ScoobyDoo82 Posted October 23, 2010 Report Share Posted October 23, 2010 I was just wondering, what all can be caused by a bad vacuum modulator. My 88 GP has the hard shifting into reverse when it warms up, and it hesistates and stumbles sometimes when I accelerate. There are a few other quirks, but I was just wondering what all can be cause if it goes bad. Quote Link to comment Share on other sites More sharing options...
Schurkey Posted October 28, 2010 Report Share Posted October 28, 2010 the typical result of a bad modulator is: 1. shifts go higher in rpm, and much more firm (harsh) for awhile, then 2. transmission won't go into gear at all, or slips terribly due to low fluid level. Quote Link to comment Share on other sites More sharing options...
bronze93 Posted October 28, 2010 Report Share Posted October 28, 2010 AS long as you are talking vacuum modulators, is there supposed to be a check valve in the soft hose between the modulator and the hard line? Quote Link to comment Share on other sites More sharing options...
Schurkey Posted October 28, 2010 Report Share Posted October 28, 2010 Of course not. A check valve would interfere with the modulator being able to sense the vacuum in the intake manifold. Either the vacuum couldn't get to the modulator, or the vacuum wouldn't be released from the modulator. Quote Link to comment Share on other sites More sharing options...
bronze93 Posted October 28, 2010 Report Share Posted October 28, 2010 I wonder why there is one in mine? PO must have put it in but why? Quote Link to comment Share on other sites More sharing options...
94vertluvr Posted October 29, 2010 Report Share Posted October 29, 2010 My 94 Olds had the hard shift but the vacuum modulator was not even plugged in...the shift improved but is still a little hard. I'm also experiencing the hesitation and stumbling upon acceleration...I'm thinking maybe due to bad ignition coil but not really sure so I guess I'm kind of in the same boat. I was just wondering, what all can be caused by a bad vacuum modulator. My 88 GP has the hard shifting into reverse when it warms up, and it hesistates and stumbles sometimes when I accelerate. There are a few other quirks, but I was just wondering what all can be cause if it goes bad. Quote Link to comment Share on other sites More sharing options...
ScoobyDoo82 Posted October 29, 2010 Author Report Share Posted October 29, 2010 Well i replaced the module. The hesitation isnt quite as bad anymore but its still there. So I wouldnt say its completely vacuum related. A few days ago I started it up and it ran like crap and shot code 42... but I shut it off and restarted it and it didnt do anything so I dunno. Plus my coolant light likes to come on at random times even though theres plenty of coolant in it. Mine definately has a few quirks Quote Link to comment Share on other sites More sharing options...
94vertluvr Posted October 29, 2010 Report Share Posted October 29, 2010 A couple things i'm looking at with mine are coils/ignition, Oxygen sensor and throttle position sensor. Mine is not throwing any code or any SES light so I'm kind of in the dark. As for the coolant I did fix that problem in mine last week; my light kept coming on too even though it was showing full; I decided to do a flush/fill and the stuff was nasty looking that I drained out! Put in new coolant and ever since no light has come on!!!:thumbsup:Lemme know if you come up with a solution for your car. Mines a 94 3.4L. Quote Link to comment Share on other sites More sharing options...
chrisflstf Posted October 29, 2010 Report Share Posted October 29, 2010 I had a shifting issue similiar to Scoobydoo and thought it was the vac mod - it wasnt. Couple months later I replaced the upper intake manifold and LIM gaskets. Now the shifting issue is gone, so I had a vacuum leak in the UIM causing my shifting problem For your coolant level issue - it sounds like you have air in your system. Get the car up to temp, with the heater WIDE open and blip the throttle up to 2000 RPM for about 5-10 seconds, let go, and watch for bubbles in the reservoir. That procedure works well to purge air. Quote Link to comment Share on other sites More sharing options...
ScoobyDoo82 Posted October 31, 2010 Author Report Share Posted October 31, 2010 A couple things i'm looking at with mine are coils/ignition, Oxygen sensor and throttle position sensor. Mine is not throwing any code or any SES light so I'm kind of in the dark. As for the coolant I did fix that problem in mine last week; my light kept coming on too even though it was showing full; I decided to do a flush/fill and the stuff was nasty looking that I drained out! Put in new coolant and ever since no light has come on!!!:thumbsup:Lemme know if you come up with a solution for your car. Mines a 94 3.4L. A follow up on that is... I just took it to the car wash the other day and it started running like crap and missing badly... I'm thinking coils too, or bad wires. We'll see. Quote Link to comment Share on other sites More sharing options...
94vertluvr Posted November 1, 2010 Report Share Posted November 1, 2010 I've read something about water getting into something and causing this...do a search and see what you come up with on it...I know I've seen it recently! Quote Link to comment Share on other sites More sharing options...
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