Bad fuel pump?

mr2mk1hero
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Bad fuel pump?

Postby mr2mk1hero » Mon Mar 20, 2017 1:33 am

Car was stalling occassionally a month or so ago. I found a bad ground. The bolt where the battery cables ground on the chassis was not completely bolted down. So I bolted it down and added another ground. That was a couple of days ago and the tempreature was till pretty cold. Car did not stall anymore back then. I thought problem solved.

Spring is here now and temps are warmish.....car stalls almost everytime I am coming to a stop now. Also wants to die when I am standing still and I blip the throttle a bit. The rpms drop all the way to 400 or so and the engine wants to die. Sometimes it dies, sometimes it just shakes and comes back to 900. If I blip the throttle more, like rev it to 4000 or more it will stall every time. It will never stall while driving.

Its also sometimes hard to start when hot, sometimes it starts right away easily when hot.

While driving it feels like there's no power at high rpms, beyond 5500 rpm it goes through rpms more slowly and seems to be just making a lot of noise rather than power. I have mild cams that should be making power to 7000. I tried different settings with adjustable cam pulleys but weirdly enough they dont make a lot of difference. 110 vs 108 lsa feels almost the same.

Rebuilt engine, timing is spot on 10btdc, new distributor cap, new plugs gapped properly, new plug wires, almost everything is new. I measured the resistances at my afm a month ago and it was within spec.

I am thinking about taking it somewhere to measure the fuel pressure since I don't have that tool. I am thinking this is the fuel pump? Any other ideas that I might be able to check myself? Thank you
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s24a
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Re: Bad fuel pump?

Postby s24a » Mon Mar 20, 2017 5:43 am

If the engine ran better overall in cold weather, and also runs OK when cold in the "warmish" temperatures, might not be fuel pump as cold engines/cold weather typically need MORE fuel so the pump would act up then.

Have you looked at the ISC valve to make sure that it is functioning correctly and not sticking?
If sticking, it can generally be cleaned with brake cleaner (you will have to remove off car.

Another possibility somewhat related is throttle icing if your throttle body has the coolant warming circuit.
As you did not mention the temperature, if it is in the high 30s (F) to mid 40s (F) and humid, that can be the zone for icing.

Hank
"When the going gets, wierd, the Wierd turn Pro" -- Hunter S. Thompson

davew7
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Re: Bad fuel pump?

Postby davew7 » Mon Mar 20, 2017 6:02 am

Stalling: check at the throttle for a defective diaphragm at the linkage, which allows the throttle to close to quickly Vs slowing the movement during last dit of travel. Could also be the wax-stat problem.
Fuel problem could be the filter. Break the line and insert the fuel line into a bottle and jump the fuel pump wiring to verify flow. Any low pressure gage will work. Just install a barb fitting and attach to the fuel line. You could have an injector(s) that needs cleaning.
For the higher RPM problem I would verify the T-VIS system is operating. [Ck linkage movement, you could try locking the linkage for a test run]
I have my mild intake cam set at 105* which improved mid-range.
Dave W

mr2mk1hero
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Re: Bad fuel pump?

Postby mr2mk1hero » Mon Mar 20, 2017 6:38 am

Thanks for the responses guys!

s24a wrote:If the engine ran better overall in cold weather, and also runs OK when cold in the "warmish" temperatures, might not be fuel pump as cold engines/cold weather typically need MORE fuel so the pump would act up then.

Have you looked at the ISC valve to make sure that it is functioning correctly and not sticking?
If sticking, it can generally be cleaned with brake cleaner (you will have to remove off car.

Another possibility somewhat related is throttle icing if your throttle body has the coolant warming circuit.
As you did not mention the temperature, if it is in the high 30s (F) to mid 40s (F) and humid, that can be the zone for icing.

Hank


ISC valve is dead. Car used to have high idle and would die once it warmed up. I blocked it off and car now runs at 900-1000 rpm completely stable.

Cold temperetarues were 20, 30-40 etc. Warm now is 50 -60

davew7 wrote:Stalling: check at the throttle for a defective diaphragm at the linkage, which allows the throttle to close to quickly Vs slowing the movement during last dit of travel. Could also be the wax-stat problem.
Fuel problem could be the filter. Break the line and insert the fuel line into a bottle and jump the fuel pump wiring to verify flow. Any low pressure gage will work. Just install a barb fitting and attach to the fuel line. You could have an injector(s) that needs cleaning.
For the higher RPM problem I would verify the T-VIS system is operating. [Ck linkage movement, you could try locking the linkage for a test run]
I have my mild intake cam set at 105* which improved mid-range.
Dave W


Went to a mechanic he did not want to deal with it but told me the very same thing about the throttle body plate being closed too soon. He also says most likely its not the fuel pump. How do I check if that diaphragm that slows the plate down is good or not?
Wax-stat is blocked-off.

Fuel filter is brand new. Injectors have been cleaned, rebuilt and tested.

My mid-range feels good. The best way to describe the high rpm problem is that the engine is difficult to rev out. It takes forever to get from 6000 to 7000 rpm.
Check out my blog: http://www.driving4answers.com/
Lots of photos, info, experiences and fun random stuff from a fellow die-hard AW11 enthusiast. Great for AW11 newbies with no mechanical or DIY experience - I am one so I speak your language

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mr2mk1hero
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Joined: Mon Jan 26, 2015 2:40 am

Re: Bad fuel pump?

Postby mr2mk1hero » Wed Mar 22, 2017 12:22 pm

So I went to the garage today to take a better look.

T-vis is not working. Reved the car up beyong 4000, there is zero movement. All my vacuum lines are connected properly.

The little diapraghm on the throttle body is also not moving and not making contact with the little bolt. Its dead? I need a new throttle body right? Can't replace just this thing?

Also my battery ground (on the strut tower next to the battery) and my ECU ground on the intake manifold might be bad. When I put one probe on the battery negative and the other on the ground bolts. Sometimes there is continuity, sometimes there isn't, mostly not tho. I have to like push hard or scratch the bolts with the probe to get continuity. I remembered I painted the exterior of the t-vis....could this have effed up my ground? I was careful not to paint any of the surfaces where the gaskets go. Should I make an alternative ground? Could bad ECU ground be causing the t-vis not work. Also engine is kinda hard to rev beyond 5000 rpm while at idle.
Check out my blog: http://www.driving4answers.com/
Lots of photos, info, experiences and fun random stuff from a fellow die-hard AW11 enthusiast. Great for AW11 newbies with no mechanical or DIY experience - I am one so I speak your language

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