edco

I have a hard warm starting issue “not leaky injectors” The car starts fine when cold, but after reaching operating tempter and sitting for 30 minutes or longer it is hard to start. It always starts but you have to crank it for 15 or 20 seconds. It cranks at normal speed. Once it starts you can shut it off and it will start right up. Yesterday I drove to lunch and it sat for an hour, it was hard to restart. When I left work it again was hard to start after sitting for 2 ½ hours car was still a little warm “Temp Gauge showed some heat ”.

We thought leaky injector so I sent the injectors out to be cleaned at WitchHunter Performance. That didn’t solve the problem so I changed the fuel filter & check valve. Same problem? Both Bill Ball and I thought it still looked like a leaky injector problem. So I asked Gordon at WitchHunter to take a second look at the injectors and check for a leaker the report came back that they were all ok.

What do you guys suggest to look at next? Could this be vapor lock or is fuel somehow draining back to the tank and leaving the rails empty? Any help would be appreciated. I have had the car for 7 months and this has been an on going problem from the get go. Thanks in advance for your help…

88 S4 5 speed
139K miles

Thanks

Charley B

Do you have a fuel pressure gage available that you could slap on the rail to see if there is a fuel issue there or not? The fact that you can shut it off once it starts and then start right up again sure makes it sound like a fuel problem. Have you tried a shot of starter in the intake?

IcemanG17

Matt
Check the resistance on the Temp II sender.....but that tends to be more of a cold start problem....another common hot start problem is the fuel pressure check valve? (or something like that) in the trunk by the fuel pump?

edco

Hey Guys,

Charley,

Bill is going to help me check the pressure at the rail. I haven't used starting fluid, as at this point it's more of a nuisance type of thing.

Brian,

I checked the resistance on the Temp II sensor and it looked good all with in specs, I have not tested it when the car is hot, and perhaps I should take a look at that as well. I did replace the fuel check valve in the rear at the pump.

ZEUS+

Sure does sound like the check valve in fuel pump. Fuel pump mounted on fuel tank under panel.

Mrmerlin

Hi the check valve is screwed into the end of the fuel pump and one of the lines connects to it. this can be replaced. i had a similar situation hard to start when hot I replaced the temp 2 sensor and i also replaced the plug as the internal wires had shorted together still the same problem I then replaced the fuel injectors with a set from fiveO motorsport about 220.00 bux (the only thing I had to change the injector O rings as they are made to fit a ford fuel rail so new O ring were needed) these are the 4 hole spray type and they are the 19lb injectors after this the car starts right up hot or cold, . For your problem you might want to check the vacuum damper/fuel pressure regulator on the fuel rails make sure they are not leaking fuel into the intake, and try cleaning the mass airflow sensor be very careful the thin wire can break if you hit it with too much spray pressure

ZEUS+

My post was a littlte late. Well, you got the check valve covered. Good start. After you test fuel system, regulator and dampers etc. If everything tests fine and holds pressure, possible mafs. Could be a weak relay that cools down.

edco

Hey Mrmerlin

I had she same problem with the plug going to the Temp II sensor and have changed it out. I also had some shorts in the harness for the fuel injector plugs “In the rubber boot near the plug” Each time I hope I have this little gremlin fixed

The check valve has been switched out as well, I would think a bad check valve would effect both warm and cold starting. Mine starts right up cold, even after sitting a week or two…

Mrmerlin

Ok so if you can swap out your MAF with a known good one and this makes no difference then I would try the new injector route, that is also based on the dampers being good The check valve is probably not the problem but a fuel pressure gauge fixed to the fuel rail will let you know . Other possibility is to try to hold the gas pedal to the floor when its hot see if this makes a difference. And further thinking look for any vacuum leaks also try cleaning the ISV with the wd40 sprayed into the vacuum line

Bill Ball

From the symptoms, we were almost certain that was either a leaky injector or two or the check valve, so we did both, including the injectors twice, as Matt reported. It still could be either of those. We do need to put a fuel pressure gauge on it.

Matt, I have a spare gauge we can mount on your rail. If you have any time, bring the car by tomorrow or on the first. It will only take a short time to mount it...after the engine cools a bit. Let me know.

Stan, we haven't looked at the dampners, but I would expect them to cause other problems if leaking. I suppose this could be a goofy MAF response when it gets warm, but again, I would expect other driveability issues than just hard warm starting. The intake was removed and all the lines redone, as well. We need to double check that.

The symptoms are so classic for leaky injectors that maybe my vision is being narrowed too much. However, if we block off the fuel return and the fuel pressure falls when the fuel pump is turned off, then leaky injector it is.

Mrmerlin

Hi Bill I had a similar problem and after installing new 4 spray injectors the car fires up right away hot or cold I would do the other checks first before removing injectors

fabric

Here's all the stuff I checked for my warm start/idle problem:

http://members.rennlist.com/fabric/i...eshooting.html

My problem was very similar, except that it took 4-5 starts of the car, and each time the idle was wildly fluctuating. Turned out to be the LH. If the car is driving fine otherwise, if you can get your hands on a good LH I'd try that before the MAF.

Bill Ball

LH....that would be nasty, but I guess it has to be on the list even though hard start warm apopears to be the only symptom.

I think we ran the Spanner on it before. We will run again, rule out everything else with fuel pressure gauge, etc. We can swap my MAF and LH into Matt's car.

edco

I’m headed over to Bill’s to check to the pressure in the fuel rail, as well as some of the other suggestions Will let you all know what we find, thanks for all your help and suggestions…

Bill Ball

Matt just stopped by. We put on the fuel pressure gauge. The pressure fell to essentially ZERO in about 15 seconds after killing the ignition. That would be SOME leaky injector(s), if that were the cause. Both dampners and the fuel pressure regulator hold vacuum and there is no gas in their vacuum lines. I clamped the fuel supply hose at the tank as soon as Matt killed the ignition, and the pressure still fell exactly the same. So, it is not the check valve. Just for fun, we swapped in my LH - no change.

Anyway, according to the WSM test procedure for hard starting when warm, we needed to check the return from the fuel pressure regulator by detaching the fuel return line and seeing it leaks fuel with the engine off as the pressure drops. BUT the fuel pressure drop is so fast, there is no way to test this unless we somehow block off the return. The return hose at the firewall didn't look flexible enough to clamp. We should have pulled the access cover off the top of the fuel tank to expose the return hose there and clamped it. I forgot that that is where the return runs into the tank. Oh well.

Anyway, based on our observations we are going with FUEL PRESSURE REGULATOR. It's not the check valve. It's not the injectors as there is no evidence of flooding at all, and this is just way too fast a leak. Here is the WSM test procedure we would have liked to have followed to verify the FPR. So, the FPR is capable of performing regulation but will not hold pressure and allows fuel to go out the return line fairly quickly.