Cold start issue on 89- any thoughts?
05-24-2005, 03:55 PM
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Cold start issue on 89- any thoughts?
Hey guys,
I've got an 89 L-98 that doesn't start nicely when cold, has to be cranked for about 15 seconds before it catches. Once it does catch, it often dies, and then starts just fine. Once it's running, there are no probs. A quick shot of starting fluid will cause the car to fire instantly, but it will often die, and then require more cranking.
My guess with the problem is a fuel supply issue. Unfortunately, I don't have a fuel pressure gauge to verify what the fuel pressure is once the key is on. So- here's my questions.
Does the L-98 energize the fuel pump for a short time period during the initial 'key on' sequence? I'm assuming it would just to bring up fuel pressure. Is there a seperate relay for this event, assuming it exists? (that way I could check for a bad relay).
Other obvious things would seem to be a bad FPR (pull vaccum line to check for fuel), flaky fuel pump (recently replaced, and the car seems fine otherwise- I would think a bad pump would cause it to lean out on the top end), or possibly a bad injector that's leaking fuel pressure. If an injector were leaking fuel that fast, I'm assuming the exhaust would smell rich (which it doesn't)- can anyone confirm that?
Also, is the fuel pump circuit tied into oil pressure? That might explain why I have to crank so long as oil pressure builds if the initial fuel pump surge doesn't happen.
Anything I'm missing? Any other thoughts?
Eric
I've got an 89 L-98 that doesn't start nicely when cold, has to be cranked for about 15 seconds before it catches. Once it does catch, it often dies, and then starts just fine. Once it's running, there are no probs. A quick shot of starting fluid will cause the car to fire instantly, but it will often die, and then require more cranking.
My guess with the problem is a fuel supply issue. Unfortunately, I don't have a fuel pressure gauge to verify what the fuel pressure is once the key is on. So- here's my questions.
Does the L-98 energize the fuel pump for a short time period during the initial 'key on' sequence? I'm assuming it would just to bring up fuel pressure. Is there a seperate relay for this event, assuming it exists? (that way I could check for a bad relay).
Other obvious things would seem to be a bad FPR (pull vaccum line to check for fuel), flaky fuel pump (recently replaced, and the car seems fine otherwise- I would think a bad pump would cause it to lean out on the top end), or possibly a bad injector that's leaking fuel pressure. If an injector were leaking fuel that fast, I'm assuming the exhaust would smell rich (which it doesn't)- can anyone confirm that?
Also, is the fuel pump circuit tied into oil pressure? That might explain why I have to crank so long as oil pressure builds if the initial fuel pump surge doesn't happen.
Anything I'm missing? Any other thoughts?
Eric
05-24-2005, 04:44 PM
#2
Le Mans Master
When you first turn the ignition key to "ON" (but don't crank the engine), the fuel pump should turn on and prime the fuel rails. The pump remain on for about five seconds, waiting to receive a distributor reference signal which lets the system know you're cranking the engine.
If it doesn't receive that signal, the pump shuts down.
Cranking the engine will cause the oil pressure to build. Once it reaches about 4 psi, the fuel pump is again energzied and turns on. So there are two ways for the pump energize - Well, actually three if you include installing a jumper wire to the ALDL.
Try this: Turn the key to "ON" but don't crank the engine. Listen for the pump running. If you hear it running, wait until it shuts down automatically, then wait an additional 10 seconds or so (the pump circuit must reset) and do it again. Then crank the engine. It should fire right away.
If you don't hear the pump running when you first turn the key to "ON" it's probably the relay. If the relay's bad it's the oil pressure switch that's turning on the pump and letting the engine fire.
If you have a fuel pressure gauge, you can turn the key to "ON" while watching the gauge. The pressure should immediately show up on the gauge. When the pump shuts down, the gauge reading should hold for a few minutes before it begins to slowly fall. How long it holds varies from engine to engine, but it should not instantly fall to zero.
If the pressure instantly drops to zero when you turn off the key, then there's a leak either in the tank at the fuel pump, one of the fuel lines or at the fuel rails/regulator/injector(s).
Jake
If it doesn't receive that signal, the pump shuts down.
Cranking the engine will cause the oil pressure to build. Once it reaches about 4 psi, the fuel pump is again energzied and turns on. So there are two ways for the pump energize - Well, actually three if you include installing a jumper wire to the ALDL.
Try this: Turn the key to "ON" but don't crank the engine. Listen for the pump running. If you hear it running, wait until it shuts down automatically, then wait an additional 10 seconds or so (the pump circuit must reset) and do it again. Then crank the engine. It should fire right away.
If you don't hear the pump running when you first turn the key to "ON" it's probably the relay. If the relay's bad it's the oil pressure switch that's turning on the pump and letting the engine fire.
If you have a fuel pressure gauge, you can turn the key to "ON" while watching the gauge. The pressure should immediately show up on the gauge. When the pump shuts down, the gauge reading should hold for a few minutes before it begins to slowly fall. How long it holds varies from engine to engine, but it should not instantly fall to zero.
If the pressure instantly drops to zero when you turn off the key, then there's a leak either in the tank at the fuel pump, one of the fuel lines or at the fuel rails/regulator/injector(s).
Jake
05-24-2005, 11:37 PM
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Does it start OK when warm/hot? If so, it may not be a fuel problem but rather a temp. sensor/ECM problem.
Mine was a cold-start problem only. Turned out to be the ECM not converting the temp sensor input to a temp. that would increase the pulse width of the fuel injectors to start and run a cold engine; much like the function of a choke on a carburated engine.
If it is the ECM, then you may be having other problems: main electric fan coming on early/late; engine idle is erratic, doesn't return to 600 rpm when you come to a stop? Basically, whatever the ECM controls will not function as it should.
Since I replaced the ECM, my 89 runs like new. Everything works like it should; even the tranny (auto) shifts like it should.
Mine was a cold-start problem only. Turned out to be the ECM not converting the temp sensor input to a temp. that would increase the pulse width of the fuel injectors to start and run a cold engine; much like the function of a choke on a carburated engine.
If it is the ECM, then you may be having other problems: main electric fan coming on early/late; engine idle is erratic, doesn't return to 600 rpm when you come to a stop? Basically, whatever the ECM controls will not function as it should.
Since I replaced the ECM, my 89 runs like new. Everything works like it should; even the tranny (auto) shifts like it should.