chevelle3504speed Posted April 2, 2012 Report Share Posted April 2, 2012 Hey guys, I am having a hesitation issue with my '91 GTP 5 speed. I bought the car in July of 2010 with 197k on it. It now has 208k. Since I have owned this car, it has had a tip in hesitation which is temperature related. For example on a cold winter day ~20 degrees fahrenheit on a cold start, the first 2 or so minutes are very smooth and hesitation free. After about 2 minutes, the hesitation crops up and gets worse as the engine temp increases. The hesitation is at its worst at about 130 degrees. Once the engine warms up to 195, the hesitation is still noticeable, but much less so. If the outside air temp is like 40 degrees or higher, the hesitation is there right from the start, even on a cold start. I guess I should describe the hesitation. Every time you crack the throttle, the engine cuts out to an extent momentarily, causing the engine to rock back and then forward again about once; sometimes a bit violently and then it gets over it. If you roll onto the throttle extremely (and I mean extremely) gently you can just about avoid it. The engine performs fine; it's got good power and runs smoothly except for said hesitation. I have checked the fuel pressure (45psi; service manual says 40-47 is acceptable), MAP sensor values look fine. Even switched MAP sensors with another car and it made no difference. No SES light. I drove the car twice right after I bought it in July before pulling the engine to do some repair, and it had the hesitation then. While the engine was out, I replaced the timing belt and chain, bottom end, and some other things including the TPS. When I had the car running again a few months later, the hesitation still existed and had not changed a bit. I bought a 3.4 service tool kit for the thing, figuring the cam timing was off a touch. I pulled the cam gears off, bolted my homemade hold downs on the cams (service tool kit was missing the cam hold downs), etc. and put it back together. Hesitation was unchanged and still exists. Have you guys experienced anything like this before? I really like this car, but this hesitation's about to drive me wild! What should be my next move? Thanks, Andy Quote Link to comment Share on other sites More sharing options...
Night Fury Posted April 2, 2012 Report Share Posted April 2, 2012 intake air temp sensor perhaps? Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 2, 2012 Report Share Posted April 2, 2012 buildup in the intake/TB would be something easy to check out. Quote Link to comment Share on other sites More sharing options...
jman093 Posted April 3, 2012 Report Share Posted April 3, 2012 Since it seems to be ok in open loop, a bad O2 sensor is possible. Quote Link to comment Share on other sites More sharing options...
chevelle3504speed Posted April 3, 2012 Author Report Share Posted April 3, 2012 Yes, but hesitation still occurs when engine is cold as long as the outside air temp is about 40 degrees or higher. Computer is in open loop when you first start the engine, regardless of air temp. Quote Link to comment Share on other sites More sharing options...
chevelle3504speed Posted April 3, 2012 Author Report Share Posted April 3, 2012 This may take a little time to figure out. Trying to get Turerpro RT to work with the car. Haven't used it before. Quote Link to comment Share on other sites More sharing options...
chevelle3504speed Posted April 13, 2012 Author Report Share Posted April 13, 2012 Okay figured out Truner Pro RT and got data. I checked the TPS and IAT values. Both are accurate. TPS voltage and percentage increase smoothly as accelerator is depressed. I cleaned the TB as well. There was hardly any buildup in there but I figured what the hell. Where do you guys think I should go from here? Quote Link to comment Share on other sites More sharing options...
91GPLQ1 Posted April 13, 2012 Report Share Posted April 13, 2012 Injectors do not have a specific trouble code, so they almost always go under the radar. If original injectors, it may be time for replacements? Check coil resistance at injector posts, should be within some tens of an ohm. Quote Link to comment Share on other sites More sharing options...
Garrett Powered Posted April 13, 2012 Report Share Posted April 13, 2012 mine doesn't have IAT. it has MAT and IAC position. have you tried tuning the throttle follower? Quote Link to comment Share on other sites More sharing options...
redmetrix Posted April 14, 2012 Report Share Posted April 14, 2012 My 93 GTP LQ1 had some hesitation before I changed the upper and lower intake gaskets as well as changed a cracked vaccum hose located under the lower intake. Quote Link to comment Share on other sites More sharing options...
Addicted To Boost Posted April 14, 2012 Report Share Posted April 14, 2012 (edited) Check the resistance on each of your fuel injectors. The early multec injectors are common to fail when they get hot. They should all read approximately 12.2-12.4 ohms. Edited April 14, 2012 by Addicted To Boost Quote Link to comment Share on other sites More sharing options...
chevelle3504speed Posted April 18, 2012 Author Report Share Posted April 18, 2012 I changed the intake gaskets on it when the engine was out a year and a half ago. The car idles fine, so I don't think it's a vacuum leak issue. I have not fooled with tuning the throttle follower. Thanks for the info on the injectors. I will check the resistance. Previous owner said he had them replaced, but who knows. I drove the car up to the Spring Rod Run in Pigeon Forge, TN this past weekend. I had not been to that event before. Lots of cool cars, but I was surprised at the number of jacked up 3/4 and 1 ton diesel trucks with rebel flags hanging off the back cruising the strip. That event is fun but rednecky as hell, and keep in mind I live in AL! Anyway, to get to the point, my SES light came on on the trip, and when I jumper the ALDL connector, SES light flashes code 39. I could not find a code 39 listed in the service manual. After looking in the manual, I went checked the code again and confirmed that it is 39. Anybody else had this happen? Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted April 18, 2012 Report Share Posted April 18, 2012 39 is the DTC for the clutch switch. Quote Link to comment Share on other sites More sharing options...
Garrett Powered Posted April 18, 2012 Report Share Posted April 18, 2012 my 5 speed throws a ses light after I drive it around and idles kind of weak. I am slowly tuning the idle to be stronger but not too strong since I like to ride 2nd as I downshift. but the IAC is the what I look at in datalogs and dips in voltage. heavy electrical loads like when the fan kicks on. even the vent motor will pull down on it. I tuned the throttle follower good enough that it doesn't stall going into the idle cell pulling up to stops. brake lights pull on the motor even. I got an aluminium flywheel making it worse and a cs144 so that is different than stock too. but the fan settings are very useful for adding IAC steps where necessary and I still need to do this on my 5 speed. did that on my black TGP and it worked great! still need to tune the red TGP. that car hesitates bad still but its sitting uninsured right now. Quote Link to comment Share on other sites More sharing options...
chevelle3504speed Posted April 19, 2012 Author Report Share Posted April 19, 2012 The clutch interlock switch? Quote Link to comment Share on other sites More sharing options...
chevelle3504speed Posted November 30, 2012 Author Report Share Posted November 30, 2012 Update: Injectors are fine. My hesitation was absolutely a cam timing issue. I went back and timed it yet again (3rd time) with a 3.4 adjustable cam tool (set at 0) and it pretty much cleared it up. I am going to go back and tweak it and try and get rid of it completely. Man, you have to get that timing absolutely, and I mean absolutely dead on to avoid the hesitation. I had a '95 Z34 Monte Carlo and it definitely was not as picky about the cam timing as my '91 3.4 is. Maybe cause the '95 has a cam sensor? Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted November 30, 2012 Report Share Posted November 30, 2012 the cam sensor(in the 94-95 at least) is only used for injector sequencing. it doesn't modify anything based on it. could it be that the 94-95 cam sprockets are different than the 91-93 versions? Quote Link to comment Share on other sites More sharing options...
chevelle3504speed Posted December 3, 2012 Author Report Share Posted December 3, 2012 The 91-93 models have lock rings that hold them in position. 94-95 have a tapered washer that hold the cam gears in position. That is the only difference as far as I know. The teeth on the tears are the same. I have 95 gears on my 91 3.4. The teeth are different on the 96-97 models I believe. Quote Link to comment Share on other sites More sharing options...
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