Racehead

This requires a little history so hang in there

The day I got my ASA cam in I loaded Marks tune in it just to get me down the road so I could check it out a little bit I didn't run it real hard since I wanted to heat cycle my new springs. Anyway it drove fine on my way out of town ( 1/2 mile or so ) , with some pretty good cam surging below 2000 rpm's. Once I got it out of town I stepped on it hard a few times, but didn't rev it over about 4000 rpm or so and it ran fine. As I was headed back home and coming back thru town it started bucking ..... now I know all about cam surge and had felt it on the way out of town, but this was MAJOR friggen' bucking even at rpm's well beyond where you normally find cam surge, even up to 3500 or so. About 30 seconds after it started I was home so I parked it for the night. Anyway I wasn't sure if it was just tune related or not so just decided to start tuning it the next day in SD mode like I had planned and see what happened.

Next day I unplugged my MAF and started logging some runs and making new tunes. I probably burned 1/2 tank out that day and it never bucked like that even one time other than the normal 1300-1800 rpm cam surge, which I tuned almost completely out. At the end of that day my laptop display went bad ( 1 month ago tomorrow ) so I haven't been able to do any tuning since then. At this point I kind of thought that maybe my MAF scaling being so far off was what caused the severe bucking I had felt, and since I still don't have my laptop back to do any more tuning I've been running the car in SD mode this whole last month, and have put about 300 miles on it. It has ran very, very well this whole time. Fast forward to this last Saturday.

After work on Saturday I drove the T/A down to Silvana to see if anybody was still around, nobody was so I called Boyce and drove down to his house to show him my new cam sound On my way home from Boyce's I ran into a Lightening and a WRX that both wanted to play. For about 10-15 miles or so I was sucking their paint off in the 1/2 mile gaps between groups of cars After about 15 miles of this and doing maybe 90-100 with just maintenance throttle I noticed this slight bucking going on. Within about 10-15 seconds it was so severe that I was forced to push the clutch in. When I let it out again the engine was smooth .... for about 3-4 seconds and then would start to buck again. I wound up driving the last 30 miles or so by pushing my clutch in and taking my foot off of the throttle every 3-4 seconds. This gave just enough smooth running time to maintain freeway speeds. If I tried just to drive thru the bucking it would buck so hard that I was afraid of doing damage to the drivetrain. I could actually hear the nashing of my tranny gears loading and unloading It would kind of clear up above 3500-4000 rpm IF I was at 3/4 throttle or more, but still didn't feel or sound right.I finally got it home and parked it. BTW this whole time it didn't throw an SES ?

Today I finally got a chance to look it over, check all my electrical sensor plugs etc. No problems found. I started it and it sounded very rough. I decided to take it out on the road and it started bucking again as I left my driveway. Within a few hundred yards it seemed a bunch better and now was driveable. Got outside of town and stepped down hard on the throttle one time and it gave one big buck and I immediately backed off the throttle. I did it again and this time it didn't buck. I immediately started to hammer on it trying to replicate my run in on the freeway and it runs perfectly now ?! Anybody ever felt anything like this ? Tomorrow I'm going to check my fuel pressure, my TPS with a Fluke , change my fuel filter etc. but I'm pretty limited without my laptop. I just thought I'd run this one past you guys to see if it sounds familiar ?

ram-it

Sorry to hear about the problems. I do think it is the tune. Relearn your throttle instead of doing the drill mod too. I had the same issues but not as severe. The drill mod took care of my idle surges and tuning took care of the rest. Mark's tune is not good for you since he has more air flowing plus is an auto. I tried a tune for the same mods I had but for an auto. I did everything to change it to a manual and it still did not work right. Changed back to my stock tune and started playing with the VE and PE tables till I got it like I wanted.

93TAWicked1

iTrader: (28)

Did you have your intake off during the install? Maybe your MAP sensor has a short in it? Mine had one of the wires pulled out and it would rev up big time then go down then rev up again... I never got it out of the driveway so I don't know how it would act if I would have driven it down the street.

Althout I do think Eric's idea of trying the stock tune is a good one...

Nate_Taufer

iTrader: (1)

ditto tune on your stock tune...much more effective than on someone else's tune expecting it to work...so much difference in the VE tables than you can expect to encounter. I suggest going back to stock tune than doing a SD tune. You should get close enough to daily drive without too many problems.

Nate

WAHUSKER

iTrader: (4)

That's a weird one Bill. Can't say my car has ever done that. You should have let me know, I would have brought up my laptop so you could log some data. I can do that tonight if you'd like.

Did you try plugging your MAF back in? Thinking maybe that the conditions you tuned for were very different than the other day, and without the MAF to compensate, your car's tune was out to lunch.

Or maybe it's bad gas. Throw some Beano in the tank.

Racehead

Guys I'm NOT running Marks tune. I just threw that in to drive it right after the cam install and that's all. The tune in my car now is one I tailored for my car only, starting with my stock tune, and if I go out and drive my car right now it runs perfectly, as it did the other day up until it malfunctioned again. I spent alot of time/miles getting it where it is and believe that if not "spot" on then it's very close. My VE's are all -1 to -5 or 6. It starts hot and cold very well with no "hunting" for idle at all and my cam surge now is only very slight at 0% TPS and only between probably 1300-1600 rpms as I'm coming up to a stop. I did the throttle blade screw adjustment with the idle relearn and it idles perfectly at 900 rpms hot. This is just something that seems to show up randomly and very suddenly. Such as a cam sensor failure, or maybe as Mark suggested bad gas with water in it or a fuel pump going out or ? It goes from running perfectly to almost literally undrivable within about 10 seconds, not what is typical of a bad tune at all.

Thanks for the responses though The wierd thing is that it didn't even throw an SES even though it was imitating a bull riding simulator. You'd think the PCM would pick up on that ? I could have some codes with no SES I guess ? I wonder what bad o2 sensors feel like ? Maybe I should throw my formerly removed rear o2's in there ? The trouble is that it's not malfunctioning now. Oh well ......

Mark, no I haven't plugged my MAF back in. The other night I was too far from home to chance pulling over for diagnostics and having it die and not restart or something. I was just trying to get it home, and now it runs perfectly again.

93TAWicked1, no I didn't have the intake off. It was just a normal cam only install, but I already checked my MAP sensor and it's plugged in correctly.

Thanks again
Bill

sardog46

Bill I would go with your plans to change the fuel filter, and when you do it, change the gas at the same time. Do you have a fuel pressure gage?

I would check those fuel problems first, and then go on to the tune. I notice those problems real bad when my filter was dirty. chnaged that and it went away.

WAHUSKER

iTrader: (4)

Thinking back to the old cars, when a fuel pump started to go, it wouldn't buck, it would just slow down at hi rpms, or die altogether. Bad gas would make it misfire horribly. As would a bad distribitor or coil.

If it was an ignition problem, you should get an SES light, or at least a code. When a coil pack or even a plug wire is disconeected you get indicators. Same with a fuel pump failure or low pressure (I think anyway). Bad gas wouldn't set any code. Neither would a plugged filter.

I'm trying to imagine what the warm sunny weather on Saturday would do, since your SD tuned car was dialed in on a cooler day. I would think you just lose power. What you describe sounds like VERY lean or ignition way before or after TDC. There is a cam position sensor wire at the back of the engine. If that came lose or got fouled with something.....did you wash / clean the engine?

maximental

Your problems remind me of the problems I had with an old '70something Buick one of my girlfriends had. It turned out that the hydraulic lifters were collapsing. It was also a very random occurence like you describe. Does your setup have hydraulic lifters? They may not be able to handle the new cam.

Just sharing a thought.

Maximental

GEARHED

iTrader: (5)

Very true - you will get NO codes if the fuel is rotten and filter is shot (I know first hand). When you first posted the ability for your car to give you whiplash then smooth out, the whole junk in the fuel line came to mind before anything else. Water is a real annoying issue and difficult to track down.

Change the filter, flip it over (clip side down) and while its dripping out take a lighter and hold it close. If it lights, no water in the line. If it barely flames, water. Check the color - any slight discoloration means you've sucked up some sediment. Easy way to rule out fuel issues, it only takes about 10 min to change out the filter.

WAHUSKER

iTrader: (4)

Good troubleshooting tips lady!!!

GEARHED

iTrader: (5)

Sometimes I actually live up to my board name

Rottluver

iTrader: (3)

I am deeply impressed.........

Oh yeah, hope you get this issue solved soon too, that sux to have unknowns.

NataSS Inc

iTrader: (9)

I am almost leaning towards a fuel clog/bad filter etc.

GEARHED

iTrader: (5)

If you don't have a fuel pressure gauge a good way to know if your fuel pump is working properly (because if it goes, you are f**ked), take the cap off the gas tank and put your ear to it while someone else starts it cold.

No sucking sound for a few seconds means the lines are clogged and your pump isn't pulling properly or is dying a slow death. Try changing the filter and blowing out the lines first - including the injectors.

92 z28

i also had a bucking issue until the car totally gave up (99 ws6). now the car will start and immediatly shut itself of. the fuel pressure gauge says the pressure is fine and stable. would any sensors cause this kind of problem? (ie cam sensor, crank sensor)

burbman

Oil pressure sensor would shut you down right away if it did not think the engine was being oiled properly.

Nate_Taufer

iTrader: (1)

i dont know about that. I had an oil pressure sensor die in my car and it drove fine. scared the **** out of me but it never shut down or drove differently.

Nate

HitmanLSX

any updates bill?

92 z28

well, the gauge in the car has a healthy oil pressure when its on for the few seconds, so wouldnt that mean the sensor is working ok?