My 84 cavalier will not run right, has no check engine light. I suspected the temp sensor and replaced it. After that I replaced nearly every sensor, the ecm and numerous other parts. I finally got a GM shop manual and checked the voltages at the ecm. They all check out except the temp sensor. I'm getting 5 volts, when I should be getting .7 volts. This confirms what I thought all along, the ecm thinks the engine is very cold, but I can't figure out why. I checked the temp sensor with a ohm meter, even though it is brand new. The connectors look good, I have no resistance in the wires from the sensor to the ecm. I've been using an ohm meter to look for shorts across the wiring all day. I can't find anything wrong. Why am I getting 5 volts from my temp sensor?

Let dig into this on my end.I do not want to think to hard on it tonight and make a wrong suggestion.I will follow up once I do my research and or think on it.

I am still working on some thoughts for your issue.I know your year model but need to know a touch more.I would go with my gut and say it is a 2.0 ohv engine code P?Before you do more harm than good try this 1 thing.Disconnect the vacuum line to the EGR valve and see if any thing improve's.I have a alternate idea already but,I am holding my thoughts on that before you try my first suggestion.The temperature sender is tied into the tps grounding wire to the ecm and I doubt that is the culprit as part of the grounding right now(cough).The ecm runs the engine based on numerous conditions and while the temp sender may be newer there are other factors that contribute to how this sensor with others work to make the car run smooth together.Try my no cost idea and let me know.I have be scrolling thru my technical books to make a better diagnostic recommend.

I read your post in maintenance.Did you unhook the egr valve vacuum line?This can help rule out this part.I forgot you posted there first and had suggested this check prior.Just unhook it as the line unhooked can determine if the egr is staying closed or open and run fine unhooked.

It is 2.0 vin p. I don't think the temp sensor is the problem anymore. Page 6e2-14 in the manual says .7 volts but looking at page 6e2-36 and 37 it looks like the voltages should be higher and the internet seems to agree. When I check the circuit with an ohm meter I get correct resistance. That .7 volts seems like a typo or maybe a minimum voltage. I don't think the egr is the problem. I already tried sealing the ports with a piece of cardboard clamped under the egr and it ran the same. I'll try disconnecting the vacuum line later if I have time. Part of my problem is just finding time to work on it.

I just checked the voltages with the engine running, which I hadn't done before. I'm getting 13.5 volts from the pulsair solenoid. According to the diagram on 6e2-14 it should be 0 volts. I already replaced that because it only had 13 ohms, when it should be over 20. That's also why I replaced the ecm because the manual says it can wreck the ecm if the resistance drops below 20 ohms.

Almost forgot, I also had no signal from the oxygen sensor even after driving it for a bit.

Just read oxygen sensor voltages are very low, I will have to check that again.

On the egr check there the only thing needed to verify if that component is failing is just (UNHOOK) the vacuum line and done.If it improves just replace it.As for the o2 sensor if it is very old I would just replace it.If this component is failing typically a low voltage or signal will make the car run like crap.Being the wiring for the oxygen sensor is so close to the exhaust manifold I would make sure you replace the part,use anti seize on the threads and,heat shrink the connecting point and place conduit over the entire wire for protection.And fyi a failing oxygen sensor will not always set a (cel) as the car will in most cases run poorly.

Disconnected the egr, no change. Also, opened the egr with my fingers, made it sputter worse than it already was. I rechecked the o2 sensor circuit, seems to be working. Already replaced the o2 sensor a couple weeks ago, even though I didn't think that was the problem. Just did it cause I'm running out of ideas. Feels like I'm getting a small amount of steady suction from the pulsair. I already replace the solenoid. I think the valve might be leaking. Putting my finger over it didn't help. Tomorrow, If I have time I think I'll stuff a rag In the pulsair intake and try driving around so the ecm can readjust.

Disconnected the vacuum from the pulsair system, still getting suction. Looks like my secondary air injection valve is bad. Of course nobody has it in stock, waiting for parts again.

New valve, starts better, but it might just be the cold weather. I disconnected the battery, rechecked the timing, and tried driving around. It gets worse, not better as I drive it. So I sat in the driveway with it idling, probing the wires on the ecm with a volt meter. It is running rich (but not enough to trigger a check engine light) until the pulsair opens, and it idles higher and leans out. I disconnected the vacuum line from the canister purge, no change. The manual says to check the HEI shielding. I already checked it with both an ohm meter, and I used the tach function on my multimeter to compare the engine speed at the coil with the reference wire. No problems there. Since I already replace the fuel injector, regulator, idle air control, map sensor, and tested or replaced everything else I can think of, my only idea at this point is a clogged fuel return line. My brother has a fuel pressure gauge, but I don't see anywhere to hook it up. Do I have to cut the line? Buy some fittings? Any thoughts?

I am wiped out tonight.Let me revisit this Friday.Plus I can think on it.

I disconnected the fuel return line and blew it out with an air compressor, took it for a drive. The check engine light came on, now it is running lean and not making vacuum. So I blew out the fuel line, and drove it again, the idle air control closed most of the way so it is making vacuum again, but still very lean. I think it could be the fuel pump, but that kind of doesn't make sense. The (brand new) fuel regulator should be doing the job that the restricted fuel return line was doing before. The parts stores weren't any help with hooking up a fuel pressure gauge, but I think I found some fittings at Fleet Farm that will work. I'll update when I have time to work on it.

This might sound silly but I am going to suggest this.Check your exhaust manifold for ANY cracks in the piping on the top side were the 4 into one pipe are.The 2.0 and even 1.8 engines are notorious for cracking and causing a combustion leak.I would not go as far as removing it but a good (eye) view with good light at the joints are in order.If the exhaust is cracked it can wreak havoc on how the car runs in some respects.If you ever replace the exhaust manifold you (DO NOT) use a gasket just metal to metal.I am sitting here just pondering the issue.Just one question more in regard to the fuel pump.How old is it? Granted the car runs and if the pump was failing the car typically would run briefly and cut off.However if your strainer on the pump as (crud built up) on it can make the car run like crap and or the fuel of today with ethanol in it does not help either.Let me think on this a touch more.I have replaced every sensor on my ride and new fuel pump and sending unit and exhaust components and tbi rebuilt.1 more question how old is your cat convertor and muffler?

Pretty sure there are no cracks in the manifold, but I'll take a look. Muffler is new, cat and fuel pump are original, I think. Car only has 88,000 on it. Bought it 6 years ago from the grandson of an old lady that only drove it to church and the grocery store with only 40,000. I think all the sludge in the fuel settled in the fuel lines from not being driven. Probably has some on the strainer too. My theory at this point is that it was running rich from the clogged return line. And it is lean now because the regulator probably always lets some gas bypass it, so if the fuel pump is not delivering enough volume because it is either clogged or wearing out it can't build enough pressure. And I do have full tank of gas.

I would say even though the fuel pump works I bet hands down the strainer is (toast) and debris is coming into the fuel system.The short on my end is I replaced my fuel pump back in 98 and lasted up until 2014 when the pump went bad and the strainer was (Done) .I would consider dropping the fuel tank and replace the fuel pump and strainer and you might want to consider doing the sending unit at the same time.The problem with todays fuel is the ethanol just corrodes the fuel system and gums up every thing!!!!!! I soley only keep about 2 gallons of fuel in my car as it sits more than I run it and the fuel can go stale.I run 93 octane yes with ethanol 10% but this is far better than the low end 87 grade.I am lacking decent sleep due to some meds and just tired.I will walk thru some ideas later when I am not not super tired and elaborate some more details.

Only 4 psi, yep, need a pump.

Please buy (ONLY) a TRUE AC/DELCO fuel pump!!!!!!!!!!!!!!!!!!!!!! The aftermarket pumps fail like you would not believe.I would also go ahead and replace your sending unit at the same time.Now you will not find a sending unit for a 84 and even my 85 are NLA.However the Good news is buy a sending unit for a 1986.I may link my original post sharing the parts I used on my entire fuel tank restoration after this with cost,parts, and explaining the variables.I will say with the new sending units you do have to add new wire for the plug going to the sending unit lets say female end to meet the male end as it is only like two feet long and not like oem.

http://www.j-body.org/forums/read.php?f=28&i=18957&t=18957 My car running again after the said work(video) is on page2! If you have any questions just ask.I went thru my entire fuel tank restoration with all new hoses clamps,just well all of it.This was march of 2014 on completing.