NOTMYGP Posted October 15, 2011 Report Share Posted October 15, 2011 (edited) Hello everyone! Looking for some information, and advice. I bought my stepson a 93 GP 3.1V6/TH125 automatic with a bad trans, undriveable. I replaced the trans. with a junkyard tranny, which seems to be working o.k. The problem I'm having is I'm getting a 45 diagnostic code (O2 sensor detecting a rich condition), now I don't want to start throwing new parts at it so I was hoping I could list some other symptoms, and maybe somebody can steer me in the right direction. First of all the car starts right up, and runs only slightly rough, until the check engine light comes on, at which point it smooths out nicely. Also at this point, the exhaust starts to smell odd, but not excessively rich or anything. As it warms, it loses power,and runs rough again, I can hold the throttle steady, and the RPMs will drop slightly,no matter how much the throttle is open, it will still drop. The temp gauge doesn't work, it will go from reading high to zero when the key is turned, but never goes up from zero. Is the sending unit tied into the ECM? I know some of the potential problems that can cause a code 45 are: high fuel pressure, possibly a bad fuel pressure regulator, leaking injector(s), O2 sensor contaminated, possibly from RTV, or coolant (no leaks detected, as in no oil in coolant, or vice versa), or MAF sensor. Any ideas? I'm can borrow a fuel pressure gauge to check pressure, I checked to see if the vacuum line attached had any gas on it from a leak, none. I can't check injector balance, as I read, because I can't get at all the injectors without disassembly. Any help will be greatly appreciated, this is a low dollar project, so I'm hoping for a definite cause. Thanks in advance! Edited October 15, 2011 by NOTMYGP Quote Link to comment Share on other sites More sharing options...
virtuetovice Posted October 15, 2011 Report Share Posted October 15, 2011 Fuel pressure would be a good start, FPR would make sense. Quote Link to comment Share on other sites More sharing options...
alec_b Posted October 15, 2011 Report Share Posted October 15, 2011 I'd suspect a bad coolant temp sensor, or a stuck t-stat not allowing the engine to warm up. Never goes into open loop, runs too rich. Makes the whole thing run wacky. Could have a contaminated O2 at this point, but it's probably never been changed to it's due. Early 3.1's are notorious for leaky injectors. This could cause a rough idle/hard start for a few seconds, because of the excess fuel during startup. Would be more noticeable at warmer engine temps. I've seen bad ECM's cause these symptoms. Make sure you have good block grounds. Sounds weird, I know, but I just had an issue eerily like this with our '94 TBI chevy tow truck at work. I was getting really wacky O2 readings from the computer, just didn't make any sense. I also could never get the truck to hit closed loop. The fix was two-fold. One was someone had drilled too large of a hole in the t-stat. Who I have no idea. That was causing the truck to run MUCH to cool (barely 150 degrees). The second was a poor block to ECM ground connection. The truck used two sensor and ECM grounds, both attached to the top of the intake. One was fine, the other had almost 700 OHM's of resistance! I ran a fresh ground directly from the battery to this ground, removing the engine from the equation, and it solved the rest of my issues with the O2 readings. Quote Link to comment Share on other sites More sharing options...
virtuetovice Posted October 16, 2011 Report Share Posted October 16, 2011 alec brings up a good point. Coolant temp sensors can cause some weird problems! By now, as mentioned, the oxygen sensor is probably long overdue. DO NOT use any brand other than Denso or AC Delco. Denso is cheaper but you're getting the same thing since Denso manufactures AC Delco's sensor, from what I understand. I had to special order mine but it was well worth it. Quote Link to comment Share on other sites More sharing options...
NOTMYGP Posted October 16, 2011 Author Report Share Posted October 16, 2011 Thanks guys. I think I'll start by testing fuel pressure, if that checks out ok, I'll go with a temp. sensor, and O2 sensor, and see what happens. Not a big expense. Quote Link to comment Share on other sites More sharing options...
Schurkey Posted October 17, 2011 Report Share Posted October 17, 2011 Avoiding Shotgun Repairs = Connect a scan tool. Quote Link to comment Share on other sites More sharing options...
NOTMYGP Posted October 17, 2011 Author Report Share Posted October 17, 2011 Avoiding Shotgun Repairs = Connect a scan tool. Which do you recommend? The only one I ever used was for OBDII, and only showed, or cleared codes, didn't pinpoint the problem. Quote Link to comment Share on other sites More sharing options...
Schurkey Posted October 17, 2011 Report Share Posted October 17, 2011 (edited) Which do you recommend? The only one I ever used was for OBDII, and only showed, or cleared codes, didn't pinpoint the problem. That's a code reader, not a scan tool. I use a Snap-On "red brick" scanner. I bought 'em from eBay. The scanners are dirt-cheap because they're obsolete for new-vehicle use; pros have been dumping them for years in favor of "latest and greatest". For folks like us that work on older cars, they're perfect--and "professional grade" for older vehicles--not consumer-grade junk. The only real issue is to make sure you're buying one with the proper cables and software cartridges capable of reading the vehicles we own. My primary unit is an MTG-2500; same as the more-common MT-2500 but with a two-channel Graphing capacity. I bought a second MT-2500 because it had a later software cartridge than my other one; and some cables for Jap cars. I've now got a spare scanner and cartridge to about 2000 model year, and a small assortment of cables and keys. Check eBay, local pawn shops...or send me a pm. An OTC Genysis is also a very popular tool, but I've got zero experience with them. Same deal--get one new enough to read the vehicles you own. Edited October 17, 2011 by Schurkey Quote Link to comment Share on other sites More sharing options...
NOTMYGP Posted November 19, 2011 Author Report Share Posted November 19, 2011 Back again. I've replaced the temp sensor for the gauge(still doesn't work), new thermostat, checked the fuel pressure at the rail (42psi), checked the injectors for leaks.....none, cleaned the injectors, and replaced all the "o" rings for the injectors, regulator, and rails, new o2 sensor. The car starts immediately, runs quiet, and fairly smooth, I can drive about 1-2 miles, and it loses power, until the check engine light comes on and then it runs fine, and pulls well. I check the code, and it's still a code 45 (rich condition). I don't have access to an OBD1 scan tool, nor do I want to invest the money, even for a used one,all for a $500. car, I'll never use it again. Any other suggestions? Quote Link to comment Share on other sites More sharing options...
Crazy K Posted November 20, 2011 Report Share Posted November 20, 2011 Coolant Temperature Sensor: In a 3.1mpfi there are TWO sensors. the first is in the intake manifold. The second is on the driver's side rear corner of the head on a 3.1mpfi. CTS in intake: feeds info to the PCM/ECM, controls the fans. the fans are controlled by the ECM/PCM based on the temperature that sensor detects, and the settings that the computer is set to. CTS in head: feeds info to the instrument cluster, and there can by two versions of that sensor based on whether the car is equipped with an actual gauge or not. Did you get the correct sensor replaced, and is it the correct style of sensor? and have you verified if the thermostat is good??? Quote Link to comment Share on other sites More sharing options...
NOTMYGP Posted November 20, 2011 Author Report Share Posted November 20, 2011 The one I changed is in the thermostat housing, and is exactly the same as the old one. I don't see any other CTS on either head. The thermostat is good. I'm more concerned with the way it is running, or the presence of the code 45 than anything right now. Quote Link to comment Share on other sites More sharing options...
Crazy K Posted November 20, 2011 Report Share Posted November 20, 2011 so you changes the wrong one and don't care??? look for a single green wire on the driver's side corner of the rear head. Quote Link to comment Share on other sites More sharing options...
Galaxie500XL Posted November 21, 2011 Report Share Posted November 21, 2011 I have an Actron CP-9110 I use...paid $50.00 for it on Ebay several years ago. Not fancy, but it will get the job done. Which do you recommend? The only one I ever used was for OBDII, and only showed, or cleared codes, didn't pinpoint the problem. Quote Link to comment Share on other sites More sharing options...
White93z34 Posted November 21, 2011 Report Share Posted November 21, 2011 these o2 sensors are cheap (~$20) and are general maintenance anyhow, so pickup a good one (I like NTK or Denso) then you know that much is up to date. As Ken said, the gauge sending unit is a single green wire off the rear cyl head near the EGR IIRC, also a cheap item. Rent a fuel pressure gauge and see what it reads with KOEO (key on ignition off) and while running, might be a good time to replace fuel filter as well. Your car has no MAF sensor, make sure the electrical connection to the MAP sensor on the back of the intake plenum is good though. May be a good idea to pull the upper intake plenum to check the injector ohm ratings out, The older these get the more issues they seem to be causing for people here. I *think* Ken had a way to check the injector resistance without pulling the plenum. He may be able to expand on that. But ideally you don't want anything under 12ohms at KOEO does the Service Engine Soon lamp stay on till you start the car? if not you may have ECM problems Longshot but maybe bad coils/ICM? if you have a timing light put that on and see how strong the light is as you move the inductor from wire to wire. Quote Link to comment Share on other sites More sharing options...
NOTMYGP Posted November 21, 2011 Author Report Share Posted November 21, 2011 so you changes the wrong one and don't care??? look for a single green wire on the driver's side corner of the rear head. the point I was trying to make is the gauge functioning is of less importance to me than the way the car is running. Quote Link to comment Share on other sites More sharing options...
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