I just got a 1991 Formula 5.7, they car may have sat for a couple years. When i start it up cold (after a few tries) it runs very rough but steady. As it warms up when the temp gets to around 170-180 it just dies. The only way to get it to start then is to hold the pedal to the floor, then it will fire up for a second and die. Any ideas?

 

Check your fuel pressure at the rails.

 

and CTS. If it reads -40C time to replace

//RF

 

It may be dying when it goes into closed loop. Try disconnecting the oxygen sensor to see if that is the case. I assume you're not trying to run it on old gas, right?

 

Checked the FP at the rail, it's 40 PSI so that looks okay. I had the car running a couple more times and it seemed like it was getting a little better, wasn't dying or anything, but the last time it ran very rough died after a short time. Since then i haven't been able to get it started, it doesn't even really try to fire up. After cranking it a few times i can smell gas, pulled the #1 plug and it was dark and smelled of gas. The coil has been replaced, gonna have to check on the SES bulb as it doesn't light up so i don't know if any codes are being thrown.

 

Update ... replaced CTS, no start. Took out #1 plug and connected to plug wire and cranked, plenty of spark.

 

Check the timing with the ECM disconnected. Check your plug wires are in decent shape and fit tight on both ends. Check your plugs, make sure they are all threaded in tight.

If you have a timing light, put it on each plug wire and make sure each one is firing - I had a rough run situation a couple weeks ago on my LT1, and I tried that - had no spark at all on #8. Turned out that the #8 plug wire rubbed through on the power steering pulley when it popped out of its loom and was grounding out. Replaced the wire, and has been fine since.

Thats why I suggest checking ALL the wires for spark with a timing light.

 

Thanks AIR, i've got a set of Moroso 8mm wires laying around, i'll throw those on. I can't get it to start right now so i can't check the timing now. I did pick up
an Actron Elite Pro scan tool, it showed no codes in the ECM and i'm just starting to figure out all the other stuff it can tell me.

 

Check to see if the injectors are the original Multec's. Classic symptoms of them shorting out. What you can also do is to check the resistance of the injectors once they are hot (run the engine until it dies). Pull all of the injector connectors and using a DVM measure the resistance of each injector (across the pins). Any that is lower then 12 ohms is shot. Any lower then 16 ohms is on the way out.

If they are the originals I'll bet several are in the 2 - 4 ohm range. When that happens the ECM can't fire them and the engine dies.

RBob.

 

Was able to get some info from the scan tool(Actron Elite Pro), was limited cause she won't run, got what i could with just the key on ... and it was in the 30's for temp went i got these readings.


Codes present NO
3RD Gear SW ON
4TH Gear SW ON
A/F Ratio 0
AC Clutch OFF
AC Enabled NO
AC Head Pres NORM
AC Request OFF
AIR DIVRT SOL DIV
AIR SW SOL CONV
BATTERY(V) 11.7
BLM 128
BLM CELL 0
CCP Duty(%) 0
CCP Solenoid OFF
CLNT STRT(F) 37
COOLANT SW OFF
EGR DUTY(%) 0
ENGINE RPM 0
EXHAUST 02 LEAN
FAN1 REQUSTD NO
FAN2 REQUSTD NO
FUEL PUMP(V) 0.0
IAC POSITION 160
IDLE REQ RPM 3188
INJ PW(ms) 0.0
INTEGRATOR 128
KNOCK RETARD 0
KNOCK SENSOR 0
LOOP STATUS OPEN
MAP(V) 4.73
MAT(F) 38
02S(mV) 453
02S CROSSCNTS 0
OIL TEMP(F) -39
SPARK ADV 0
TCC LOCKUP NO
TCC SOLENOID OFF
THROTTLE(%) 0
TPS SENSOR 0.63
VATS STATUS OK

 

jim86

Based on the scan tool readout:
MAP is OK 4.73Vdc with engine off
MAT 38F - Brrr it is cold where you're
CTS 37F
TPS is OK 0.63VDc at idle
Bat Voltage is OK 11.7
IAC is at 160 - wide open! (Need to reset IAC)
ECM appears to be OK (at least A/D section) Check injectors per RBob post.

//RF

 

Just ran out at lunch real quick and grabbed some starting fluid. Sprayed some in the throttle body cranked it twice for 7-8 seconds, no hint of it firing.

 

Just checked the oil, it's WAAY overfilled. Like just below the 'see operating manual' on the dipstick. Looks like i'll be changing oil tonite, not sure it has anything to do with my problem but it can't be helping.

 

Put the FP gauge back on today to see how fast pressure is lost to try and get an idea if injectors are leaky. After the gauge was on and the key was on it popped to 40 PSI, after turning key off i waited about 15 minutes and it showed 36 PSI. Is that close to normal?