94 Bravada wont start now

My gf's Bravada recently had the fuel pump go out and it required the pump and sender unit to be replaced. Before the pump went the truck started fine no problem, now it turns over but just wont start. Ive checked fuses, distibutor ignition, the only thing i have found is a spark that is not 100% but not bad. Any Help or idea's would be much appreciated.

did it ever work after putting the new pump in? check the fuel pressure at the engine. there's a shraeder valve (like a tire valve stem) on the left rear of the engine. you can use a tire guage to check it. did you change the fuel filter at the same time as the pump?

It has not started since changing the pump but, it is getting fuel we have checked. We even tryed squirting fuel directly into the intake and still it did not start. Could it be the ECU? Also we have not changed the fuel filter. This is really racking our brains.

fuel + spark means fire. unusual for an ECM to totaly fail. you can try to read any ECM codes by jumpering the connector under the dash right about where your right knee would be when driving. jumper the two pins in the upper right hand side with a small piece of wire or a paper clip (see pic below) then turn the ign switch to the run position to display the codes

http://s-series.org/albums/album81/OBDI_OBDII_PIN_WIRING_WEB.sized.jpg

you might also check the crank position sensor connector to see if that's the problem

Check the fuel pressure...gotta be around 60 psi.

Okay, rechecked and fuel pressure it is good. I believe it is flashing a code 12, which is faulty ECU. I also believe that fuel is stopping somwhere between the pressure gauge and the injectors. The plugs were pulled and were dry. So I'm still thinking ECU. Any other idea's?

Okay, rechecked and fuel pressure it is good. I believe it is flashing a code 12, which is faulty ECU. I also believe that fuel is stopping somwhere between the pressure gauge and the injectors. The plugs were pulled and were dry. So I'm still thinking ECU. Any other idea's?


code 12 is start of file and end of file. the ecm will flash code 12 three times at the start then flash any codes stored three times each and then flash code 12 three times again after the last code. sounds like the ecm is fine if it's responding.

this post has some good pics of the fuel lines and spider after the pressure test point: http://www.automotiveforums.com/vbulletin/showthread.php?t=518850

After turning the motor over a few times, smell the exhaust tailpipe for a gasoline odor. No odor-no fuel. If you have a strong gasoline odor, likely not enough spark. The ignition coil does get weak after this many years.
Can you hear the fuel pump come on when you turn the keyswitch on?
Exactly how much fuel pressure did you read on the pressure gauge?

There is a code 12, which is faulty ECU. Fuel pressure is at manual spec. We did try a new ignition coil and no change in spark so I think it is ok. We can hear the pump come on and there is no unburnt or burnt gas smell from exhaust.

There is a code 12, which is faulty ECU. Fuel pressure is at manual spec. We did try a new ignition coil and no change in spark so I think it is ok. We can hear the pump come on and there is no unburnt or burnt gas smell from exhaust.


read how to do it here: http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/18/ba/bd/0900823d8018babd.jsp

notice step 5 clearly states that code 12 is not a fault code

did you check the crank position sensor? that's a common cause. the fuel injection will not function without a signal from the crank sensor. . here's how to check it. http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/18/b8/a6/0900823d8018b8a6.jsp

What's the fuel pressure and how did you check it??

Bad news fellas...the 1994 Bravada is OBDII.
The good news is an OBDII scanner will likely point to the exact problem.
More bad news...the '94 OBDII was not quite complete and will likely require a repair shop/dealer type scanner like the $$$$ Snap-On unit.

From our 'ol buddy Blazee:
http://www.automotiveforums.com/vbulletin/showthread.php?t=553044
Thanks again Blazee!!!

Bad news fellas...the 1994 Bravada is OBDII.
The good news is an OBDII scanner will likely point to the exact problem.
More bad news...the '94 OBDII was not quite complete and will likely require a repair shop/dealer type scanner like the $$$$ Snap-On unit.

the 94 might be an OBDII, dpending on vin number. Shucks, Kragens, and Checkers auto parts stores loan/rent the scanner you need for the OBDII since you can't take it there if it won't start.

looks like the ecm and trouble codes vary by vin number as do a lot of parts on the 4.3, as i found out the hard way. found this cool site: http://www.troublecodes.net/GM/

or go to this link for most makes: http://www.troublecodes.net/technical/

Well the vin is definitely OBDI. I didn't personally check the fuel pressure but, my gf father checked it against the manual and said it was correct. We havent checked the CPS but we can. The reason I say I am thinking ECU is the Hayes manual says for the model of Bravada I have there is a code 12.:banghead: I'm ready to throw caution to the wind and try the computer route.

Well the vin is definitely OBDI. I didn't personally check the fuel pressure but, my gf father checked it against the manual and said it was correct. We havent checked the CPS but we can. The reason I say I am thinking ECU is the Hayes manual says for the model of Bravada I have there is a code 12.:banghead: I'm ready to throw caution to the wind and try the computer route.

that's a shotgun approach, stop throwing parts at it. as Chris once said to me "do yer daignostics". this is from the repair manual: Code 12 is not a fault code. It is used as a system acknowledgment or handshake code; its presence indicates that the VCM can communicate as requested. Code 12 is used to begin every diagnostic sequence.

the above info remains the same for both the OBDI and OBDII. if it's an ECU (or ECM, VCM, PCM or what ever you want to call it) problem, i'd be surprised. but go ahead and try a new one. you'll have to get an exact match from the recyclers, otherwise it's a dealer only part. a used / reconditioned one will cost you over $300. maybe you can find someone with the same vehicle that will let you borrow one. or you can take your's out (easy to get to) and trot down to the dealer with it. get it read, cleared, tested and reprogrammed with the latest eprom update on their test bed. let us know how it turns out.

If the truck had Throttle Body Fuel Injection (TBI), the fuel pressure spec is 7.5 to 9 psi....not enough for the Central Point Fuel Injection on ya'lls Bravada which specs 55 to 60 psi. I can't see a motor starting and running then after changing the fuel pump frying the computer unless ya'll had to arc weld the fuel tank back on.

Thanks for the 3.1 motor info Eric.

does the 94 bravada have the pass-key security pellet in the ignition key?

does the 94 bravada have the pass-key security pellet in the ignition key?

I don't know.

well chris, how about your 97?

i think the origional pass-key system system shuts off only the fuel pump if it doesn't see the key pellet and you can crank the engine all you want with no start. the pass-key2 system shuts down both the starter and fuel pump too. the way to tell if you have a problem with the pass-key system is to turn the key to the run position. if the security light flashes you won't be able to start the vehicle, if you get a solid light on you're ok.

i found this out the hard way on my pontiac when i had a no start situation this weekend and did some research. the dealer wanted over $500 + towing to fix it and the local lock shop quoted me $200 to change the ignition switch, but maxwedge posted a bypass that cost less than a dollar in parts and took less than 15 mins in the parking lot to get me going again. thread is here: http://www.automotiveforums.com/vbulletin/showthread.php?t=546556

thank you maxwedge and all the other posters that help out here, you've saved me a bundle of cash.

No, it doesn't have one either but the young'uns '91 Camaro does and it's been a pain in the past. I read there's a fix for it but then there's no antitheft.

No, it doesn't have one either but the young'uns '91 Camaro does and it's been a pain in the past. I read there's a fix for it but then there's no antitheft.

yes, that's true, but do the thiefs know there's no anti-theft system still active? sometimes the appeareance of, or knowledge of a theft control system is enough to make them to move on.

anyways, i bought the pontiac for only $1,500. the bypass works for me.

What do you think of a hidden switch in that circuit with the trick resistors?

What do you think of a hidden switch in that circuit with the trick resistors?

thats a great idea. tossing a toggle switch into the circuit would be cheap and easy, or you could even put a key operated switch in. mine kinda is switched since i cut the wires on the ignition side of the connector and soldered it to the leads so that i can unplug it and take it with me or lock it in the glove box when i leave it at the airport.

wonder if i can run a wire over to the stereo and rig a switch to disable it when i remove the stero control panel. kill two birds with one pull, and even the load levler knows how to put the stereo panel back on.

If the antitheft needs to see 12 volts, the electric antenna circuit, if so equipted, could power it.