This is sort of a continuation of my earlier thread. Charlie V and some others were/are helping on. First 2003 Land Rover Discovery II V8 with 125,000 miles on it.
First, when it's cold it starts right up, idles at 750 rpm, runs fine. No issues with power, gas mileage, surging, or transmission shifting. When I come to a stop light it idles at 750 rpm with no problem.
Problem. The problem occurs when it gets warm/hot (temp gauge dead center) after driving around town etc. Once I shut it off and try and restart it one of two things happens. Either it starts and the RPM's jump to a bit over a thousand then suddenly dies or it starts and the RPM's go to 750 then drop to 500 (sometimes the oil light will come on for a second the dissapear). If I hold the accelerator on for a bit it will settle down and drive fine just like stated above. It is a starting issue when hot/warm.
Recently it was at the local LR dealer and they replaced the spark plugs, new wires, and a coil. They also put new gaskets on the valve covers. After discussing it with Charlie V and my local mech I felt good about putting a new IACV on (Bosch). Did that with no relief. I also have a new MAF sensor coming.
My thoughts (I am not a mech just trying to use what I have read on the forum and some common sense). I don't think it would have anything to do with the new wires, plugs, and coil since when it is running it runs fine. Certainly wouldn't think it was valve cover gaskets they replace. I was really hopeful the IACV would do the trick. I am not holding out much hope for the MAF lol. From what I have read some people do have problems with the CPS when it gets hot if it is about to fail. From what I have read the TPS would cause noticable driving issues which aren't present. Also mentioned was the possibility of a fuel pressure when it gets hot. I know the fuel pump is working since it doesn't bleed down during the night and starts just fine when cold.
SOOOOO any thoughts would be appreciated. Thanks in advance for taking the time to read this.
Doc McCoy (HMCS SARC Navy Ret)

Oh and most importantly it has never thrown a check engine light or code of any kind.

 

I don't think CPS by itself can make rpm go higher or lower, it just provides information for ECM,,,,, however ECM is responsible for engine operation & fuel mixture & basicaly how engine should run,, & it gets its info from lots of diff sensors including MAF & O2 sensors,,
But how could you know which sensor is not doing its job, one way is to change all sensors & hope one will fix the problem, (too costly),, better way to have a good scanner & monitor the way O2 & other sensors output,, but that was the job for dealer , & they have the best scanners, & should have done it for you,,, didn't you pay them to fix the issue you were having,,, I would go back to dealer & tell them even after they replaced the parts they did, issue still exists, & have them fix it,, or at lest find out what real problem is insted of them just trowing parts at it, & hope it gets better,, (they can easily check to see if O2 sensor or MAF is working properly b4 replacing them,)

 

No the issue that it went for was that it had a hitch while driving. Sort of a bump in the force if you will. Since they probably never drove it far enough to get it hot they would not have seen the issue. When I picked it up of course it was cold and started fine and ran the whole hour and a half back home just fine. The bump in the rpm's had totallly gone away so they did fix what I brought it in for.


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The hook up a good scanner & check if O2 sensors operate properly (or have dealer do it), b4 replacing them,,
CPS in other hand, either works or dies, without trowing codes, but will not make rpm go up or down, it's job is to tell computer when to send spark to cylinders,,
MAF (if bad) can do what you described, also any kind of vaccum leak could do same if, sometimes cracks in vaccum hoses , etc , can become more obvious as engine temp goes
up,,,

 

So would you consider just replacing all the vacuum lines. I know it would be a needle in a haystack trying to find the one that was bad?

 

You can check all of them one by one b4 replacing also look for loose connections, I would hold one end & suck the air out from other end & see if each line holds vaccum, then replace the bad one,, but yes you can replace all if you want, (then again they all could be fine,,) also check vaccum line connections , they could be loose or cracked,
Since dealer replaced valve cover gaskets, & coils , I suppose they replaced intake gasket as they removed it , so that should not have any leaks (in theory)

 

Doc, I was reading through what you wrote in this post and I think I should make my point about fuel pressure more clear. What I was talking about is, fuel needs a certain amount of pressure to keep it from boiling and causing vapor lock when the engine is hot.
The fuel system on these trucks isn't particularly high pressure to begin with. If you start to lose a little pressure, you would never notice a difference as far as starting and driving. The system primes when you turn the key on. So you probably wouldn't notice on a cold start. However, if the fuel boils in the rail and it vapor locks, you're going to have a hell of a time getting it restarted.
Like I said before, in the other thread. There's no way to tell for sure without doing a pressure test.
I hope you get this figured out soon. Please post what you find.

 

Disc i have seen someone post on here that before starting it turn the key on and off three times. I think this was checking a fuel pump issue. Would this help isolate my problem even if it only does it when hot? What the hell next time I drive it and it gets nice and warm I will try before I start it and see what happens. Can't hurt lol

 

That may help build a little more pressure but if it's already vapor locked it may not help the hot starting issue.
The best way to diagnose a fuel pressure problem is with a gauge. That way you can test the prime, rest, running and rev pressure. If it's under spec, has no or low rest pressure or pressure drops when you rev the engine, you need a fuel pump.
I started out with a $20 fuel pressure gauge from Harbor Freight. They're not the best but they do work and are well worth the money.

 

Just an update. I have replaced the IAVC and the MAF sensor with no results. My mech said since he replace the CPS less than a year ago and it was still under warranty he is going to replace it for free. He will check the pressure on the fuel line as well. I don't expect the CPS to fix the problem. I am also going to replace the TPS. The reason for the later two is simple. When or if I take it to the LR dealer it's less parts for them to try and replace and bill me for. My price for the parts above is way less than what they would charge and I don't charge myself labor lol. I will keep you posted on what Daryl (my mech) finds about the pressure. Thanks Disc.