Just recently started having trouble starting when my car is cold.
Have to turn it over for 4-5 seconds, 3 or 4 times before it will start. Once it starts it runs fine, no problem, no codes. The car has always started up almost instantly when cold, so not sure what might have happened. Only thing I have done recently is replace the alternator, and the problem started showing up immediately after that. Is it possible I did something while changing the alternator?? Car is an 88 L98. Any help would be appreciated. Thanks.

Bob

 

The first thing I would check would be to replace the fuel filter if you haven't in a while.
Next, I would check the fuel pressure the fuel pressure. If you don't own a guage yet, pick one up at Autozone, Pep Boys, etc for about 30 dollars or so. There's a valve on the pass side of the fuel rails right below the 2 vacuum ports on the upper plennum.
The pressure should be about 38-42 psi, although some run a little higher than others. Check the pressure with the car off but the key on.
It could possibly be the fuel pump relay going/gone bad. This is also one of those cheap fixes that ends up being the problem a lot of times. When I got my '86, the relay wasn't even plugged in and it fixed the same problem you have.
The relay is located on the firewall in next to the left side (as you're looking at it from the front of the car) of the brake booster. There's 2 relays and I can't recall which one it for the fuel pump, but you can probably search previous posts for it or someone will chime in.
Hope this all helps.

 

BOB--Having been there done that, have you checked the fuel pump and relay? I had the same problem on my 89 L98. Try this-- turn your key to the on position without starting it. You should be able to hear the pump run for a few seconds and quit. If you cant,99% sure you have fuel pump on its way out or gone.I replaced everything I could think of that was ignition related. Finally took it to dealer,they checked pressure and found only 14-16-lbs. Should be,according to them, around 40-45lbs. If this is your problem,I suggest a new strainer and fuel filter also. Gm parts and labor was 315.00.

 

check to make sure the connection to the engine coolent temp. and mat and MAF sensors are firmly clipped on, that to a large extent controls when the engine ECU knows when to richen up the mix when first starting the engine when its cold. also check the cold start injector is correctly hooked up (its located on the drivers side rear side of the tpi (D and H in the picture)

http://www.chevythunder.com/fuel%20i...%20pg%20AA.htm

READ THIS

http://www.chevythunder.com/fuel%20i...g%20pg%20D.htm

BTW carefully check the MAF sensor, if you broke that hair thin wire due to rough handling that can and will also cause the problem, and while your at it, heres how to remove the injectors if you choose too, BUT ITS VERY UNLIKELY youll need to clean them!
http://www.thirdgen.org/newdesign/te...ctorswap.shtml

MOST PROBLEMS ARE ELECTRICAL /SENSOR OR CONNECTORS THAT HAVE BAD CONNECTIONs NOT FUEL RELATED,BUT CHECK THE PRESSURE ON THE SHRADER VALVE ON THE PASS SIDE FUEL RAIL, IT SHOULD BE AT LEAST 37-40PSI minimum

you should be able to hear the fuel pump kick on as the key is turned and watch the fuel pressure kick up to IT SHOULD BE AT LEAST 37-40PSI minimum
the oil pressure sending switch might be a problem if your having extremely low oil pressure at start up as it cuts off the ignition at pressures under 4 psi.
here read this http://www.c4vettes.com/l98.htm
http://www.c4vettes.com/ecm.htm
http://www.c4vettes.com/sensorinformation.htm

heres a second post that might be of some use to you
http://forums.corvetteforum.com/zerothread?id=598601



[Modified by grumpyvette, 7:08 PM 7/6/2003]

 

Checked all the connections, fuel pressure, did'nt remove the maf. All my injectors were removed and reconditioned by rich at cruizin performance a couple of months ago. How about the fuel pump relay, is there a way to check it??

Bob

 

My 89 exhibiited hard corld starting simlar to yours but I got a code 54. Code 54 indicated relay or pump. The relay was the cheapest of the two. A new relay only cost about $11 so I just replaced it. Problem solved. The fuel pump relay on my 89 is on the firewall between the brake booster and the engine.

Bob

 

:iagree: :thumbs:

 

Just to add about the relay, when it was disconnected on my '86, it didn't throw a code, so it's possible to be bad, but not trip the code. As was said, the relay is only about 10 or 11 dollars, so most people check it by replacing with a new one.

Chris

 

:bs
State your source. This is just wrong. The Oil pressure has nothing to do with ignition.

 

Bob,

There are 2 ways to test the relay. As mentioned buy a new one from NAPA (exact OEM match and cheaper than the dealer at about $12) or swap one of the other relays into its place. The C4 uses several relays under the hood and most all of them are the same. Here are 3 relayss by GM part # for the 88-89 Vette:
14089936 RELAY, F/PUMP (1.055) 88-89
14089936 RELAY, MASS AIR FLOW SEN (POWER)
14089936 RELAY, ENG COOL FAN

Right behind the battery are the MAF power and burnoff relays. The engine cooling fan relay is mounted on the radiator shroud near the upper radiator hose. They are the same relay as the fuel pump relay. You should be able to see the relay numbers on the top of the relays.

 

Brother Quayle,

If you have the factory service manual, check the drivability section, Code 54 schematic. There, you should find the 4 psi oil pressure switch wired in parallel with the fuel pump relay.

Typically, the 4 psi switch and pump relay power output are protected by the same fuseable link and fuse.

dlmeyers 90 coupe zf6 3 speed shocks

 

Ray Quayle

L-98 Engine Start Sequence

When you start an L-98 engine Corvette, a series of events take place that causes the engine to run. Knowing the sequence will help you troubleshoot no start conditions.

Fuel Rail Pressurization:

When you first turn the key to the “on” position, the fuel pump will run for 2 seconds pressurizing the fuel rails. There is a Shraeder valve on the passenger side fuel rail near the rear of the engine and if you measure the pressure there after the pump runs, you should see between 40-42 pounds of pressure. The reading will go to 38-40 pounds nominal once the engine is running.

Initial Crank Action:

If you then rotate the key to the start position (assuming the anti-theft system has not disabled the starter), the engine will rotate.

Once the oil pressure has reached 4 PSI, the oil pressure switch will close allowing the fuel pump to run. (Note that you should have a black oil pressure switch/sender. It is mounted behind the distributor on the driver’s side and if it is not black, it is suspect due to a run of bad units that stayed in the GM parts pipeline for some time).

The distributor will send a string of pulses to the ECM (Engine Control Module) in response to the engine being rotated by the starter. These pulses continue as long as the engine turns (both starting and running) and if they are not present, the engine will not run.

ECM Reaction:

If the ECM sees oil pressure greater than 4 PSI and the reference pulses from the distributor, it will energize the injector drivers which will begin pulsing the injectors on for 4 ms (milliseconds) periods. (In the L98, all injectors on one side of the engine fire at the same time followed by all injectors on the other side firing at the same time. On the LT-1, the injectors are fired individually at the appropriate time).

The ECM will also pull in the fuel pump relay in effect paralleling it electrically with the oil pressure switch. (If the fuel pump relay fails, you can still normally get the car to start and run unless you can’t make at least 4 PSI oil pressure. This is a “limp home mode” feature put in place to allow for a fuel pump relay failure).

The ECM also monitors the TPS (Throttle Position Sensor mounted on the throttle body assembly) and wants to see .54 volts at this time. If it sees appreciably more than 0.54 volts, it will assume the engine is flooded and the driver has pressed the accelerator to the floor to clear the flooded condition and restrict the fuel flow as a result. (.54 volts during start and at idle from the TPS is very important to both starting and run performance.)

Assuming the ignition module is good (meaning there is a spark of sufficient intensity to ignite the fuel), the engine will “catch”.

Engine "Catches":

THE ENGINE WILL NOT FIRE OFF AND CONTINUE TO RUN WITH UNDER 4PSI OIL PRESSURE THATS A FACT


[Modified by grumpyvette, 1:53 PM 7/8/2003]

 

grumpyvette,
Nice piece. You've for the most part got it all right. My request was "State your source." with reference to your statement "the oil pressure sending switch might be a problem if your having extremely low oil pressure at start up as it cuts off the ignition at pressures under 4 psi.". I want to know where you came by the fact that the oil pressure switch cuts off the ignition at pressures under 4 psi.

Granted you changed up a bit and now claim that "THE ENGINE WILL NOT FIRE OFF AND CONTINUE TO RUN WITH UNDER 4PSI OIL PRESSURE THATS A FACT". I assume this was to dissuade my challenge for you to hang on to the end of one of my plug wires as I crank her over with my oil pressure switch disconnected. But you still calim "If the ECM sees oil pressure greater than 4 PSI". I still want to know where the ECM gets its oil pressure input and where you found this information.

In the meantime if anyone is willing to get back behind their distributor to disconnect thier oil pressure switch and try to start their car, assuming you have a good fuel pump relay, I'd love to hear your results.

 

OOOOOOOPPPPPPPPs.

I misread part of this thread. A thousand pardons to all.

Can find no reference to oil pressure and primary/ secondary spark control.

Many people believe that if you loose oil pressure, the engine will quit due to some ECM control. With less than 4 psi, the engine does eventually quit, darn thing will simply sieze.

As a system note, GM on many many systems, used the 4 psi switch as the fuel pump's secondary power source. I have never seen a GM schematic with oil pressure relating to ECM spark control or injector pulse. As stated, the RPM reference signal and injector pulse are related and used by the ECM.

As far as the original post, understand the coolant temp connection on the front part of the engine is still intact? If something is temp related, this is where I would start.

dlmeyers 90 coupe zf6 3 speed shocks

 

dlmeyers,
I'm really sorry to you andl all if I've turned this thread into something other than a cold starting question. I've always tried to use this forum to gather as much info as I could and if I find something that goes against that, I try to find out why the info I'd gathered in the past was incorrect and what the source of this new info is. My experience through hands on testing shows, as you stated, that the oil pressure switch is a secondary power source for the fuel pump. If the oil pressure switch is disconnected, as long as your fuel pump relay is good, the engine will still run. You will surely get spark! If this is different on later C4s with other than the 165 ECM or with a CCM, I'd like to know. I really need to invest in a few more Helm's manuals to cover the later years, I guess.

These distributor reference pulses are also noteworthy here because of another thing the ECM does when it is receiving them. As stated by grumpyvette, the ECM will energize the fuel pump relay for @2 seconds when the ignition switch is turned to ON. The reason the fuel pump stops is because 1) there is no oil pressure and 2) the ECM is not receiving reference pulses. If either happens, the fuel pump will start again. Disconnect the oil pressure switch and crank. When the engine starts to turn, the ECM starts receiving reference pulses and energizes the fuel pump relay. Engine starts. Re-connect the oil pressure switch and disconnect the fuel pump relay then crank the engine. It may take longer to start if you engin doesn't jump to life with a bump of the starter (on the 2 second fuel system prime), because the engine will have to build oil pressure running on the starter, but it will eventually build enough oil pressure to close the oil pressure switch and start the fuel pump. But you will still have spark during this time, the closing of the oil pressure switch at @4psi just supplies a current source for the fuel pump since you have no fuel pump relay. As you said, a secondary power source.