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Message |
    
Mike Rupp (Mike_Rupp)
| | Posted on Monday, April 29, 2002 - 09:39 am: | 
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Periodically, for the last couple of months my '97 Disco starts with difficulty. It would crank over well, run rough & stall maybe once or twice and then all was well. The last couple of days, though, the same thing was happening, but the engine would run extremely sluggish for a minute or two and then it would seem to be fine. After the engine warms up, it starts fine and runs fine.
Here are the things I've done recently:
Optima red battery
Magnecore wires
NGK plugs
fuel filter
After searching the archives, I've come up with some possible solutions to somewhat similar problems:
Engine coolant temp sensor
Fuel pump relay
Fuel pump
Injectors
Does anyone have any ideas where I should start? I don't want to just replace parts and just hope that it solves the problem.
Thanks in advance,
Mike Rupp |
Moe (Moe)
| | Posted on Monday, April 29, 2002 - 04:11 pm: |
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Mike, another place to look would be the stepper motor. I cleaned mine for the second time last week, plenty of crud builds up there. Mine will need replacement shortly.
When you turn the ignition on (without turning starter) do you hear the fuel pump work for some time and then cut out once pressure is reached?
Best of luck |
Mike Rupp (Mike_Rupp)
| | Posted on Monday, April 29, 2002 - 04:53 pm: |
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When I turn the ignition on, I hear a quiet, quick thump, which I assume is the fuel pump turning on. I can't tell if it stays on though.
I'll check the stepper motor, although I didn't think that it was it, only because once the Disco is finally running well it idles fine.
From some of the old posts, I think that it might be a leaky injector, which would seem to explain why it runs rough for a short while and then clears up. I'm guessing that the leaky injector fouls the plug, and I'm running on 7 cylinders for a while. |
Jon Williams (Jonw)
| | Posted on Tuesday, April 30, 2002 - 09:06 am: |
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A lot of problems can be traced to a faulty coolant temp sensor. To check it, cold the resistance should be about 8000-12000 ohms. As the coolant gets hotter, resistance goes down to a few hundred ohms. I've heard that the best advice is to always replace the coolant temp sensor first, as they are usually the root of all evil  They're under $20.00 anywhere except the dealer, so that's not a bad idea. However, a dirty mass airflow meter element can also can cause cold starting problems (which I'm sure you're thrilled to hear, given the cost of those boogers). A feature of the Lucas Hot Wire (Bosch LH-Jetronic) injection system is to briefly heat the airflow meter element to about 1600°F after shutdown to burn-off accumulated dirt. After while, this doesn't work as well because the element either burns-out, or the whole meter goes bad (which isn't uncommon). So the "hot wire" can't clean itself effectively, and that sends the ECU a false signal. Certainly, check the injectors, but they usually are not at fault. Among things to be wrong are a faulty ground at the injector. During running, the injectors are "hot" all the time, and they fire when the ECU grounds the bank for the duration of the injector pulse. So, a whole bank (4 injectors) would be affected if even one injector were faulty. To tell if injectors are at fault, you have to check the injector pulse width for each bank and make sure they're kinda equal. Just some stuff to think about... |
Mike Rupp (Mike_Rupp)
| | Posted on Tuesday, April 30, 2002 - 09:52 am: |
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Here's more to the story: last night I bought a fuel pressure tester. With the ignition on (engine not running) Fuel pressure = 20psi. With the engine running I get a fuel pressure of 30psi. I'm pretty sure that it is a fuel system problem, maybe a leaky injector.
Any ideas? |
Jon Williams (Jonw)
| | Posted on Tuesday, April 30, 2002 - 11:56 am: |
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Yep. Fuel pump should pressurise the line fully at key-on, engine running or not. The pump has a cold start check valve that sometimes goes bad. Never replaced one, don't know if you even can on the Rover pump... |
Mike Rupp (Mike_Rupp)
| | Posted on Tuesday, April 30, 2002 - 12:41 pm: |
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Jon:
Just so I understand things better let me ask a couple questions. Let's say the fuel pump is ok, if it is running 20psi(which is low) could a leaky injector explain the lower pressure?
If the fuel pump is bad why would it the system be at 30psi with the engine running?
I'm just trying to get a handle on why the truck runs terribly for about 45-60 seconds and then it seems to clean it self out. Seems like its flooded and then cleans out.
Thanks in advance,
Mike |
Jon Williams (Jonw)
| | Posted on Tuesday, April 30, 2002 - 02:50 pm: |
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It can, but that usually doesn't happen. Unfortunately, the only way to check for a leaky injector is to check each one, removed. A shop is best suited to something like that. Unless the injector armature is bad and the thing is sticking open, you wouldn't be able to tell much listening to them. Luckily, Bosch LH-Jetronic injection has been used on about every European car from Audi to Volvo at one point or another, so any shop specializing in them could easily help you there.
Even though the pump may work well enough, it may not be holding residual pressure. Here's a simple test to rule-out fuel pump woes: connect your pressure gauge to the Schrader valve on the fuel rail with the engine running. Pressure should be 30-35 psi, ideally 34 psi. Turn the engine off, leaving the pressure gauge connected. Your residual pressure should stay around 30-32 psi for at least 15 minutes (engine hot). After sitting a while your residual pressure shouldn't drop below about 27 psi. If pressure falls to 0 instantly or at all, your pump check valve is bad; replace the pump.
What keeps hinting fuel pump to me is the low starting fuel pressure that increases as things "warm-up." 20 psi is insufficient for the engine to run in any case (as you well know), and even 30 psi is not great, but it is acceptable. One injector alone stuck open would not cause a 10 psi loss in fuel pressure. Supposing one was, it likely would not close again. A whole bank of injectors, however, maybe could cause that kind of pressure drop. In that case you have a problem lying with the ECU. $$ With the LH-Jetronic system, at start-up the injector pulse width is usually tripled. But that pulse tune is triggered by the ignition circuit, and changes to idle tune when the ignition is released. Even then, 20 psi would hardly deliver enough gas to start your engine, much less flood it.
Beyond that diagnosis, if you have an oscilloscope I can tell you more, otherwise it won't do you much good for me to spout-off scoping a fuel pump |
Moe (Moe)
| | Posted on Tuesday, April 30, 2002 - 08:30 pm: |
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Jon, that is great information. I hope it helps Mike out, and I'm sure I'll use it in the future. |
Mike Rupp (Mike_Rupp)
| | Posted on Tuesday, April 30, 2002 - 11:46 pm: |
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Jon - Thanks for the info. I'm sure that I'll be getting a new fuel pump in soon.
I'll let you know the results.
Mike |
jerry quintana, co springs
| | Posted on Wednesday, May 01, 2002 - 02:46 am: |
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i am having the same problem cold starts. also i have a bad idle problem. 1995 discovery. the dealer ahs had it for the past week and cant figure the problem out. i have to let the fuel pump stop puming before it will start they have checked every system on the vehicle and nothing. everything from the fuel pump to the exhaust check out good. no codes from the computer they are stumped i guess the only good thing is that they gave me a 2002 loaner for free. dam that thing rides smooth. waht did they do to the suspension? |
Rob Choromokos
| | Posted on Wednesday, May 01, 2002 - 10:41 pm: |
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Mike,
Don't forget the fuel pump relay will kick out the fuel pump in the event of a non-start (ignition on) condition after 3 secs. If the fuel rail is starting at 0 psi, the 3 secs will probably only get you to 20 psi with the ignition switch on. Try turning the ignition on/off a few times and I bet the pressure will build to the 30 psi that occurs during a running condition. Someone mentioned a check valve in the fuel pump, I'm not aware of one, unless you mean the pump is backflowing for some reason - not sure it can. Pressurize the system to 30 psi and clamp off the fuel pump at the fuel filter with a pair of visegrips (protect the line of course). This should tell the story on the fuel pump.
robc |
Bill Molnar (Circekat)
| | Posted on Thursday, May 02, 2002 - 08:00 pm: |
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I just went thru my fuel system. Pump has a cup around the impeller body, returned fuel goes straight back to the impeller cup. On the back of the air inlet on the top of the engine, there is a fuel pressure regulator. It has a vacuum line that attaches to the air inlet housing. It would seem possible that the pressure regulator might be malfunctioning, although I would be inclined to check system integrity by clamping off the fuel return line, turn ignition on and then clamp fuel to engine after the fuel pump relay kicks off. This would be easy at the fuel pump itself. If pressure holds, then release the fuel return. If pressure still holds, it would be my guess that the pump check is not holding. BTW, Series 1 fuel pump is $221.07 at dealer, $219.95 at Atlantic British (esr3926). |
Mike Rupp (Mike_Rupp)
| | Posted on Friday, May 03, 2002 - 09:49 am: |
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Rob:
Tried that. The results of pressure checking have actually deteriorated. No matter what I do (cycling the ingition switch), I can only get about 20psi, even with the car running. The pressure gauge needle is bouncing around from 15psi to 20psi. Sounds to me like the pump is nearly dead.
I just ordered a pump from Nathan Crabtree for much less than the dealer or AB price. I'm about 95% sure the pump is to blame. If not, back to the drawing board. |
Mike J. (Mudd)
| | Posted on Friday, May 03, 2002 - 10:10 am: |
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What about your thrrmostat?
have you tested it? replaced it? that can cause similar problems. |
Mike Rupp (Mike_Rupp)
| | Posted on Friday, May 03, 2002 - 10:47 am: |
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Mike:
I've thought of the engine coolant sensor as a possible culprit, but first things first. My fuel pressure is much lower than what is supposed to be. Therefore, it has got to be something in the fuel system (pump, relay, regulator, injectors)
At least for now, I've ruled out injectors because once the car is running it seems to be fine. If the fuel pressure problem was related to the injectors, I doubt that it would run well at all.
That leaves me to the pump, relay, and regulator. I theorize that the pump is the most likely problem. When that is replaced, and if the pressure checks out ok and I still have problems with starting, I'll look to other causes. |
Mike Rupp (Mike_Rupp)
| | Posted on Friday, May 10, 2002 - 09:08 am: |
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Well, I installed the new fuel pump last night and everything checks out ok. I get about 36psi with ignition on, engine off, and 30psi with engine running. Also it holds pressure after shutting engine off.
Thanks everyone!
Mike Rupp |
Rob Choromokos
| | Posted on Monday, May 13, 2002 - 05:26 pm: |
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Mike,
I have been having the exact same problem as you as was hoping you would get to the answer. My pump was acting up this Saturday and finally left me nearly stranded on the expressway. Limped home and replaced my fuel pump today and everythings back to normal.
Thanks for the help......
robc |
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