This has been a problem ever since I rebuilt and installed my turbo kit. My mods are as follow: Hahn kit with sidemount, vortech 12:1 fmu, missing link, wiseco pistons, eagle rods. If run the car hard through the gears it will not hesistate, only occusionally. If I go throug first and second slowly, then go into third and floor it it will hesistate and buck. it will also do this in 4th and 5th. If I attept to go full throttle on the highway it will hesitate as well. It used to do this with the black box so I got the missing link and it helped but its still there. I have checked all the obvious, spark, wires, coil, o2 sensor. I have gotten a lean code as well as a map sensor code. Earlier tonight I was looking at my a/f and when I when wot in 5th my a/f was at .48 and it detonated/hesitated. Is this a map sensor issue, or is the missing link not doing it's job, it seems like it hesistates once it starts going into boost at wot in 3rd 4th and 5th. If anyone has any ideas please let me know, thanks. By the way I have learned everything off of this board it's amazing, but I am stumped now.

What are your fuel settings? And do you have the plugs gapped approprietly?

Wow, from reading your post, it seems you are running very lean (be careful!) Do you have any kind of fuel pressure gauge??? I'm interested as to what your fuel pressure is under boost. You might want to hook up the HRC fuel pressure gauge and try to set your fuel pressure per HRC's original instruction (since that gauge can't be mounted inside the car.) What about an egt gauge? Got one? Unless there's seriously something wrong with your O2, .48V is waaaay low. Anything less than a .87-.89 is LEAN.

Do you have an upgraded intank fuel pump, or do you have the HRC inline pump? I think you problem is fuel related, and not necessarily, the MAP issue at this point. If I were you, I wouldn't go into boost until the problem is solved.

I got the one range colder ngk plugs which where pre gapped and I checked them, I melted me fp guage on my manifold one day so I don't have one right now, or an egt guage which I am planning to get soon. I am running the hrc inline pump. It almost seems like my a/f reading stayed in open loop for a second when I go wot, but it always hesistates and I let off and don't get a chance to see if it will go up or not. thats the lowest it has hit though. I don't see what the cause of this problem is. I have been trying to keep out of boost, but it too hard. Anyone have any ideas? thanks for the replies. I saw in an earlier post that the load on the engine is greatest at the described times, around 3-4k in 4th and 5th could this be an njector problem? I still have stock injectors.

Another thing, if I go into boost gradually it will not hesitate, if start going up in rpms then get to about 4500 or so and go full throttle the problem doesn't exist, it only happens when i mash the gas. Sometimes I will got wot, build boost fine then all of a sudden it hesitates while the a/f ratio is reading rich at around .96 or so. Could it be dumping too much fuel when I try to go wot? And if it was lean wouldn't it happen in 1st ans 2nd as well? Also, if my map was to see boost would it not have the same effect and give me fuel cut, which would explain the low a/f readings at the point when the hesitation occurs?

do you have the vortech fmu or SFMU???

when i was researching the replacement for the cartech, i've wondered if i could use the fmu cause it was cheaper than the sfmu. someone replied that you can't use the fmu with the hahn kit.

also, get an in car fuel pressure gauge so that you can base your tuning from there, or else your just tuning blindly.

i find it ironic that you have a built motor yet, no fuel pressure gauge or egt?

-------jezreel
hrc stage 1, sfmu, ml, prokits, egt, boost gauge, apexi tt, costum dp, dynotune fp gauge. gst muff, turbo spoiler

nothing like driving with the windows down and the music low: i love hearing the turbo spool, swwwhhhttt!!!!
thanks for www.kaptainmyke.com for the sig hosting :thumbsup

I am using the vortech 12:1 FMU with my stock fpr for the idle fp. I ran out of money to get the egt and I melted my fp guage. You guys think a bad ground going to my battery could cause this problem. My battery cables are kinda loose, I need to fix that.

I had this problem. It was the fpr. I never had a bleed valve on my cartech. I switched over to sfmu with the bleed valve and now I run way rich sometimes and starts to misfire. But I'm putting money on the fpr.

Anyone have any other ideas?

A couple ?'s coming from a newcomer. What is the fpr, fmu , and what is detonation?

Safedawg, I reread your post and noticed you have the stock fpr AND the fmu. I think that's where the problem is. You have to remove the stock fpr, otherwise you'd choke the engine with too much fuel--especially during low boost transitions. Instead of having a fix fpr rate, you might want to consider a boost proportional fpr. That way fuel pressure is increased by a ratio (9:1, 4:1, etc) that is proportional to the boost level.

Originally posted by 95redesi
A couple ?'s coming from a newcomer. What is the fpr, fmu , and what is detonation?

fuel pressure regulator = fpr

www.misterfixit.com/deton.htm

What is it that makes this different then a star setup with the vortech and the stock fpr. Isn't it the same idea. I had the cartech, and I still have it but it weas startin to just not do its job. Onw more question, does the stock fpr have a vac source or not?

i would bet if you remove the stock fpr it would clear your problems up, cuz after the fuel goes through the fmu it wants a nice unrestricted return to the tank, if you build pressure up after the fmu that will force the plate in the fmu back up therefore pretty much making the fmu useless, anyway i think that is what would happen, either way the stock fpr should not be there.

Mods:
CAI, OBX exhaust, Grillcraft grills, altezzas, ard ryver g6 17's wrapped w/ falken's, VIS racing c.f hood, 2 12" kicker comp's w/pioneer h.u, streetglow blue undercars, red dash kit, indiglo guages, n other shit

If I remove the stock fpr the car won't start, I need something to control the idle fp. I have plans to get the sfmu or the new CF unit, but for now I don't think I can remove the stock fpr because I have jsut a rising rate fpr. Is this right?

If you need the stock fpr, in addition to the Vortech, then there's probably another problem. Your car should idle just fine with the fmu alone.

I am having the same problem with my car. At WOT ir runs damn good, but at low RPMs it just hesitates and it rocks back and forth. This happens through all gears. I cannot cruise at all cause the car runs like crap at low RPMs. My problem is too much fuel being dumped at once. My wideband can only read above 10 and it never reads above that number. I am running way too rich. I am also running the FMU with the walbro 255lph HP. :cheers

I can cruise fine and boost fine, its just right as I go into boost at certain situations it hesitates, but if I ease it in and then go wot it's fine. I am leaning towards an either a sensor issue, or the fmu and injectors something fuel related. I think the 12:1 disc it bogging me down when I give it too much gas at once. Has anyone tried a 10:1 disc in the FMU. I hit over 1.xxx when It boosts and I go wot. Could this be my problem. Since it it putting out a 12:1 consistently instead of gradually increasing fuel with boost?

I'm running a stock FPR and a 12:1 on the Vortech FMU and I run okay in low boost/ no boost...hmmm
Alvin

96 RST

Star Stage I turbo kit /Starion I/C w/ 2" chrome piping / GReddy Type-S BOV / Missing Link / Custom APEXi- GReddy 2.5" exhaust / 55mm ARD TB/ Nology wires / APEXi EL mech boost gauge / Autometer A/F gauge / Southland Dual Friction clutch

Sounds like your fpr is reacting very slowly for some reason. Do you have an upgraded fuel pump?

edit:

Also make sure your fpr has a good vac signal, not something T'ed of something else. Not having enough throughput in the vac line to the vortech fpr could cause it to react slowly.

I am using the stock pump with the hrc inline pump. I'm gonan recheck all my connections, but I have redone it a bunch of times thinking thats what it was. It does seem as though everything reacts kind of slow. When I shift it takes a few seconds for it to cycle beck to higher a/f number, it'll stay a second at .11 or so then start going up, its not instant sometimes. Is this an o2 sensor problem? Its the bosch one a few months old.