Author Topic: What could cause a hesitation / timing pull right after start-up? (Read 3436 times)

achtungE30 · « **on:** June 07, 2007, 08:04:15 AM »

*EDIT*

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.

Other than that, I am lost.

gearheadE30 · « **Reply #1 on:** June 07, 2007, 07:52:01 PM »

Sounds like a bad AFM motor or sensor, but I've really never heard of this before.

achtungE30 · « **Reply #2 on:** June 18, 2007, 09:20:20 AM »

OK soo now...

I've got new o2 sensor, have cleaned the tank twice with chevron techron and some BMW stuff my mechanic gave me that "exceed BMW lifetime limits on fuel injectors", cleaned ISV and swapped AFMs, switched back to factory airbox, retightened all bolts on the valve cover, checked my plugs (found 2 center plugs had a lil oil on them , so I retorqued the valve cover bolts (gasket replaced last year)...i'm not pulling any codes apparently but now the hesitation only happens initially after a startup when cold, or if the car sat for 10 minutes off.

What else??

I'm thinking fuel - however, I replaced the fuel pump last year when I got the car, also replaced the fuel filter a little before. Since then I've put around 15k on the car. I'd like to test fuel pressure. How do I get to the fuel rail test port to hook up a test gauge? Maybe its the FPR? I don't smell any fuel leaks near the injectors though and glad I don't!!

bmwman91 · « **Reply #3 on:** June 18, 2007, 10:22:14 AM »

The part-throttle stuff was definitely the same problem I had last year. It was a shot AFM. After the MAF swap, that issue went away.

Now, I DO get the near-stall on a cold start if i do not blip the throttle a couple times after starting. It only happens when I load the motor trying to get going. If I stay on the gas during the issue, it will stall. If I get off it and push in the clutch, it does not do it again until the next cold start.

Is that what happens to you? It is friggin weird, I have checked every input sensor to no avail! It is annoying!

achtungE30 · « **Reply #4 on:** June 18, 2007, 12:53:52 PM »

Quote from: bmwman91;27979

The part-throttle stuff was definitely the same problem I had last year. It was a shot AFM. After the MAF swap, that issue went away.

Yes, the o2 sensor fixed that one!

Quote from: bmwman91;27979

Now, I DO get the near-stall on a cold start if i do not blip the throttle a couple times after starting. It only happens when I load the motor trying to get going. If I stay on the gas during the issue, it will stall. If I get off it and push in the clutch, it does not do it again until the next cold start.

Is that what happens to you? It is friggin weird, I have checked every input sensor to no avail! It is annoying!

That is my current issue now - still trying to figure this out.

bmwman91 · « **Reply #5 on:** June 18, 2007, 03:19:04 PM »

Well, at least we can rule-out the air meters since we are using 2 very different ones.

All I can think of would be the TPS being worn (checked mine, it was OK), the FPR sticking, or umm not poking the squirrels enough to get them fully awake?

achtungE30 · « **Reply #6 on:** June 18, 2007, 03:21:00 PM »

I thought about the FPR, but wouldnt that show itself in all instances of driving and not just when starting off from a cold-start? To replace the FPR would mean to take the upper manifold off first?

Where is the TPS and how do you check it?

bmwman91 · « **Reply #7 on:** June 18, 2007, 03:25:03 PM »

The FPR is a little bit of a long-shot, you are right. I dunno, maybe it can sorta settle and get stuck when it sits cold? It would explain why it bogs on the first demand of higher pressure.

The TPS is the little black plastic thingy on the throttle body. It has a connector with 3 wires on it. Pull the connector and get a multimeter on the middle pin and any of the outside ones. Move the throttle by hand, and it the resistance should change linearly with no sudden changes. If there are sudden changes in resistance, you have a bad TPS...but this would also be causing constant issues I think.

achtungE30 · « **Reply #8 on:** June 18, 2007, 10:39:43 PM »

Well drove the car just around my complex tonight - just putting along, it ran fine - but when I gave it, oh about 25% throttle, then it began to bog. I almost was about to say it doesnt happen EVERYTIME but ugh...