tcristea Posted March 17, 2006 Report Share Posted March 17, 2006 I just got this 90 TGP and the guy has one of Jeff M's top gun 160 chips in it. He lets the car sit for a few years and starts it up and it runs like a beat up granny. No butt to it at all and it stalls...all the time...and eats fuel like you cant imagine. Three diff mechanics look at it and tell me the engine is as tight as a new one but something has it clogged or the programming on the chip is bad or blah blah blah... I do a little checking and probing of my own and find the MAP sensor is returning 2.1 volts to the ECM. Now from what I know the voltage returned is what tells the ECM what altitude your car sits at (ie. Low altitude=High pressure=High voltage) So I'm thinking at this point that 2.1 volts is awful low for a 5 volt input so that would mean low voltage=low pressure=high altitude. The problem is I live at 750 ft above sea level. So I do a little more searching and find that the range in voltage to the ECM is from 2.5 to 5.2 volts and 5.2 is pretty much where this one should be. So enough rambling and on to the question you say??? Fair enough I say! My question is what could possibly bring this MAP to drop to 2.1 volts and make the ECM think I'm tooling around the country side atop of Mt. Everest???? :shock: I replaced the MAP, the ECM and even the wiring to and from them to rule out a bad ground. From what I have read and heard Jeffs chip is the shit and has fixed many a problems so that couldn't possibly be it?? The car is at this point a giant paper weight with wheels and driving me crazy. I am throwing myself at the mercy of the TGP GODS begging for anything that could help me on this one. :oops: Quote Link to comment Share on other sites More sharing options...
Guest TurboSedan Posted March 17, 2006 Report Share Posted March 17, 2006 MAP sensor isn't for sensing altitude at all. it senses vacuum and in the case of a 2-bar MAP sensor like the TGP uses, it senses pressure in the intake manifold as well. low MAP voltage is vacuum and high MAP voltage is boost etc. i'm not sure off hand what the voltage should be with key-on-engine-off. first thing i would do is check the crossover pipe. a cracked crossover pipe (very common on these cars) would make the engine run way too rich and run like crap. Quote Link to comment Share on other sites More sharing options...
skalor Posted March 17, 2006 Report Share Posted March 17, 2006 The map voltage actually looks fine to me. It's a two bar map sensor and the lower the voltage the less pressure you are seeing. So with the key on/engine off you will read atmospheric pressure. At ~2.5v you should be at see level and since you are 750 above sea level I would expect the sensor to read a little lower. I expect you probably have the regular TGP ailments...leaky injectors and a bad crossover. Quote Link to comment Share on other sites More sharing options...
tcristea Posted March 17, 2006 Author Report Share Posted March 17, 2006 OK...so how can I check for a leaky crossover??? Quote Link to comment Share on other sites More sharing options...
god910 Posted March 17, 2006 Report Share Posted March 17, 2006 OK...so how can I check for a leaky crossover??? First, Blow into the tailpipe and see if your breath comes out between the turbo and the engine. Let me put it this way... If it's stock, it's bad. There's no smoke and mirrors to it, they are horrible. Of course both my TGP's have Jeff's X-over, so no worries. Quote Link to comment Share on other sites More sharing options...
tcristea Posted March 17, 2006 Author Report Share Posted March 17, 2006 I love the car and all....but I will NOT blow it So basically what your are saying is there is no way to check this to avoid spending more money just replace it and hope that's what it is? Quote Link to comment Share on other sites More sharing options...
TGPilot Posted March 17, 2006 Report Share Posted March 17, 2006 SKALOR...What are you talking about? MAP Load Variable at 2.5v is normal at Key-ON?? :shock: A MAP voltage of 2.1V is the break-over between Vacuum and Boost. That is where the Chip turns over the control to the chip's PE tables. You have a bad MAP sensor if you are reading 2.1V at idle or especially at just Key On! Key on should show between .31V and .53V (.53V is 6908' above sea-level on GM MAP sensor ) at key on depending on how old, who made the MAP sensor, and your altitude. Does the MAP sensor read higher than 2.1V when you have your foot in the throttle while driving? Does the 02 sensor show open or closed loop? Better yet if you have TunerPro RT send me your recorded log and I will look at it. I do not visit here much anymore unless I hear of a post like this. I am at http://www.tgpforums.com have a look. 8) Quote Link to comment Share on other sites More sharing options...
tcristea Posted March 17, 2006 Author Report Share Posted March 17, 2006 I replaced the O2 and the MAP both and the ECM for that matter all at the same time. I used the Delco parts per what I have seen here from you guys. The reading from the MAP goes from 2.1 to 2.3 which by the looks of the table is telling the system that the car sits at above 10000 ft. The reading SHOULD be between 3.6 and 5.2 from what I can tell. I even thought there was a bad ground so I ran wires direct and it didnt change. I'll also head over to the tgpforums and check it out too. Thanks! Quote Link to comment Share on other sites More sharing options...
TGPilot Posted March 17, 2006 Report Share Posted March 17, 2006 What software are you using for logging? Quote Link to comment Share on other sites More sharing options...
tcristea Posted March 17, 2006 Author Report Share Posted March 17, 2006 I'm not right yet because I dont have the cables for it yet but I do have TunerPro. Quote Link to comment Share on other sites More sharing options...
TGPilot Posted March 17, 2006 Report Share Posted March 17, 2006 So how is it that you know what the MAP voltages are? Quote Link to comment Share on other sites More sharing options...
tcristea Posted March 17, 2006 Author Report Share Posted March 17, 2006 Took it to a friends (mechanic) and hooked it up to his stuff. Ran through all the diags for the "incomplete" 90 Grand Prix SE Turbo and got the readings from that. And a trusty Voltmeter just to double check Quote Link to comment Share on other sites More sharing options...
Pontiac6KSTEAWD Posted March 17, 2006 Report Share Posted March 17, 2006 To me it sounds like you have bad injectors. But befor we even start on that, lets clear all the dumb questions out of the way .. Have you performed a COMPLETE tune up. PLugs, wires, fuel filter, and checked for the proper fuel pressure at the fuel rail? If fuel pressure is low, replace fuel pump. You would be surprised at how many problems these fix on these cars.. Also, since you said it sat for awhile, does it have good premium fuel in it? Once thats ruled out, then I would start down the rest of the road here. Starting with the fuel injectors. You have to OHM test every one. Someone mentioned about bank ohm testing them, but I have no idea how to do that.. Quote Link to comment Share on other sites More sharing options...
tcristea Posted March 17, 2006 Author Report Share Posted March 17, 2006 A complete tuneup was performed the day I bought it (plugs, wires, feul filter, pump was replaced the week before I got it and pressure is perfect, drained the can and filled it with the $3.00/gal good stuff...DAMN, had the injectors tested and replaced the altenator, had the vacuum hoses blown out and replaced the ones that looked worn etc...) and to me there is no such thing as a "dumb question" because the obvious is not always the first choice . I also checked the grounding on almost every component under the hood to verify the connections were clean and clear since a bad ground COULD cause a drain on the volts and they were all good (went ahead and wire brushed and cleaned them anyway just to make sure). One thing to note is that when I get it on the highway and punch it I get a strong jerk and then nothing like it wants to launch but just cant. The turbo whirls like it should and the gauges all bounce like they are supposed to as well. The mechanic friend I mentioned earlier said the turbo was tight and working great and there was no oil anywhere it shouldnt be so we ruled that out as well. With all that said, PLEASE ask me some more questions because I think you guys have an awsome bank of knowledge that I hope to tap into and get this honey running like it should. And THANKS for all the quick replys....you guys are great! Quote Link to comment Share on other sites More sharing options...
skalor Posted March 17, 2006 Report Share Posted March 17, 2006 SKALOR...What are you talking about? MAP Load Variable at 2.5v is normal at Key-ON?? :shock: A MAP voltage of 2.1V is the break-over between Vacuum and Boost. That is where the Chip turns over the control to the chip's PE tables. You have a bad MAP sensor if you are reading 2.1V at idle or especially at just Key On! Key on should show between .31V and .53V (.53V is 6908' above sea-level on GM MAP sensor ) at key on depending on how old, who made the MAP sensor, and your altitude. Does the MAP sensor read higher than 2.1V when you have your foot in the throttle while driving? Does the 02 sensor show open or closed loop? Better yet if you have TunerPro RT send me your recorded log and I will look at it. I do not visit here much anymore unless I hear of a post like this. I am at http://www.tgpforums.com have a look. 8) I think you better re-read what I wrote because I think you missed something. With key on/engine off you should be reading atmospheric pressure, which is the same as the vaccum to boost threshold when the engine is running. I did assume that his reading was key on/engine off, but I though I made it clear in my post that his reading of 2.1v was ok under those conditions. Quote Link to comment Share on other sites More sharing options...
Pontiac6KSTEAWD Posted March 17, 2006 Report Share Posted March 17, 2006 i still say its the injectors. I think you should OHM test them befor anything. When I got my TGP, it had been sitting for 6 years, and because of it not running, and whatever, all the sensors read wrong, but all were actually ok. Not sure why this was. But after I got it running half decent, I rechecked all the sensors with my freinds bear machine. And all checked out fine. Then the injectors went, and they tested all screwy again... It was most baffling. Quote Link to comment Share on other sites More sharing options...
tcristea Posted March 17, 2006 Author Report Share Posted March 17, 2006 And the 2.1 was with key ON/engine OFF but the volts didnt go higher that 2.3 with the engone ON. Quote Link to comment Share on other sites More sharing options...
tcristea Posted March 17, 2006 Author Report Share Posted March 17, 2006 i still say its the injectors. I think you should OHM test them befor anything. When I got my TGP, it had been sitting for 6 years, and because of it not running, and whatever, all the sensors read wrong, but all were actually ok. Not sure why this was. But after I got it running half decent, I rechecked all the sensors with my freinds bear machine. And all checked out fine. Then the injectors went, and they tested all screwy again... It was most baffling. I will certainly test them again IF I can get the thing running half decent and see what they say. Quote Link to comment Share on other sites More sharing options...
Jeff M Posted March 17, 2006 Report Share Posted March 17, 2006 Still sounds like there is some hanging only on the thinking of the proper MAP volts, so those first. Volts range from 0-5 volts (1-1.5 to 4-4.5 actually), with lower volts meaning more vacuum, and with half way being no vacuum and no boost, basically atmospheric pressure which can be seen with the engine NOT RUNNING and the key in the “On†Position (where the computer checks for atmospheric pressure), higher volts past 2.1-2.5 being the boosted areas. So if you have around 2.1 with ignition on and engine NOT RUNNING then that is correct and shows no problems there. BTW, higher altitudes would show less pressure/more vacuum with the thinner air so if you see 2.1 to 2.5 at sea level, should see less than that at higher altitudes. With that the next thing is what the frick is Jeff talking about, my manual does not agree with those voltages, well that is stupid GM not telling Helms the differences with this being a 2 bar map that is why I quoted the above. So toss out those book values as it applies to a 1 bar map sensor that would show 3.8-5 volts at sea level with ignition on and engine off, and around 2.1 volts up where the air heads live (don’t shoot me ). If it’s that rich all the time must be fun trying to start it?????? Either cracked crossover has fried your o2 sensor, and/or fuel pressure regulator is bad, easy enough to pull off the vacuum line to the FPR and suck (or blow depending how much you like this car), if it does not hold a vacuum then don’t suck too hard or you will have to swallow, sheeze, who started this , then it’s a bad FPR which will make it run rich all the time outside of the range of the computer being able to help, even with my chip . Like others say here, do the usual like a tune up if not already done and you forgot to tell us , then on to the last few things messing things up. Also the vacuum line to the FPR also goes to the MAP sensor so if there is a leak there, double-whammy rich chances then! Jeff M Quote Link to comment Share on other sites More sharing options...
skalor Posted March 17, 2006 Report Share Posted March 17, 2006 but the volts didnt go higher that 2.3 with the engone ON. Even under boost?? Quote Link to comment Share on other sites More sharing options...
tcristea Posted March 17, 2006 Author Report Share Posted March 17, 2006 I put that in a few replys up which is why you probably didnt see it and because like you said I forgot to mention it up front :shock: I did pull that block of hoses and the ECM did put the car in limp-home mode but the O2 I replaced as well. I'll check the vacuum on that as I didnt do it when I replaced the O2. Quote Link to comment Share on other sites More sharing options...
tcristea Posted March 17, 2006 Author Report Share Posted March 17, 2006 but the volts didnt go higher that 2.3 with the engone ON. Even under boost?? Yep Quote Link to comment Share on other sites More sharing options...
Jeff M Posted March 17, 2006 Report Share Posted March 17, 2006 but the volts didnt go higher that 2.3 with the engone ON. Even under boost?? Yep :shock: Ohh, I did not catch that either :oops: then DO NOT (you might already know this, lots of times I speak to others who might read this later and not know :read: ) test drive boost with a bad MAP, MAP Vacuum Line or whatever, if the ECM does not see boost, you don't get enough fuel even if your car is running rich other times So yea, keep on this till you get the MAP volts to move, I assume they don't go down when the engine is running/has a vacuum? Then for sure there is something still there and once fixed, might just fix you up damn good If the vacuum line is cracked (sounds like that is all that is left) then make sure the EGR Tube is not cracked and leaking hot exhaust into that area or it will happen again :!: I say this as I have heard of it 3 times which is "common" enough for me to just want to make sure! Jeff M Quote Link to comment Share on other sites More sharing options...
TGPilot Posted March 17, 2006 Report Share Posted March 17, 2006 The map voltage actually looks fine to me. It's a two bar map sensor and the lower the voltage the less pressure you are seeing. So with the key on/engine off you will read atmospheric pressure. At ~2.5v you should be at see level and since you are 750 above sea level I would expect the sensor to read a little lower. I expect you probably have the regular TGP ailments...leaky injectors and a bad crossover. Jesus Skalor! I am sorry man! I did read it wrong when I quoted you. Oh well when a person has as many numbers in their head like I do right now with 3 different business dealings going on...I guess it gives room for error! I just hope I do not do that with the companies I am dealing with and just look like an idiot on a car forum! :oops: Again my apologies! :oops: You are ABSOLUTELY CORRECT! My car key on / engine off is 1.82V. I am 6000+ feet of course. Quote Link to comment Share on other sites More sharing options...
Jeff M Posted March 17, 2006 Report Share Posted March 17, 2006 The map voltage actually looks fine to me. It's a two bar map sensor and the lower the voltage the less pressure you are seeing. So with the key on/engine off you will read atmospheric pressure. At ~2.5v you should be at see level and since you are 750 above sea level I would expect the sensor to read a little lower. I expect you probably have the regular TGP ailments...leaky injectors and a bad crossover. Jesus Skalor! I am sorry man! I did read it wrong when I quoted you. Oh well when a person has as many numbers in their head like I do right now with 3 different business dealings going on...I guess it gives room for error! I just hope I do not do that with the companies I am dealing with and just look like an idiot on a car forum! :oops: Again my apologies! :oops: You are ABSOLUTELY CORRECT! My car key on / engine off is 1.82V. I am 6000+ feet of course. No worries mate, just did a better goof myself yesterday (yep, I am bragging ) and told the wife "Shit happens" and that is why they call it "Shit" . And THANKS Kenny, that helps me hear and confirm about your 1.82v at 6,000+ feet 8) , sure shoots the hell out of the service manal Jeff M Quote Link to comment Share on other sites More sharing options...
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