hey guys,
got a problem with car cutting out badly from 1/2 to 3/4 throttle. part throttle and WOT works great. I have had this problem from stock tune and multiple other tunes with most of engine mods listed below in sig. it's seems to run very well, except when I'm between 1/2 to 3/4 or so...then it just doesn't know what to do and bogs and cuts out and all sorts of nasty not fun things. ANY ideas???
bad TPS???

thanks in advance!

 

Hi Interceptor, Could be several causes. But may be a TPS issue. Do you have access to a lab scope? If so, back probe the TPS signal to ground and watch the voltage from closed to full throttle. Should be about .5v at CT and ramp smoothly to about 4.5v at WOT. Look for drop outs or glitches around 1/2 to 3/4 throttle. Hope this helps.

 

yeah I actually have a lab scope at work (ASE mech.), but didn't know if this may be a tuning problem (which I'm not good with computer tuning, probably should of posted in DIY PROM section.), but that's what I was thinking, felt like a TPS problem, which is not uncommon.

 

Have you scoped the TPS? If not start there. Could be fuel or spark map but more likely a sensor issue. Is it speed density or MAF. MAF sensor or MAP sensor. Check these out using the lab scope. Snap on Vantage will give you sensor ranges. Dont worry that yours is modified. Sensors still read about the same. Good luck.

 

I replaced o2 (haven't in a while) and tps (had small glitch, but not the issue), still have same problem. I have MAP sensor, but haven't scoped it. I have a vetronix mastertech that works well I can scope with. Question though, it feels like the timing out during when it messes up, I wonder if the knock sensor is pickup up false signals??? I will check that too. I did find some more info on when it does it.....above around 2k rpm till about 3700rpm, and only part throttle over 1/4 to 3/4.....I wonder if the tune is set to run knock sensor then and is picking up valve drain noise or something?? Don't know yet, need to call tuner (pcmforless) and see when he programed the KS. I know he de-senitized it, and I could run a LT4 knock sensor to help further not pick up false signals. Anyway, I'll check those sensors and go from there, it might be in the tune, but hope not, well keep the ideas coming!! Thanks so much.

 

Knock sensor can affect acceleration by pulling out 18 degrees advance. Shouldnt cause engine to drop out completely though. But if youre concerned, watch data stream during the event and watch for knock retard. Fortunately for me, I was able to disable the ETC on my ACCEL gen 6. My knock sensor was going crazy from valve train noise. I was getting 18 degrees retard on any hard acceleration. Robbing tons of power. Car was still fast though even then and ran well. Just not as scary fast as it is without the retard. Are you in love with your control system? Youve built a great motor and car. Would you consider a wide band programmable ecu? Holley makes a good system. You could adapt it to your motor without too much trouble. How are you at electrical?

 

Sorry, I made an error on my last reply. I disabled ESC (electronic spark control/knock sensor system), not ETC (electronic timing control). Big difference.

 

I wouldn't be opposed to changing computer but was worried about the cost.....
also, how did you diable your esc system?? does the computer still adjust timing or did you lock it out completly?? curious about that. thanks so much for your help.

 

It could also be a tuning issue. The VE could be off, the timing not right. This is especially an issue if your running SD as those have to be tuned on the spot using datalogged info from the engine and a wideband, as opposed to thru a tune via mail company. Can you scan teh ECM, do you have a wideband?

 

I have a data logger but no wide band, but there is a local mustang guy who can datalog everything on his dyno, just not burn my chips since he does not have the equipment for mine.....I thought about going into tuning myself but a bit nervous that I won't know what I'm doing. The mail order chips have always done well, but this is the biggest build I have done, alvin had said he needs a more info, like the data logs and dyno runs to get the tune better....it has come a long way from the start, getting better, but I would love it to run perfect, lol.

When I ordered my aldu (I think that's what it's called), the cable from computer to laptop for datalogger, I did notice on their website they have a 'chip burner' for like $85 that burns the same style chips I have in my computer, I wonder if I should purchase, find a tuner program, and try myself???? alvin at pcmforless did get me off to a good start. website is moates.net link>>> http://www.moates.net/index.php?cPath=64 I am using the G1 memory adapter and SST chips.
when you say wideband, are you talking about a gauge or hooking to data log, or are you talking about replacing the narrow band for the computer with a wide band???
I'm on a slight budget, so I don't know if a wideband gauge is something I can do soon, I have a narrow band gauge in the car now. (just dumped a couple thousand on car and emptied car fund,). Sorry for twenty questions, newb at the tuning end here.

 

oh, I noticed that toward the bottom of that page of the link above......there is a NVSRam module kit that was developed by montecarslow from this website, I wonder if that is something tolook at too, kinda lost with all of it.
Check this link out.....it has some very interesting info in it and I'm interested in the real time tuning that it has...
http://www.moates.net/nvsram/Site/Main.html

 

On the ACCEL gen 6, The esc/knock sensor system is an option and can be disabled for more radical cams. The EST or timing control is seperate from the the knock sensor system. I still use the ECU's timing control but without the ESC. My cam is a hyd. roller 242/242 deg@ 050, 560/560 lift on TFS twisted wedge heads. Noisy valve train. But Ive been thinking about your issue. Your factory ECM has three seperate operating modes. Idle, part throttle, and wide open throttle. You may well have an issue with your part thottle, closed loop, fuel map that doesnt affect full throttle or idle. You say you have a data logger with wide band O2. Use this to monitor AFR at idle, PT , and WOT. See what you find out. You may have a bad O2 sensor thats causing a problem in closed loop. The ECM drops out of closed loop at idle and WOT. This would explain your problem.

 

Sorry, just reread your post. No wide band. But you can still see if O2 goes lean at part throttle. You may want to try testing your O2 sensor by disconnecting it. This puts the ECM in fault/calmap mode. See if the problem goes away. If so, replace your O2 sensor. In not one for throwing parts at a problem, in my profession thats bad business. But try the O2 test I described.

 

91interceptor, Im having the same exact problem no joke!! Identical to wat you explained up top. And something kinda crazy, i have the same cam as you and same heads.(sig below). I can just had my car tuned at TPIS in chaska, MN and they did not have an answer for me other then throw a new fuel pump in it ha. So i was like great there tryin to get me outta here cuz they dont wanna mess with it. So now im stuck too. BUMP, i need info too!!!

 

ASEdoc, good thoughts, i did just put a new o2 sensor in a couple days ago, was thinking the same thing you were. I found a guy with a dyno that he can cell load it and I can run the engine at any rpm and load, charges $175 per(wow),but I can data log some serious info on here, and he has a wideband I can use there to get a more acurate reading. I wnder if I should disabe esc ks. might have too.

cody, that's funny you have same setup with similar issue...I'll for sure keep ya posted on any progress I'm making...I WILL figure this out for sure, just might not happen overnight, I use PCMforLESS to tune my chips but might by a chip burner from moates.net or even a programmable computer (NVSRAM module) (about same price) but don't know if I am good enough yet to program my own stuff all by myself.lol. I'm sure it's something simple that can be changed...(I'm still thinking something is setting off knock sensor), just have to narrow down to what it is.

 

Hi Interceptor, Sounds like a good plan. Data logging with wide band on the dyno should get you to the answer quick. As far as disabling esc, disconnecting the sensor will put factory system in full 18 deg retard. But you can remove the sensor from the engine block and tape it back to the harness to eliminate esc ( a TSB repair on some GMs). One thought I had, ignition drop out can cause symptoms alot like yours and it can create confusing O2 data. An inline spark tester on the coil wire and then on a plug wire or two will find it. Just a thought. Good luck.

 

Hi Cody, Before you go too far, I wouldnt completely disregard the boys at the horsepower farm. A cheap fuel pressure gauge and a trip around the block while watching it could save you some greif. A 500hp engine needs a serious fuel supply. Dont overlook it. Hope this helps.

 

Ase doc, thank you for your comments! Greatly Appreciated!! Now, when i was getting the car tuned that was one of the first things we did cuz he was thinking the samething about my fuel pump (that i would need an upgraded one with wat i was running) and he said he had it set for 45 psi and on a full throttle pull it dropped to 42 psi or somewhere around there. But he said it would be fine for the time being but i no i need a bigger one asap!! thinking a walbaro 255lph if that would be a good choice.

And thanks 91, im gonna post wat i do to my car too, to help narrow down the problem!!

 

ASEdoc, I was contemplating the ignition system as well....I was thinking about what the car is doing...and thought of ignition. I have a MSD 6a with blaster coil, MSD cap and rotor, throught msd wires but on a stock dist. and stock ign. module. I was thinking maybe the pickup was maybe having an issue...it's not uncommon, but havne't seen it throw the symptoms mine has, but that doesn't rule it out. Also, another thing I haven't changed in a while, spark plugs. I wonder if I can scope it (or if the multispark from msd would throw off scope??), but only seems to occur under a load, so might not show up on scope....visual inspection of the pickup shows it to have a bit of smooth surface rust, but nthing obvious, but good idea to check that....I figure if I elminate all the common stock isssue, and it doesn't fix, then would point toward the tune. I'm still waiting for good weather and for a new set of header gaskets before I can datalog anything (it still did it before header leak, so not that)....thanks for the info, keep ideas a coming!! I'll keep ya updated.

 

ok, I data logged the info. We did 2 hrs worth of running. found NOTHING according to the info. Every single parameter is PERFECTLY in specification of where is should be. I mean not even a smidgen off, I also used a scope on a lot of the sensors and tested a lot of them. So the only thing I can think of is the distributor, we had a similar problem at work with a chevy truck, and everything tested good, ended up changing distributor as last resort and it fixed it, so I'm going to try that, it's old anyway.

 

Hey Interceptor, Yeah that sounds like a good plan. I was looking at some old repair archives and ive seen alot of hei failures. Especially with aftermarket coils. I see you run a 6a. That takes the current load off your stock ign mod and basically uses it as a cam sensor. Still any stock ign part is a weak link. Sorry the dyno w/ datalog didnt show anything. What a drag. Hope the dist fixes it.

 

alrighty, took out distributor, for sure a lot of rusty metal shavings underneath pickup...and the shaft turns very freely, no resistance from the magnetic pickups, the thing looks old and worn, so "I'm suspecting that is my problem, waiting on new dist. to arrive and then hopefully that takes care of the problems....crossing my fingers anyway.

 

So how did things turn out? On my motor it bogs/missfires from 30%-50% (Info from scanner) throttle. Idle and slight throttle is fine. WOT is fine but its that in between thats killing me. My motor has about 5000 miles on it and this is a recent thing. I was suspecting the TPS or distributor.