Full throttle hesitation
 

The car is a E320 1994 104 engine, and the problem is when i give full throttle at a stop sign the car stumbles a few seconds and then take off. When giving full throttle normal speed the car hesitate and jerking. This happens during the summertime and not in the winter i suspect the air mass sensor but when I disconnect the cable to the air mass sensor there is no difference in performance. If there is a throttle position sensor the problem should be in the winter too. The wiring harness is brand new. I will also check the ECT sensor.

Fuel pressure, fuel pump volume, & mass air flow are the keys for full throttle acceleration.

Testing the fuel pressure & volume would be a good starting point.

Assuming the air & fuel filters have beed replaced.

Well, doesn't your MAF test indicate a bad MAF? Disconnected, there's no difference in performance, meaning that when it's connected, it's not doing anything. What am I missing?

there is no change in performance when I disconnect the MAF the full throttle hesitation is still there i was expecting the hesitation would disappear if the limp mode cut in, but at first the was no idle when i disconnected the MAF.
The fuel pressure is ok but I have not tested the fuel pump volume.
I also got new spark plugs and spark plug wire and no air leak what I can see.
Yes the air filter and fuel filter is replaced

What I was saying was that if the MAF were good, disconnecting it would cause engine performance to degrade. But since performance showed no difference when you unplugged the MAF, it seems as tho the MAF is not doing its job. This happened on my good wife's Maxima not long ago. Very similar symptoms of terrible WOT performance. I unclipped the electrical connection at the MAF with no difference. Replaced the MAF, she's happy again (both the wife and the Maxima).

You problably right since it's no problem in the winter weather that was my first thought, but since the MAF is so expensive in my country i guess thats why I hope there was another problem.

M.B.DOC, Just curious --would it be possible that pressure is on spec, but volume is not? Or are they both directly related to each other.

Thanks

Pressure can be great at idle, but volume suffers easily with filter and tank-vent problems.

I agree

Always do a flow test when doing a pressure test..specially where the complaint/condition is at a a time-frame when high fuel consumption is demanded. [ Like WOT or heavy engine load condition]

A quicky in-situ drive test is to drive up a decent graded hill with max load on the engine w/o downshifting..low volume will show up quickly under those conditions...[ as will weak plugs/ign]
A 'T' in a pressure gauge will get you volume and a trick is to use a clear line on the flow test b/c you can then see any air in the line as you do the flow test. The old benz gauges actually had a glass tube as part of the gauge so the Tech could monitor for possible suction side air when doing a flow test.
I just put a loop in the clear line and if there is any air , it shows right up..
Then yu check lines and clamps, specially pre-pump.

Arthur Dalton can I do a volume test to the Schrader valve in the fuel rail?

Yes

You can do it w/o a gauge or with a gauge that has a "T" for that purpose..many FP testers come with a flow port. I just made my own and anyone can by just making a T in the fitting line for the gauge ..then you can do both at the same time.

It is smply to see if you have a good flow.
As some guys have stated, you can have a plugged up filter that will get you spec pressure at a gauge , but the flow rate can be way off b/c a pressure reading does not equate to a good flow. And a good flow does not always mean you have a good/high enough pressure.
If engine demand is higher than the flow rate, the fuel volume can not keep up to the demand.

[ i.e. if you had a kink in your garden hose , you can still have pressure at your nozzel, but as soon as you opened it up full blast .. you could have very little flow rate. Once you turn the nozzel OFF, the low flow rate will allow the pressure to build up again in a short time, but you still have NO VOLUME., as in a partially plugged filter. Another example would be filling a 5 gal bucket up with a small dia hose and a large diam hose that both had the same pressure..which is why they don't use garden hoses on the Fire Trucks ..;)
Your fuel system needs BOTH..and no air in the feed line.

Thanks Arthur I have a pressure tester with a flow port so now I now how I can easily check fuel volume.
I guess I do the test with ignition on or should I have the engine running?

Cool ..that is what most of the new ones have..and the clear plastic line suggestion can be usen on any flow procedure to check for air bubbles... just like one would use on a brake bleeder line..clear lines for flow observation is just common sense stuff..........unless you have Xray vision...Mine is weak now...ever since I had that bout with the Krytonite....bad...
Can't do the Tall Building gig anymore either...the Grandkids keep asking, " Com'on Granpa , jump over that tall building like you said you used to do...Kids ..they just don't Understand !!! I havn't seen an Enclosed Phone Booth in Years.

Fuel pressure and fuel volume seems good and change the MAF but the problem still there. Can't find any airleak and the problem seems to be much bigger when it is hot outside. The ignition cables are changed.

I'm wondering if the ignition coils are weak, but don't know how you'd tell. Are they original?