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I have a Vortech supercharged '95 engine and 6 speed in my widened MGB and it has run great until I took it apart for a new clutch and exhaust system. Now when cruising and I give it a small amount of throttle it won't accelerate until I give it some more throttle and then it takes off. There is not a smooth transition sort of like if the accelerator pump in a carburetor wasn't working and then the main circuit suddenly kicks in. I really noticed it at freeway speeds if I start up an incline. The vacuums drops to almost zero as I give it more and more throttle before it takes hold and then accelerates past the cruising speed I want to maintain. I had the engine out of the car to replace the clutch but it started up fine and idles with normal vacuum. I get a periodic check engine light when the hesitation is happening but I don't have an OBDI reader to get the code(s). I have the 16 pin OBDII plug in that came with the 95 engine harness but my OBDII reader won't connect with the PCM.
The PCM bases the accel enrichment on throttle movement and MAF flow increase. Is it possible your connector/duct between the MAF sensor and throttle body is loose or torn, allowing air to bypass the MAF sensor? Possible the MAF sensor was damaged?
Outside thought - check the fuel pressure at idle with and without the vacuum compensation line attached to the fuel pressure regulator. Check it out on the road (vacuum line attached) while replicating the sluggish accel transition?
If you can find an OBD-1 scanner, Shoebox shows the jumpers to connect to you 16-pin connector:
Thanks for the advise, I'm looking for an OBD1 scanner but no luck so far. No apparent leaking around the MAF but still digging. How do you check the operation of the MAF? Is there a meter reading you can take on the pins?
I've been busy helping the wife get all her Christmas decorations down and set up so haven't had much time for the car. I thought I hit the jackpot when a new neighbor mentioned that he was a car guy and he had an OBD1 and 2 scanner. I followed all the directions mentioned above to hook it up to my 16 pin connector but I could not get it to connect to the computer. I tried for a couple hours but still no luck. My last resort is to take it back to the shop that tuned it for me when I first got it running and see if they can access the codes.
It was wired the same way when the shop tuned it so the connections must be right. I used the same diagrams when I wired the DLC when I was building the car. Not sure why the scanner wouldn't work.
Injuneer - I reread you idea about the fuel pressure. One of the changes to the car before the problem started was the installation of a new fabricated fuel tank. The tank has an internal pump and an external inline 100 micron fuel filter. I always thought the filter was on the small side but it always ran OK so I never gave it any more thought. I have a new paper element for a different filter so I blew through it and it had absolutely no resistance. When I tried it with the element that was in the car I could barely blow through it. I cut it apart and unfolded the paper accordion and tried blowing through a small section of it and could barely force any air through it. I now have a new (and much larger) 100 micron stainless mesh filter ordered so I will see if that makes it drive normally. Can anyone think of a code that could be generated from a plugged fuel filter?
A clogged filter will eventually cause the fuel system to be unable to maintain the fuel pressure and supply adequate fuel as engine load increases. Until it reaches that point, the primary evidence will be elevated (above 128) long term fuel trims in the low load/low RPM cells. When you exceeded the point where pressure starts to drop, you could see:
DTC 44 - bank 1 O2 sensor lean exhaust indicated
DTC 55 - lean fuel monitor. I believe that deals primarily with O2 readings being lean in power enrichment mode.
As soon as the new filter arrives I'll take it out and see if the problem is still there - hopefully it will be gone. If that doesn't work, I guess it will be a trip back to the tuner and see if he can figure it out. I'll let you know.
Best investment was a fuel pressure gauge with the longer hose. I have used it so many times to rule out low fuel pressure. Being able to drive it and watch the gauge under acceleration has saved me so much time and troubleshooting. It was $35 and has paid for itself many times over. I actually leave it hooked up and just snake it through the hood when I need to verify pressure is staying up under WOT.
Best investment was a fuel pressure gauge with the longer hose. I have used it so many times to rule out low fuel pressure. Being able to drive it and watch the gauge under acceleration has saved me so much time and troubleshooting. It was $35 and has paid for itself many times over. I actually leave it hooked up and just snake it through the hood when I need to verify pressure is staying up under WOT.
I got the new fuel filter and put it in and it seems to run better but not perfect. The bad hesitation is gone but it still isn't quite as responsive to the throttle as it was. The clogged filter was certainly an issue but not everything. I'm still going to take it to the tuner and see if he can polish up the part throttle drivability and tell me what codes the computer has in it. Full throttle still scares me as much as it always has so there don't seem to be any issues there. Thanks to everyone for their suggestions.
I have a 3 gauge pod mounted with nitrous, fuel and narrow band o2 for sale. You will need a transducer for the fuel pressure and some wiring know how. They are Autometer Phantom gauges (white face). I am looking for $300+ shipping
