hi I have a 1991 camaro RS with a TBI 305. I have put in a new ECM, TPS, MAP sensor, edlebrock air filter, distributor cap, ESC, new ignition coil,upper radiator hose,thermostat and housing,battery, radio and 2 new 6x9" jensen speakers. the thing that makes me madd is that it wont stay runningg! it doesnt pull any codes. But, if I unplugg the TPS and MAp sensor it will start and runn, and when it runs it runs good. Anyone have any ideas??? im thinkin it may be a prob with the fuel delivery, maybe the fuel filter is garbage. THANKS!

 

first take a voltmeter and check the voltage drop from the ecm case to ground. with the engnie running, put positive lead on ecm case and ground lead to a known good ground. preferably straight back to battery.Any more than .1v is considered bad, and needs to be reapired. Then check for 5 volt reference to tps and map both are three wire sensor, one of the wires in each plug should be 5 volts with key on engine off, and key on engine running. lets start here

 

okay i did all that and its good, wat next???

 

It's the Jensen speakers - the ohms aren't right for a 3rd gen, and it screws with the ECM signalling - you have to get Audiovox speakers, or get the ohm converter from eBay.


JUST KIDDING!!!! I couldn't resist!

Is the fuel pump running after start-up? Fuel pump gets current from ECM through relay for priming only, after startup fuel pump gets power directly from battery through the oil pressure sending unit (OPSU) - you may have a bad OPSU, causing the pump to prime only from the ECM, but not continue to run from the OPSU.

 

if you plug either the tps or the map sensor in individually does it stay running?
how does it start when it starts, quickly,right away or do you crank 10 12 seconds before it starts? how long will it run with both unplugged? sorry i didn't respond yesterday, my computer had the power supply take a crap. its beginning to sound like shorted harness but lets not jump right to that yet.

 

it starts readily(@ 1-2sec)With tps and map unplugged, with either or both plugged in will start with more cranking ,but will die within 1-2 seconds. When they are unplugged the car will start and idle ( you can rev up slowly to 3000rpm) for a long time and will not stall.the motor runs very smooth ,When running if i plug in the map sensor it will stumble and die after a few seconds , but the tps kills it immediately .there appears to be plenty of fuel spraying out of the injectors the spark seems strong.

 

You are in the limp mode when both TPS and MAP are disconnected. Do the following test with engine shut off, ignition in run position, all accessories are off.

Check ground wiring connection, and since two sensors share the +5 volt connection - it is especially critical on TPS! With a missing ground ECM will see very high voltage which corresponds to WOT position while engine at idle (if ground is missing)

On TPS connector Pin B (black or gray wire) should be connected to ground lug. Back-probe with a DVM Pin B of the TPS connector and measure voltage - it should be 0 Vdc. If it reads close to 5Vdc ground connection is missing. Pin A of the TPS connector should read +5Volts and Pin C should be 0.5 to 0.6 Vdc at idle and about 4.8 Vdc at WOT.

On a MAP sensor Pin A (PPL) should be ground, Pin C (light green) is a MAP sensor output, and Pin C (Gray) is a 5Vdc reference. With engine off MAP output should be very high around 4.8 Vdc
Check these first.

//RF

 

We checked leads from neg on both tps and map --getting 5 volts to them and with ohm meter there is ground through groung wire lead. we replaced complete distributor . Same issue no better . we also did pressure test and block test --passed both.again car runs great with tps and map sensor unplugged . plug them in and it dies. To be sure about ground should i run a seperate ground wire o ecm from battery? if yes is there anywhere else i should connect to ?(dist,esc,etc)

 

There is no separate ground wire from battery to ECM.

Perform the the following check exactly as outlined below, engine not running but ignition key in run position, both MAP and TPS plugged in.

1) Set DVM to read DC voltage. Note that voltages should be measured with respect to a known electrical ground. On TPS connector Pin A (black wire) measure voltage - it should be 0 Vdc.
2) On TPS Pin C (gray wire) of the TPS connector should read +5Volts
3) On TPS Pin B (Dark-blue wire) should read 0.5 to 0.6 Vdc at idle and about 4.8 Vdc at WOT. When moving throttle from idle to WOT position voltage should increase smoothly. Also depending on TPS type pin assignment maybe different from the one I have listed. What we are looking for is a voltage change! Note the color of wires and their relation connector pins.
4) On MAP sensor Pin A (PPL wire) should be 0 volt
5) On MAP sensor Pin B (light-green wire) should be about 4.5 volts
6) On MAP sensor Pin C (Gray wire) is a 5Vdc reference 5.0 volts.

If you are not seeing above voltages - repeat above, but disconnect MAP sensor first and re-measure all six voltages, and then reconnect MAP and disconnect TPS and repeat. You should have a six row by three column table of measured voltages. If you can not do above - sorry pal - I can not help you. Post your table.

//RF

 

key on tps /map pluggedin---tps in/map out-----tpsout/mapin
tpsa(black) 0 voltsdc 0 o
tpsc(gray) 5 v 5v 5v
tpsb(blue) .4v@idle 1.8v@wot .4v@idle 1.8@wot .4v

map a(ppl) 0v 0 0v
mapb(green) 1v 0v 1v
mapc(gray) 5v 5v 5v

looks like i have a problem not getting enough current from tps forwot(tps is new). also appears as though map sensor current is much to low. map sensor is not new but had switched out with supposed working unit , ansd there was no improvement. What do you think I should go after now? Thanks alot!!

 

forgot to mention when car is running and you plug in tps or mapsensor as soon as contact is made the fuel flow from injectors instantly stops causing car to stumble and die.what ever signal they are sending to ecm is telling it to stop injector pulse. we replaced the ecm , could the prom be bad? Thanks

 

Hey bigD

Just returned from a short biz trip - thanks for the table. From your measurements I see potentially two problems provided that voltage readings were taken as I have outlined in my earlier post.

1) MAP sensor - with engine stopped & ignition on - MAP sensor should be reporting very high voltage values which correspond to low vacuum readings. We are not seeing this and instead you see 1.0 Vdc vs. expected 4.5 Vdc! To verify that a MAP sensor is good or bad you'll need hand vacuum pump (Mityvac or equivalent) to simulate engine vacuum applied to directly to MAP sensor vacuum port. Your sensor should report about 1.2 Vdc when it sees about 18 in-Hg applied at its input and about 4.5Vdc when vacuum is very low - i.e. engine stopped. Again, above is based on the assumption that voltage readings were taken correctly.

2) TPS sensor - this is also somewhat strange, but could be attributed to bad TPS sensor. To check TPS you need to - ignition off, disconnect harness from it and use your DVM to measure resistance between terminals. First insert test leads between Pin A and C and you should see about 4000 Ohms (4 kOhms). If you see much higher values - TPS in most likelihood is shot, but make sure that you make a good electrical contact. If you move throttle you should see no change this reading. The next measurement is a critical one - measure resistance between Pin A to B and then repeat for Pin C to B. Depending on pin assignments you should see 880 Ohm to 4880 Ohms as throttle is moved from idle to WOT. Note A to B should mirror B to C measurements for the same throttle position, but in reverse. See example table below:
Pin----|| Idle || WOT
A to B || 880 || 4880
B to C ||4,880|| 880

Let me know what you measure. I do not believe that your ECM is bad, lets make sure that sensors are not reporting garbage readings to it! If ECM sees strange TPS or MAP readings it will try to adjust fuel delivery based on the stored look-up tables which may make engine operation impossible given actual operating requirements.

//RF

 

I have the map sensor out of car . Checking with ohm meter. pin a to b reads480 ohms---ato c reads lower @390 ohms---bto c reads about750 ohms0 should these read like this ? or is this unit bad? I dont have a mityvac thanks

 

You can NOT check MAP sensor by measuring its output resistance - it's an active sensor that requires supply voltage (5Vdc) to operate. To check MAP sensor it must have DC supply connected along with vacuum source. For all practical purposes your measurements are fruitless. MAP sensors are commonly constructed with a silicon diaphragm which is exposed to engine vacuum to form a strain gauge. Wheatstone bridge consisting of resistors connected silicon diaphragm are buffered by a differential amplifier which outputs a voltage in proportion to inlet vacuum. MAP sensors typically fail due to moisture exposure to silicon diaphragm. However, you can check TPS by measuring its resistance. TPS is nothing more than a glorified variable resistor - DVM in resistance measurement mode can check that. //RF
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You can NOT check MAP sensor by measuring its output resistance - it's an active sensor that requires supply voltage (5Vdc) to operate. To check MAP sensor it must have DC supply connected along with vacuum source. For all practical purposes your measurements are fruitless. MAP sensors are commonly constructed with a silicon diaphragm which is exposed to engine vacuum to form a strain gauge. Wheatstone bridge consisting of resistors connected silicon diaphragm is buffered by a differential amplifier which outputs a voltage in proportion to inlet vacuum. MAP sensors typically fail due to moisture exposure to silicon diaphragm.

However, you can check TPS by measuring its resistance. TPS is nothing more than a glorified variable resistor - DVM in resistance measurement mode can check that.

//RF

 

Thank you for the explanation ---every part you can understand helps in the long analysis. This car was not run for @15months maybe moisture got into it. I am going to try to pick up another one. Thanks again

 

updateon 91 camaro rs--replaced distributor and tried another map sensor and iac valve--same thing still happens. also found a local guy with another 91 camaro rs 5 speed not an auotmatic like ours but having the exact same problem. his car keeps stalling after @5 seconds . I unplugged his map and tps and it will run fine.Some body on line contacted with same problem with their camaro. has anybody experienced this before? could it be the tcc--Iheard this solenoid could cook and that it what will blow out your ecm( which I already replaced) .what does the tcc tell the ecm, does it think my car is in 3rd gear at 4000rpm so when i plug in the map and the tps at idle does it get all crazy? also should i replace the prom chip in the ecm,we retained the original in the new ecm, do they fail? could that be our problem? thanks alot

 

Sounds like there are a multitude of problems.

1) TCC - torque lock up converter is nothing but a glorified solenoid which ECM controls once it detects that vehicle speed is above a threshold. For troubleshooting purposes you can temporarily unplug four pin connector going into your 700R4. It is very rare, but TC can fail due to age and abuse.

2) When you unplug MAP sensor ECM should revert to a limp mode. What makes it difficult on this end is that you do not finish checking voltage levels as outlined in previous post. Swapping sensors blindly will not result in an immediate fix. So, be a good lad and check them MAP voltages and post them here.

//RF

 

did you check the MAP sensor vacuum line. When I installed my Edelbrock TBI intake the vacuum line melted on the intake and made the car run similar to yours. It ran perfectly fine when I disconnected the MAP, limp mode. It is probably something you have already checked but maybe not.♦

 

we did replace the vacuum line to the map sensor--- it is new. we did pull the 4 pin connector off the transmission. the entire pin /contact assemblies are green and corroded thru. two pins just fell off! looks like i will need to get a new connector from a junkyard, and replace whatever part goes into the trans mission. out of all the parts we have played with on this car this is the only part that has not appeared in good condition. it is really corroded bad . Water and road slt must splash up in there . we have not tried to run the car yet to see if this solves the issue but we are hopeful we are onto something.

 

? does the 91 have a Mass air flow sensor or just the iat on the breather pan. I had some simliar probs with a little newer car and it turned out to be the maf instead of the map and tps...

 

this car does not have an maf sensor.

 

Just pulled out fuel pump and little connector hose is all rotted . it would pump some gas but would not buil any pressure. will fix .thanks to all who helped.

 

hooray! with new fuel pump and connector hose , car now runs great with all components plugged in as they should be. Thanks again.

 

this is the this is the sub box im building for the well in the hatch area, im gona cover it with the same material that i redid my headliner with, ill post pics



1991 camaro rs with 1989 firebird TA front end and hood, best of both worlds =)




i did some repainting of the stock valve covers (black) and other plastics in th engine bay anew upper radiator hose and new edlebrock air filter

 

man, i never heard about something like that! that's a real F-rankenstein-body looks nice, glad to hear you got it running again.

 

unfortunately thats why i dont like computer controlled cars cause i know nothing about them. but your ride looks sick. i love that car. glad its finally running. and glad im moving on to carburator lol.

 

thanks guys, im so happy i got it running and i cant wait till i can leagally drive it myself. i only have my permitt lol so a liscence would be great. its my first car and the TBI setup seems okay, i wanted to switch to a carburator but it would cause so many moree problems cus everythings already electronically controlled, my uncle did it and he blew so many tourge convertors. but the hav a kit to manually luck up theconvertor. i just wanted it to run lol

any ideas let me know

 

i reckon that gas prices have decreased a lot lately, but i think that's a lazy excuse for swapping a carb in place of a FI. TBI is really capable and actually easy to tune. there's a hell of a lot more to gain out of FI compared to a stupid old carb, that's performance, driveability as well as economy wise.

sorry for bashing on carbs, but they are outdated. if you want to learn something useful, try FI. you'll quickly recognize that your investment becomes worthwhile.

 

yeah, mine came with the 305 TBI stock, so im just keeping it

 

hey does anyone have any more ways i could clean up my engine or make anything else cleaner? im kinda goin with like black and chrome,but i definitely need to clean my intake manifold