[83t/a kid]

I have an 83 T/A with crossfire 305.I need some help with a diagnosis of the computer inputs.How much does the E.C.T. (engine coolant temp sensor) affect engine performance,and where can I find specs on resistance? Does the TPS (throttle position sensor(s) ) effect the performance,and if so in what ways? Resistance range ? I ask because I have an intermittent running prob with no check engine light,although it will come on if I disconnect things like the MAP sensor. I do not have a scan tool to plug in and I don't"flash" any codes when I jump the ALDL........Suggestions? It sometimes has a HUGE bog,like way loose Q-jet secondary air valve.Rarely happens :no Check engine light when it does. Any help greatly appreciated!!

[LPete]

You'll probably never catch either sensor acting up with an ohm meter. The coolant temp. sensor is pretty much out of the picture after the engine gets to 120 or 130 degrees. If you put a voltmeter on the signal wire (yellow??) it should read somewhere around a volt with the engine hot. The TPS should read roughly .7 V with the throttle closed to a little over 4 V with the throttle wide open. Neither of these would usually cause a problem like you're having, but it's not impossible.

I'd want to verify fuel pressure when the problem happens. The MAP sensor is the main input for engine load -- don't know if it's possible for the hose or vacuum source to get plugged on this engine, but it can on some. These older GMs won't set codes unless a sensor reading is so far out of range that the reading is impossible (shorted or open circuit). They couldn't detect a reading that was within range, but wrong. There are also ignition problems that can act this way, like a coil with insufficient output. I think you'll have trouble solving this without a scan tool.

[83t/a kid]

Ok, thanks.I wanted to verify my own thoughts about it without preconceiving someone elses opinion. If the voltage or resistance to/in the fuel pump circuit were to change for some reason the pump pressure could have this effect on driveability. Maybe a bad wire,contact,or the pump itself could be the culprit. As soon as I can I'll get a gauge on it.What is the pressure spec,do you know ? Anyways thanks,if there is something I might be overlooking please set me straight.Again thanks for your help!! John.

[LPete]

Fuel pressure has a huge effect on driveability. The amount of fuel the injectors squirt is directly related to fuel pressure, and the computer bases its fuel calculation on the expected injection amount. I'll check tomorrow, but as far as I know all GM TBI systems used 9 to 13 PSI (this is TBI, right? -- haven't worked on many). You need to check whatever you're checking when the problem is occuring. Fuel pressure and voltage tests are pretty much meaningless unless tested while it's acting up.

[83t/a kid]

Thanks for the help,L.Pete. Found low fuel pressure during intermittent rough running.Traced this to bad power wire to fuel pump,crimped and mostly broken due to someones careless repair at some point.Fixed wire properly and have not had recurrence.Also did thorough engine check out;compression,timing slop,etc....etc.....found a few cam lobes worn severely and a few degrees of slop in the chain.Compression slightly low,probably from the dead cam lobes in those low cyls....Runs pretty good considering.Thanks again for the advice!