Pontiac Firebird 94, V6 210K miles: Engine Starts and dies

Chaud

Sr. Member
Joined
Dec 18, 2006
Messages
171
Likes
0
Points
16
#1
After having parked for 2 to 4 hours, the car starts and dies within 10 seconds. After that it does not start even after 5 or 6 tries and then it starts again and dies immediately. Fuel pressure checks out good . It am assuming ignition system is working good because when it starts engine runs smooth. However, I did not perform any checks on the ignition when engine does not start. I would definitely check that out but is there anything else like sensor or relay I need to check too. Appreciate your help.
 
Joined
Nov 14, 2006
Messages
4,919
Likes
53
Points
48
Age
119
#3
as nick2 said ck maf- sometimes just unplugung may help troubleshoot.
any ck eng light?
security light?
what is fuel pressure- we need psi?
 

Chaud

Sr. Member
Joined
Dec 18, 2006
Messages
171
Likes
0
Points
16
#4
Thanks guys for your support. This car does not seem to have MAF sensor. Only I could discover was MAP sensor (Manifold air presure), IAC , and air temp etc. If it does have , pls adv location. On the other questions..
- "No" ck engine light on the dash
- Fuel pressure 41
- Security light has been on for the last 5 years but car started and ran fine.
**Additional information** As soon as the car starts, it quits with a backfire. Do you think it could be timing chain-slipped, moved from the TDC etc. Is there a test to check timing chain if it is a problem or not? But the puzzle is that when car starts it runs good.
Thanks
 

billr

wrench
Staff member
Joined
Mar 12, 2007
Messages
6,521
Likes
83
Points
48
#5
In your original post you say "After having parked for 2 to 4 hours, the car starts and... Clarify, does it ever start and run OK, like only when cold, or only when hot? Do you have a reliable and patient helper who can do the start-and-die routine while you check for ignition timing, manifold vacuum, fuel pressure, etc. while it is going through the start/die cycle? The Inlet Air Temp (IAT) and Engine Coolant Temp (ECT) sensors are both pretty easy to test and can greatly affect startability, do you know how to test those sensors? The MAP sensor can also be tested, but it's a little bit more complicated. Let us know what your skill level is, especially with an electrical multi-meter.
 

Chaud

Sr. Member
Joined
Dec 18, 2006
Messages
171
Likes
0
Points
16
#6
The first time I started the car after having parked 4 days, the car started as normal and ran for about 10-15 seconds and died abruptly with a gasp as it is at the verge of backfire. I tried multiple times again and it started once and died immediately. By this time battery was juiced out and I have to re- charge. Next day, I tried again with a fully charged battery but no luck. Tried again today and It barely started but not to the point of idling and died with a big sound of misfire. All this time engine has been cold. The fuel pressure reading I took was without engine running rather fuel pump was turned on with ignition key. I could hear the pump. The reading on the gauge was 41. My knowledge and understanding of electronics circuits and testing is above average and rate myself as A-. Also I would rate myself Level B for mechanical work on the car. Yes, I do have extra help to assist me in doing this job. I hope this background will help you to guide me where and what to do next to isolate the problem. Appreciate your help very much.
 
Joined
Nov 14, 2006
Messages
4,919
Likes
53
Points
48
Age
119
#7
IMPORTANT
when you first turn key to run/start does the CK eng light come on @ 3seconds then go out?

you have a fuel pressur gauge,watch that reading as you try to start....steady or droping also test the pressure and watch for any evidence of leak down after cranking, dbl check that psi as 41 is low border line,
right next to the attaching point for gauge is the FPR - take a look at the vac line tthere should be NO evidence of fuel in vac line.
 

billr

wrench
Staff member
Joined
Mar 12, 2007
Messages
6,521
Likes
83
Points
48
#8
My guess is the fuel/air mixture is way off, either too rich or too lean. Here is what I suggest:

Disable the Fuel Pump (FP), easiest way is to remove the FP relay. Then remove all the spark-plugs so as to inspect them, inspect the wires, and take compression readings. While this is going on any remaining fuel pressure or puddling in the intake should dissipate. Plug wires can be checked with an ohmmeter, stock ones should be about 10K ohms/foot of length. Clean and gap the plugs, if needed, then re-install plugs and wires. Now try to start, with FP still disabled, spraying carb-cleaner into the Throttle Body (TB) intake. If it will start, and maybe even keep running longer than the 10-15 seconds as you spray carb-cleaner in, then it is further proof the ignition is OK and it really is a fuel problem. If so, then pull off the electric connector to both the IAT and ECT sensors and inspect both the sensor pins and harness sockets for corrosion, especially the ECT sensor and connectors. Also look there for any signs of wetness. Those should both be two-wire sensors. If you find a one-wire "ECT" sensor, then that is feeding the dash gauge is the wrong one sensor. One wire on each of those sensor harness connectors goes to chassis ground. Check that with your ohmmeter. The other wire on each harness connector goes through a pull-up resistor in the ECM to +5V; so if you turn the ignition "on" you should read 5V at those sockets with the harness disconnected from the sensors. Although the IAT and ECT sensors are different, one lives in liquid, they are both thermistors with the same electrical characteristics. They range from 100K ohms at -40F to 177 ohms at 212F. Assuming your cold engine is about 70F, the reading between the two sensor pins should be about 3K ohms. That should keep you amused for a while...

I just saw the post by kev2, check out that FPR first, that's also real easy to do!
 

Gus

wrench
Joined
Dec 8, 2006
Messages
2,421
Likes
0
Points
36
#9
OK, has the vehicle been scanned for codes?

As the guys have asked, what is fuel pressure during cranking and when it dies? Does the pressure hold?...definitely check the vac line to the fuel pressure regulator....

Have you checked for spark, on all 6 cylinders?

I assume this is a 3.1L?

When the vehicle won't start, open the throttle plate, and spray some carb cleaner in there.....wait a few seconds......now have some one crank the engine and spray carb cleaner into the throttle body(plate closed)......if the vehicle starts and runs, and fuel pressure is ok, your injectors may not be firing......not sure if this is multiport(won't have a cam sensor), or sequential(will have a cam sensor).....

Hear is where it gets tricky.....if it is an injector problem, and it's multiport, 3 injectors are driven by one driver, so if there is a problem with one injector(injector itself, or wiring to it), it can take out all three injectors on the circuit......if this is sequential(has a cam sensor), one injector circuit that is bad, only takes out one injector.....

If this is a 3.1, the injectors are all under the upper plenum,,,,,,,,the only way to check it, is disconnect the harness and read resistance....since the injectors in multiport are in parallel, they should ohm out for 4 ohms on 1-3-5 circuit, and 4 ohms for 2-4-6 circuit.....on sequential, each injector ohms out at 12 ohms.....

One reason why I think it might be injectors or the wiring, is, if you have spark, and it runs with carb cleaner, I have seen mice get under there and eat the insulation to the injectors, shorting them out......

Now the other possibility, is that security light....you say it's been on for awhile.....if that is the poblem, it won't send a fuel enable signal to the ECM......
 

Chaud

Sr. Member
Joined
Dec 18, 2006
Messages
171
Likes
0
Points
16
#10
Thank you Kev,Bill and Gus. I am overwhelmed with support and ideas. I will follow through all these suggestions and report as soon as each idea is tested. Thanks again.
 

Chaud

Sr. Member
Joined
Dec 18, 2006
Messages
171
Likes
0
Points
16
#11
No codes were read. Now I can't read anymore because I put a new battery in because the other was loosing power quickly after couple of cranks.
No change of fuel pressure 41 while cranking. So fuel system seems to be working. Next after multiple cranking, engine did not fire at all. So I decided to check if plugs are being fired are not. To my surprise I found no spark voltage coming out of any plug wires. So whatever was firing before is totally dead now. I started thinking what component it can be? I thought of crankcase position sensor. But to get to it I have to take out the crankcase pulley which is somewhat complex. So I decided before I dive into it, I should check out the coil pack input voltages. I have the feel it is CPS but not sure. Any thoughts because now the starting situation is not the same as I described earlier.
Thanks
 
Joined
Nov 14, 2006
Messages
4,919
Likes
53
Points
48
Age
119
#12
IMPORTANT try to answer the questions that were posted
when you first turn key to run/start does the CK eng light come on @ 3seconds then go out?
GUS asked is this a 3.1L?

then we can give the troubleshooting for correct eng- ie CPS test, inj pulsing, coil test.... etc

PS you indicated you have a DVOM and are comfortable using it -correct
 

Chaud

Sr. Member
Joined
Dec 18, 2006
Messages
171
Likes
0
Points
16
#13
ck engine light does come on and stays on even after 10-15 seconds. This car is 94 model so it does not have OBDII plug rather a similar plug with 4 to 5 pins in it. Can we read code without buying a fancy code reader? I look forward to your suggestions.
I do have a DVM and can use it very effectively.
Thanks
 
Joined
Nov 14, 2006
Messages
1,395
Likes
1
Points
38
Age
119
#14
I had a coworker who owned a firebird around the same year. He was having a similar problem, he figured it out after he swaped parts from a parts car. In his case it turned out to be bad fuel injectors. My source says the resistance should be 11.8-12.6 ohms at 140 F. Since you have a DMM and know how to use it, I would look in to it.

Ford_Dude
 
Joined
Nov 14, 2006
Messages
4,919
Likes
53
Points
48
Age
119
#15
sounds like you have what is often called OBD1.5 - and yes a scanner specific to it s needed*
ok lets start simple easy
still not clear if this is the 3.1L ?


check under hood fuses #9 and #10 inj fuses both 7.5amp. hot n run/start
also under hood fuse #11 a 10 amp, ign powers the coils CKP CMP....

you said no spark, unlikely all 3 coils are bad - did you ck more than one coil for spark, maybe try a plug from each coil, removing a coil will expose plug pins, probe with ign on, one should have 12v yes no?

not sure which eng- are the injectors accessable we would want to probe pink wire 12v in run yes no.

* OBD diagram - that it?
http://www.troublecodes.net/GM/