j5 Posted April 30, 2008 Report Share Posted April 30, 2008 Ok here was a presistant problem that came up soon after I rebuilt my MPI engine and now was solved after much frustration, almost lost street races and stumbling awkward moments during a run. Please forgive me for the long post I feel I should share my insight with my brothers and sisters here. I had this high rpm stumble that occurs at 5000 rpms no matter what boost I run. For a long time I blamed the stock cam for it. But recently I went back to sds's web sight on a hunch about a vaccume ristrictor for the MAP Vac/boost signal line. Now SDS said only put a ristrictor if you can not get a stable idle. I got a stable idle so I never saw a need for this ristrictor but installed it anyway. I took Red to the nearest on ramp and floored it and she revved past 6500 without a hiccup. I guess the boost signal fluctuated quite a bit to mess up the signal enough. A few days later the car stumbled on the road and started running rough, I thought it was the fuel going bad and ethenol dropping out and turning to water I added some gas treatment the problem was still there. I was wondering if it was the sds fuel programing or timing I had the car idling when I opened the glove box to reach for the base program map I had laying around and the car died. (I keep the Main computer bolted behind the Glove box) Well it was the ground wire which was a bit short on length and was not making good contact to the chassis so when I opend the glove box it broke contact shutting the car down. Easy fix. If your MPI car stumbles and falls on its face you might have compounded problems that cost near nothing to fix. Check your grounding wires. Read the trouble shooting guide you my have missed something. Here is the car set up I'm running (someone will always ask anyway) Red 88 conquest. Punched out .040 over JE pistons TEP ARP rod bolts ARP head studs Bal elim kit from Dad's Timing kit " " Astron MPI intake CHad's I think its been awhile SDS EM 4F MSD coil packs Free 18G turbo rebuilt becase of F.O.D. You know who you are monkey scrotum! Cost $125 for new repacement comppressor wheel stock cam yes they do rev past 5000rpms but make very little power above that. stock jv head with port job stock valves stock valve springs. The 88-89 valve springs do not float (at least mine does not at 6500rpms) Estimated HP on my but dyno is 260hp but my friends say its more I don't know never dynoed it. Link to comment Share on other sites More sharing options...
macrophage Posted April 30, 2008 Report Share Posted April 30, 2008 Remember, any electronic equipment must be properly grounded not just twisting wire and wrapping it around a screw or something it needs to be soldered. The reason things burn out is because the output current needs to go to ground otherwise your FETs and MOSFETs or output transistors will over heat and burn up cause the current cant go no where. Link to comment Share on other sites More sharing options...
emagdnim Posted April 30, 2008 Report Share Posted April 30, 2008 I dont think it's the cam after 5k, I think its the small turbo.. Link to comment Share on other sites More sharing options...
importwarrior Posted April 30, 2008 Report Share Posted April 30, 2008 glad you got it all fixed. i dont think the stock cam is that bad it got the EIP car in to 10.6 in the 1/4 mile and 10.4 with a shot in first gear. Link to comment Share on other sites More sharing options...
substock Posted May 1, 2008 Report Share Posted May 1, 2008 what did you use as the restrictor for the vac? i'm having a bad idle with my ms and through reading the manual saw it said to install a restrictor Link to comment Share on other sites More sharing options...
j5 Posted May 1, 2008 Author Report Share Posted May 1, 2008 what did you use as the restrictor for the vac? i'm having a bad idle with my ms and through reading the manual saw it said to install a restrictor Checker auto or autozone will have a 3/16th vacume barb it has a brass insert in it with a small hole. Link to comment Share on other sites More sharing options...
Laodicea Posted May 1, 2008 Report Share Posted May 1, 2008 Checker auto or autozone will have a 3/16th vacume barb it has a brass insert in it with a small hole. And this is called a restrictor?? I need one...mine also stumble at 6k won't rev anymore. Link to comment Share on other sites More sharing options...
j5 Posted May 2, 2008 Author Report Share Posted May 2, 2008 And this is called a restrictor?? I need one...mine also stumble at 6k won't rev anymore. It looks like a plain jane barb on both ends with a brass thing inserted in it with a very tiny hole. Vaccume hose restrictor. Link to comment Share on other sites More sharing options...
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