Cold-startup, engine hesitates like fuel is getting cut or running on 3 cyl..then OK

[achtunge30]

Tried AFM first, no difference.

The car starts up fine in 3-5 cranks. Then I put a little load on the engine to start moving then it seems as I get a huge drop in fuel pressure and the engine struggles big time...if I let off the gas and go to neutral, the idle will be 550-650RPM, I have to rev it out and it'll be stable at 750-800RPM.. (already cleaned the ISV).

To recap what I've checked, i made sure all the hoses didnt have any "hissing", checked all my intake manifold bolts and made sure everything was plugged in. I replaced my o2 sensor, tried another buddy's M42 AFM. The fuel pump and relay are both a year old. Fuel filter, plugs, wires, are also within 1-2yrs old..I pulled all the plugs, the center 2 plugs have a lil oil on them so I retorqued the valve cover bolts again. All the vacuum lines are new as well.

Other than that, I am lost.

[NC325iC]

i had that same problem a while ago, unsure if its still there or not as i havent been able to drive my car in over a week, but all i did was clean out and adjust my tps.

my car would do it on any startup, and i would have to rev it up to 2k for a little while before it would be ready to go again, come to think of it i think that was due to my o2 sensor warming up.

[achtunge30]

how did you clean the tps? tb cleaner? brake cleaner?

[kowalski]

put a 10$ inline fuel guage in. then see if it holds pressure after you shut it off. if it is dropping to 0 then the FPR or the fuel pump check valve is faulty. You can test the FPR by pinching the return line when you shut the engine off. If the pressure drops it is likely an $11 check valve. i can get the pn for you if this is the case. If the pressure does not drop then the FPR is at fault.

Does this mean you have the hard start problem? I recommend you try jumping the fuel pump relay before starting the engine in order to pressurize the fuel rail when you usually experience the hard start to rule it out… while it is a cheap, simple solution there are a number of other issues that show the same symptoms. One typical issue on the M42 is the ‘flying saucer’ check valve ($63 part number 11157501567) for the PCV system if the engine is also running rough and is difficult to start, especially when cold. To rule it out pinch the hose off when the engine is warm… if the idle smoothes out that’s it… the base seal can also leak so try some butane, propane, or ether at the base to see if the engine smoothes out.

also check crank sensor gap, and crank sensor resistance, both hot and cold. a new sensor cold is 960 ohms +_ 10%

[Intense]

put a 10$ inline fuel guage in. then see if it holds pressure after you shut it off. if it is dropping to 0 then the FPR or the fuel pump check valve is faulty. You can test the FPR by pinching the return line when you shut the engine off. If the pressure drops it is likely an $11 check valve. i can get the pn for you if this is the case. If the pressure does not drop then the FPR is at fault.

I suspect I have the same problem. My car is difficult to start and bogs miserably after it is started for a minute or so. After that, it's fine.

I'm thinking it's the FPR or the aforementioned check valve. Can you dig up the part number on that check valve? Is the valve mounted on the fuel pump?

thanks

[mangomango]

Mkay. to dig up an old thread but my car is having the exact same issues as the OP's but there are no answers in this thread.

I did mess under the intake, rebuilt injectors and new timing chain components. (note it did not have these issues before all that work)...

however the little hose that was connected to thing on the fuel rail was not connected to the throttle body.... and i reconnected it after all work was finnished

so as stated the car does everything that the OP's car does upon first start up. If I shut it off for and restart 1 min later its fine and has no issues. If i start it 10 mins later it has the issues.

[seth m42]

mine did something similar to this. with mine it was a half rotted away lower intake manifold gasket.

[mangomango]

i replaced all the intake gaskets. I undid the little hose from the fuel pressure reg to the throttle body and that made it run worse but the car still has a fuel supply problem after starting. Once it gets going which usually takes me flooring it while there's a load on the motor (revs spotty with no load) a couple times to get everything "cleared out" and then it drives fine. Plenty of power.

however once the car is running normal when the rpms come down after pushing in the clutch they like to dip down to maybe 500rpm and then come back up and settle at 750ish.

when I turn the key to the on position before starting the fuel pump only primes? for a half second... shouldnt be longer or am is that normal?

[mr ilia]

Check spark plug wires, spark plugs, ignition coils. Could be sticking injector.

Sounds like something needs to "warm up" before starting to work normaly, very likely an electronic component.

[mangomango]

Okay if i let the car run for 5 mins from a cold start before going anywhere, it seemingly runs fine. however if i get to where Im going and get some milk from th store and come out 10 mins later, start car and make way home it does this horrible bucking and not idling good. if i hold my foot still on the gas while moving, say 10 mph in 1st gear it will actually feel like it running out of gas. and the rpms will drop until i push the clutch in and let off the gas. I have no idea what is going on here.

Ps. The injectors i put in were rebuilt my a forum member here. but the ones i pulled out were the better 4 pintle mustang injector. but they are pretty dirty and one of them leaked. Would like to get them rebuilt but have no idea where to have them done.

also visually checked coils and wires for defects but found nothing unusual.

It also has an issue when it settles back to idle after pushing in the clutch. itll dip to 550 rpm and stay there till i give it a bit of gas then its fine. or it will randomly climb to 1200 rpm after i give it a bit of gas to get it up from 550.

I also unplugged the AFM while the car was running and from a cold start and the car just died. no sputtering just died. Don't know if any of this is normal

[mangomango]

Update....

Turned out I plugged in the wire on the fire wall when doing the mess under the intake.

Unplugged wire, and it runs great.

Hope this helps someone in the future.

[kwill22]

just fyi, its a good idea to let your car run for a couple minutes after a cold start before you drive off anyways.

[16v of E30]

i just did an italian tune up on my 293xxx km m42 motor. idle issues were always happening, so i threw in some octane booster and ran some 94 from the pump. after i left the station i pulled up to the lights on the highway and ran it to the redline in 1st-3rd gear, holding at the redline for a couple hundred feet extra, then proceeded to drive an hour and a half to the city. new plugs oil and she has never run better. all issues burned out the back of the tail pipe. seafoam is good too...

[mangomango]

Letting a car run for a couple minutes is useless unless its below 40 degrees outside. Once its fired and running its circulating oil and everything else. Thats why they have dual viscosity oils right? Not to mention the transmission fluid isnt getting any warmer just sitting there anyways.

However I always take it easy for the first mile or so anyways.

[omera60]

Update....

Turned out I plugged in the wire on the firewall when doing the mess under the intake.

Unplugged wire and it runs great.

I hope this helps someone in the future.

I know it is a very old thread but I am having the exact same symptoms. Which plug was this? Do you happen to have a picture?