growe3 Posted April 30, 2005 Report Share Posted April 30, 2005 I think I have a MAP going bad, but I am not sure. 93 STS w/4.6 Symptoms: At just off idle, when accelerating normally I get a slight buck; a little heaver throttle, and a bigger buck. Very slight surging at 30 MPH or lower, at higher speeds seems fine. WOT is fine. It is very reminiscent of a carburetor with an accelerator pump going/gone bad. Spark plugs, spark plug wires and coils are fine. I swapped wires and coil with a known good set and no change in symptoms. Plugs are fresh AC Delco 41-950. Idle normal, with slight roughness at times. No error codes have been set. FPR replaced three months ago. Checked diagnostics and the MAP seems within limits, but the symptoms seem to point at it as the problem. Any ideas or suggestions? -George Drive'em like you own 'em. - ....................04 DTS............................ Link to comment Share on other sites More sharing options...
growe3 Posted April 30, 2005 Author Report Share Posted April 30, 2005 Would I be looking for a steady pressure, at all times? What PSI ? -George Drive'em like you own 'em. - ....................04 DTS............................ Link to comment Share on other sites More sharing options...
growe3 Posted May 1, 2005 Author Report Share Posted May 1, 2005 Thanks for the information bbobynski, now I just need to find the appropriate gauge to test the system. -George Drive'em like you own 'em. - ....................04 DTS............................ Link to comment Share on other sites More sharing options...
growe3 Posted May 4, 2005 Author Report Share Posted May 4, 2005 Did you read thru this thread to the ending posts...?? http://caddyinfo.ipbhost.com/index.php?showtopic=5858 Thanks for the heads up on the home made tester, I decided to go ahead and add to my tool supply with a regular fuel pressure tester. The pressure bleed off also keeps it clean with less chance of a fire. Results: Start and idle = 37-38 PSI Just starting to apply throttle = slight dip to 36 PSI then back to 39 PSI At about 1500 RPMs = 38-39 PSI (bumped 40 PSI momentarily) 1. What do you think, is this enough pressure to operate the injectors properly? 2. Does the slight 3-4 PSI fluctuation seem normal? If I need a fuel pump so be it, but I hate to go through the cost and labor if the pressure is normal. So far I haven’t found the fuel pressure specification in the manual. -George Drive'em like you own 'em. - ....................04 DTS............................ Link to comment Share on other sites More sharing options...
BSchlossmann Posted May 4, 2005 Report Share Posted May 4, 2005 Have you de-carboned your phenolic spacers. I had to do mine at 100k miles. The symptoms I had were more of a shudder under light acceleration. The stealership wanted $350 for the procedure. You can do it yourself in a couple of hours. There's plenty of info on this subject in the archives. Link to comment Share on other sites More sharing options...
growe3 Posted May 4, 2005 Author Report Share Posted May 4, 2005 Have you de-carboned your phenolic spacers. I had to do mine at 100k miles. The symptoms I had were more of a shudder under light acceleration. The stealership wanted $350 for the procedure. You can do it yourself in a couple of hours. There's plenty of info on this subject in the archives. I did a complete head gasket repair and a thorough engine cleaning a couple of years ago. I wouldn't think there is any buildup yet. The car gets mostly high-speed freeway use. -George Drive'em like you own 'em. - ....................04 DTS............................ Link to comment Share on other sites More sharing options...
growe3 Posted May 7, 2005 Author Report Share Posted May 7, 2005 I decided to replace my fuel filter before going any farther in testing. I removed the one-year-old filter and cut it open; to see if any unusual junk was inside, nope it was just fine. When I was putting on the new filter for some reason the plastic filter holder was being a bit difficult. This caused me to get a light and look closer. With the light on I pressed the fuel filter onto the front fuel line, I then pushed on the rear fuel line. Whoa there!!! The rear fuel line was partially kinked! As everything was positioned correctly I examined closer and found that the rear fuel line was too long; so that when connected to the fuel filter it kinked the line. I disconnected the rear line, manipulated it higher toward the fuel tank, and then reconnected it. No more kink, the line still looks good. Summary: The kinked line would explain the fuel starvation feeling I was getting and the roughness when just starting to accelerate. I am not quite sure how it happened. The filter has been on for about a year, the roughness and stumble just started about two months ago, on an intermittent basis. I am guessing that I pulled the fuel line down too much when I replaced the filter last time, and that the rear fuel line was under, out of plane compression. Over time the line finally kinked. New readings below: Start and idle = 39-40 PSI Just starting to apply throttle = quick jump to 47-48 PSI then back to 40 PSI At about 1500 RPMs = 40-42 PSI Bbobynski was correct in thinking that the root of the problem was fuel pressure related. If anyone else has similar symptoms, it may pay to take a close look to be sure that your fuel lines do not have a kink(s) near the fuel filter connections. -George Drive'em like you own 'em. - ....................04 DTS............................ Link to comment Share on other sites More sharing options...
EldoradoBrian Posted May 27, 2005 Report Share Posted May 27, 2005 I just went through the EXACT same thing. It IS your MAP sensor. I had the dealer replace mine, and then car now runs GREAT. That is what it is. Brian Link to comment Share on other sites More sharing options...
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