PimpWillis

iTrader: (1)

I recently threw together a 355 HSR with Trickflow heads and the XFI 268 cam, but am having some problems when I'm trying to actually just cruise. It's having these major bucking or jerking issues when I'm not giving it much gas, just enough to maintain speed. It does it mostly when the engine is warm no matter what speed I am going. I have pretty good idle, by good I mean it's happy at about 1000 RPMs and fluctuates maybe a 100 or so. Though maybe you guru's on the board might be able to point me to a fix. I have performed the TPS/IAC setting procedures and tried looking for a vacuum leak with no avail. Any tips or comments would be greatly appreciated.

Orr89RocZ

iTrader: (20)

Its probably just the tune. What are you doing to tune this car? Fuel and timing may be off.

scamaro355

PimpWillis

iTrader: (1)

I know it's the best thing, but I got a "tune" from Harris performance thinking he could get me into the ballpark of where I need to be. I heard that cam is easily tuned so I figured I would start with a generic tune then try and learn to do it myself. I was really hoping the bucking would be something I knew how to fix, but maybe I will have to learn. If I happen to get some burning tools what should be the first thing to look at?

scamaro355

https://www.thirdgen.org/forums/diy-prom/

Orr89RocZ

iTrader: (20)

Heres a quick thing to try... Whats your current base timing? If its 6-8 like factory, set base timing 2-4 deg lower and see if it does it again. Then try 2-4 deg higher and see if it does it.

If the air fuel is off, it will have issues down low rpm like that. Timing will sometimes mask the problem and backing off abit may help.

If you have a stock chip, try that too. But i'd buy the equipment to tune and start with a modded ARAP bin with different timing table for now. Its a decent starting point and should run fine without too many changes.

Ofcourse, there always can be some other issue causing this problem. Check all the mechanical stuff and once you confirm the motor is together right, then look at the tune.

PimpWillis

iTrader: (1)

I'm trying to beat the inevitable right now I know, but base timing is at 10* ill give lowering it a try can't hurt. I was also wondering if the pickup coil inside the distributor could cause something like this. Its the one thing I haven't changed on the car since I bought it in 2002. Thanks for the help I appreciate it

scamaro355

if there was a problem with the pick-up coil most likely it wouldnt run at all

Looksthakill

Hey Willis, did you ever figure this out?

PimpWillis

iTrader: (1)

Unfurtunately I haven't. I moved from Jersey to Florida recently, (brought the Iroc of course) and haven't had the chance to play around with it. I really need to get a datalog cable and see what is going on when the problem happens. Like everyone told me, it's more than likely something in the tune. At least I hope anyway.

palric

iTrader: (1)

I think you have something else going on and not your 'tune'

I had same problem with stock cam and chip. Been hunting it down for way too long. I have replaced just about everything (car is 20 years old so I figured ynot?).

That includes all sensors and the pigtail connectors, coil, ign module, plugs, wires. Name something I have not replaced. Hmmm... I have not replaced the fuel tank and fuel pump. Did do injectors and afpr though...

I had it out today and after it warmed up did it again. It is like the engine dies as in lights out, cut off 2500 rpms to zero rpms then starts up again in less than a second. while this happens i get whiplash...

I disconnected and blocked off every vacuum connection on the engine. Car still ran however bucking continued

I thought it might be electrical so mounted a few zero guage ground wires

I figure I will swap to an LS setup. Maybe that will fix the problem?

Looksthakill

I am thinking that it may be one of these culprits on my car, but I have not tested any of them yet. Just a guess. Let me know what you guys think:
1. Adjustable fuel pressure regulator. I have the Holley HSR AFPR. I have heard bad things about them.
2. O2 Sensor.
2. Possible ignition problem.
3. Fuel injector(s)?

All of these components are new (past year), but I am STILL having this interim problem. Any advise guys?

anesthes

iTrader: (12)

Sounds more like just not enough cruise advance.

I've had bucking problems before trying to walk across a parking lot and ultimately that's just asking too much out of a big cam, but when we're talking bucking at cruise it's usually a fuel or timing issue, or both. For lean cruise you want a lot of advance. I run 38-40* degrees in my lean cruise, which will be around 15-16:1 AFR. Remember - this is CRUISE.

-- Joe

PimpWillis

iTrader: (1)

I honestly think for my application, spending $60 on a ALDL cable to see if it's as simple (or not) as a tune, is much better than replacing parts that don't need to be. I figured that after I spend a whole afternoon replacing a fuel pump that didn't need to be, which probably took 5 years off my life from the aggravation. I'm still settling into my new place still, so the Iroc is on the back burner for just a wee bit longer.