TugboatTony Posted October 15, 2011 Share Posted October 15, 2011 I'm having a helluva time with my 95' SE. I've changed everything in the ignition system, checked it all twice. good compression in all holes, all filters have been replaced, (the fuel filter twice) new O2 sensor, new coil, cleaned and tested all connections, cleaned and tested the MAF and the TPS. The distributor and crank sensor are fine, and the timing is perfect, all of the injectors are working and code 55 on the ECU after numerous checks........yet its still BADLY hesitating under load. I can rev the piss out of it in park or neutral and it wont miss a beat, yet driving it and touch the pedal once its warm and it'll bog right down 'til it nearly stalls. I've just done a fuel pressure test on it and it runs between 30 and 35 psi but it'll start to bog out under load and drops to nearly 20 psi. I realize this is a fuel pressure issue but is it the pump or something to do with the ECU telling it to 'chill out' on the fuel draw because of an external problem? Link to comment Share on other sites More sharing options...
sewebster Posted October 15, 2011 Share Posted October 15, 2011 Maybe your fuel pressure regulator is screwed up? But it doesn't really sound like it. FSM test is that the pressure should be 34 psi at idle, and 43 psi with the vacuum hose disconnected. And the more vacuum, the lower the pressure. Probably if the pressure can't stay high when you are sucking a lot of fuel then the pump can't keep up. Or your filter is clogged Link to comment Share on other sites More sharing options...
krmiller07 Posted October 15, 2011 Share Posted October 15, 2011 (edited) I know it sounds stupid, but is the fuel filter on the 'right'way? I'd also check the condition of the fuel lines and make sure none of them are collapsing, kinked or obstructed. It is possible you have a bad fuel pump. This happened to me a few years ago. I went through 6 'good fuel pumps' before changing brands, and settled with a Bosch fuel pump before the same problem you described was corrected. My truck would idle for as long as I wanted, however under 'load' or driving it would stall out and quit at exactly the same place while driving up the road. It was running the lines dry under load, but idleing it was fine.Stay away from the Airtex and AC Delco replacement pumps. I wouldn't recommend a Nissan pump either since they run about $700.00 from Nissan! Is your pump located in the fuel tank too? Hope that helps. Edited October 15, 2011 by krmiller07 Link to comment Share on other sites More sharing options...
adamzan Posted October 15, 2011 Share Posted October 15, 2011 Since it only does it when it gets warm (according to your post) I would look into a defective new o2 sensor (unplug it and see if the truck runs better) or the coolant temperature sensor, it is known to cause these kinds of problems. Link to comment Share on other sites More sharing options...
Kingman Posted October 15, 2011 Share Posted October 15, 2011 That won't make his fuel pressure drop to 20PSI under load. Unplug the pressure regulator for a few, see if it makes any difference. That'll force the pump to run at full pressure. If it maintains more than 40PSI while driving your regulator is probably defective. Or if it doesn't make a difference it might be time to pull the pump. Link to comment Share on other sites More sharing options...
TugboatTony Posted October 16, 2011 Author Share Posted October 16, 2011 I know it sounds stupid, but is the fuel filter on the 'right'way? I'd also check the condition of the fuel lines and make sure none of them are collapsing, kinked or obstructed. It is possible you have a bad fuel pump. This happened to me a few years ago. I went through 6 'good fuel pumps' before changing brands, and settled with a Bosch fuel pump before the same problem you described was corrected. My truck would idle for as long as I wanted, however under 'load' or driving it would stall out and quit at exactly the same place while driving up the road. It was running the lines dry under load, but idleing it was fine.Stay away from the Airtex and AC Delco replacement pumps. I wouldn't recommend a Nissan pump either since they run about $700.00 from Nissan! Is your pump located in the fuel tank too? Hope that helps. That sounds a lot like whats happening to me, it seems to stall out around the same place heading to and from work, I'm going to drive to work with the pressure tester zap strapped to my wiper and watch it on my way to work tonite and see what happens. Thanx for the input! Link to comment Share on other sites More sharing options...
TugboatTony Posted October 16, 2011 Author Share Posted October 16, 2011 Since it only does it when it gets warm (according to your post) I would look into a defective new o2 sensor (unplug it and see if the truck runs better) or the coolant temperature sensor, it is known to cause these kinds of problems. I haven't checked my coolant temp sensor as it seems to be working. On the guage the needle is maybe a quarter inch above the 'c' line, is that the normal needle position? and would the coolant temp sensor cause it to bog down as hard as it is? Link to comment Share on other sites More sharing options...
TugboatTony Posted October 16, 2011 Author Share Posted October 16, 2011 That won't make his fuel pressure drop to 20PSI under load. Unplug the pressure regulator for a few, see if it makes any difference. That'll force the pump to run at full pressure. If it maintains more than 40PSI while driving your regulator is probably defective. Or if it doesn't make a difference it might be time to pull the pump. awesome, i'll check it with the vacuum hose off. thanx for the tip!! Link to comment Share on other sites More sharing options...
Precise1 Posted October 16, 2011 Share Posted October 16, 2011 Since it only does it when it gets warm (according to your post) I would look into a defective new o2 sensor (unplug it and see if the truck runs better) or the coolant temperature sensor, it is known to cause these kinds of problems. I haven't checked my coolant temp sensor as it seems to be working. On the guage the needle is maybe a quarter inch above the 'c' line, is that the normal needle position? and would the coolant temp sensor cause it to bog down as hard as it is? There are two temp sensors right next to one another. One to the temp gauge, one to the ECU. The ECU one is what Adam is talking aboot. The FSM is available for download, pinned in the Garage section for the details and it is worth doing... B Link to comment Share on other sites More sharing options...
Tungsten Posted October 16, 2011 Share Posted October 16, 2011 I haven't checked my coolant temp sensor as it seems to be working. On the guage the needle is maybe a quarter inch above the 'c' line, is that the normal needle position? and would the coolant temp sensor cause it to bog down as hard as it is? It should be somewhere between 1/2 and 1/4 way on the gauge. That would be considered normal. Link to comment Share on other sites More sharing options...
TugboatTony Posted October 16, 2011 Author Share Posted October 16, 2011 There are two temp sensors right next to one another. One to the temp gauge, one to the ECU. The ECU one is what Adam is talking aboot. The FSM is available for download, pinned in the Garage section for the details and it is worth doing... B Yeah i fihured out whichj one it was by unplugging it and checking the guage. I'm gonna download the FSM tomorrow. Thanx again for your help Link to comment Share on other sites More sharing options...
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