you run out of VE head room and the DC% is still OK, then increase the BPC.

If you run out of DC%, then more fuel is required from the injectors. Will need to increase the fuel pressure or go to a larger injector.

RBob.

 

thank you. it appears i will need to patch the WB02 sensor into the EBL logs. i will at first run both NB02 as well as the output WB02 to EBL before i discontinue the NB altogether. make the EBL even a better tool. will reread my notes in spring on that as well as Innovate manual.

you state lock BLM's? and i assume watch the Integrator move. is it practical to log those high rpm/map areas? seems would be ***** out riding in 2nd or third gear of 5. might not be practical on the xway?

so if i read this right using a NB02 only and using fat high map -high rpm VE values in those cells, it will be assumed to be 128(stoich) by the ECU and PE factored off that assumption and BPC? so if the VE tables are really really fat(say 95 vs what they should be) in that high rpm/map cell, PE will be skewed richer than commanded in tune? if so i never witnessed it. last WOT run was as commanded 12.5-12.7 commanded to 12.7.

as a side note the WB02 shows richer with EBL than before EBL(13.3) for WOT only. same commanded 12.7. not sure why.

 

Well, I came home from work, popped the hood, and began to check fluids, etc. I also re-routed a few plug wires. Then, I went out to get a good datalog of the problem. Wouldn't do it. I installed this engine three months ago and it's done it ever since, but now it has stopped. I can't explain it, other than something was picking up interference from the plug wires, all of which are new and in great condition.

If it comes back, I'll be sure to get another log of it.