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Bad fuel pump?

2K views 24 replies 4 participants last post by  evintho 
#1 ·
In addition to my bad ECU, I think the fuel pump is going out. I bought the car as a 100k vehicle but in reality it might be 200k. I use to turn the key and it would fire right up and fast idle at 1100 rpm then drop after 30 seconds to 800-900.
Now, I turn the key, it fires up then dies. I have to feather the throttle in the 1800-2000 range to keep it running. After a couple of minutes it settles in and runs and idles fine. Also the FP makes an inordinate amount of noise!
I replaced the FP relay about a year ago. I've never changed the fuel filter (figure I'll do that when I change the FP).

I have a Walbro that was in Thunderstang with about 4k miles on it however, it's been sitting on a shelf for the last 5 years. I was contemplating installing that. Are there any seals/O-rings inside the pump body that may have dried out/shrank/etc? It's not too hard to drop the tank. I figure if I can get away with running that one I will have saved $80, if not, I'll drop the tank again and buy/install a new one. Let's hear your thoughts!
 
#2 ·
Maybe check the fuel pressure? I guess you could check key on engine off and then again when it finally idles.
I had a fuel pump go out in a cougar that I had. The motor shut off and wouldn’t start. It didn’t “get weak” and then die. It was instant death. A louder than once was pump would make one think ones on its way out though. If it is the pump surely you’ll have a no start condition soon.
You don’t think the stalling etc is related to the bad ecu?
 
#3 ·
Yeah, it could very well be the ECU. With the loud FP, I figure it's probably on it's way out so I'll just replace it and repair the ECU at the same time.
 
#4 ·
I'd put a pressure gauge on the fuel rail and turn the key forward see if pressure ramps up and if it holds then see if it holds while cranking... If not , figure out where (maybe at fuel pump relay output ) if the relay loses power , I'd blame the ecu or that combination-module that also controls fan speed..... If you have one... Not sure if we're talking fox or sn95.
 
#5 ·
I don't think it'd be a relay really since it starts. If a relay was bad and it wasn't getting power I'm pretty sure it'd just crank and not start. I think his is a fox so no CCRM, but the CCRM is just a box with a bunch of relays in it. So if anyone with a '94/'95 has an intermittent problem the CCRM is probably not to blame.
 
#6 ·
Sometimes when the pump is getting ready to go out,the pump check valve will cause fuel pressure to bleeddown as soon as you turn the key off.So if you turn the key on and take a reading,then turn the key off,wait 60 seconds then take another reading,a loss of more than 5psi in that 60 second period means the check valve is bad or the fpr is bad.If pressure bleeddown,as mentioned, does occur,you can verify its the pump that's at fault by pinching a soft section of the fuel return line closed,then do the same pressure test and if pressure still continues to bleeddown,that verifies the pump is bad. Keep in mind there are other things that can go out in the pump also besides the check valve.So even if the bleeddown test passes, the pump could still be bad.Make sure the iac valve is working properly too as its one of the primary causes of immediate stalling upon startup.The iac is commanded fully open by the ecu during cold starts to bypass air around the throttle blade so the engine will idle.Internal engine parts create more friction when cold.
 
#7 ·
Make sure the iac valve is working properly too as its one of the primary causes of immediate stalling upon startup.The iac is commanded fully open by the ecu during cold starts to bypass air around the throttle blade so the engine will idle.Internal engine parts create more friction when cold.
That's a good idea and makes perfect sense! Is there a testing procedure for the IAC?
 
#12 ·
That's a good idea and makes perfect sense! Is there a testing procedure for the IAC?

With the engine at operating temp,when you disconnect the iac harness,the engine should stall or the idle should drop slightly, depending on how far inward the throttle body idle adjustment screw is set.If the iac is just dirty,& not defective,idle will normally bounce around surging up and down. However a defective iac can also cause this,if cleaning it doesn't help.
Mechanical idle is the rpm value you set with the tb screw,with the iac harness disconnected.Computer controlled idle is the idle rpm value the ecu sets,with the iac harness reconnected.Mechanical idle should be set between 550-650rpm then the ecu will control idle above that value.672rpm is the target value the ecu looks for.If mechanical idle is set too high,the ecu might not be able to lower idle to the ecu target.

There are several tests for the iac/wiring. With the key on,the red iac wire should read 10.5-12v.Use the engine block as the ground for the multimeter.With the engine running, the white/lt blue iac wire should toggle between 12-.5v,with the meter leads between the red and white/lt blue wire terminals.If there is a short to ground in the white/lt blue wire or the iac body to internal wiring,the meter will usually not read above 1v during the w/lt blue wire test.With the harness disconnected,meter set to ohms, touch each iac terminal with a multimeter lead.The meter should read between 7-13 ohms one way then when the meter leads are reversed on the terminals,the meter should read OL or open loop,since the iac has a diode in it.This is for 89-93 & all remanufactured iac's.86-88 models had a diode inline with the iac harness instead, while 89-93 models (& all remanufactured iac's now sold) had a diode in the iac itself.If its a 86-88 iac you're testing,both test directions listed above with the meter, should read 7-13ohms.Now touch one meter lead to the iac body and touch the other lead to one iac terminal then move it to the other iac terminal.The meter should read OL or a very high ohms reading for both terminal tests.
Evin, sorry about the thread jacking.
I tested my IAC today with a noid light like the guy did in the video. It lit up when I turned the key on, but it did not stay illuminated like the one in the video. It just came on and went back off. I probed the red wire at the plug and it read 12v (12.5 I think it was). It read a constant 12, it wasn’t “on and off” like the noid light was. I reconnected the IAC and I had someone turn the key on while I listened to the IAC body with a mech’s stethoscope and I heard a click click. Would y’all diagnose this as a working IAC or is that still TBD?
 
#11 ·
Thanks, you guys! I installed my used Walbro FP last week and after installation I still had the starting and dying issue until it warmed up a bit. Took the car for a drive and got about 20 miles before the FP started singing like a canary and would barely run! Called AAA and towed it home. My new Walbro just came in the mail today so I'll be installing it this weekend. After that I'll give the IAC a test and clean. If that's not it I'll have to go for the remanned ECU.

A little update on the ECU. I Pulled it and took the cover off. All 3 capacitors looked good and weren't leaking. I then took it into the local electronics repair guy and he looked it over real good and said he couldn't see anything obviously wrong with it. I called Autozone and it turns out their $158 remanned ECU is now unavailable however, I can send in my ECU and their supplier will rebuild it for $235 with a 5 day turnaround time. May have to go that route.
 
#15 ·
Good info!! The new FP is going in today. I'll test the IAC after that.
90lxwhite:
No worries on the thread hijack! This forum is all about information sharing. I just wish the mods would figure out the Imgur issue.
 
#16 ·
OK, new FP is in and works good however, the car still does the same thing at cold start. Fires up, then dies and barely runs until it gets up to temperature. Once warmed up, it runs fine. Took it on a 90 mile cruise yesterday!
So.....I tested the IAC. First thing I did, once it was warmed up, is disconnect the IAC. The motor didn't drop any RPMs at all!
Reconnected the harness and probed the red wire with key on. I got 12.5v.
Motor running. Red meter probe to red wire, black meter probe to wht/lt blue wire. I got 4.35v - 4.65v.
Removed the IAC entirely and ohmed it's terminals. I got .012 ohms both ways.
While the IAC was off I soaked it with Brakeclean and even scubbed a little inside the ports. Reinstalled it and it does the same thing!
Please tell me it's just a bad IAC!
 
#17 · (Edited)
Stack a penny & a nickel and place them between the stop screw and the "arm" on the TB so it holds the TB open a little. If it idles better I think you're on the right track thinking iac.
*edit*
I think doing so kinda takes the IAC out of the equation. Will yours start with the IAC unplugged? Mine would not, but I believe it’s supposed to be able to.
 

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#19 ·
OK, my bad! Firstly, the '89 went to that big Mustang graveyard in the sky a couple years back when some idiot rearended me at 40 mph and totalled the car. The current project is a '93 LX 5.0 ragtop...................



And, my electrical skills are abysmal at best so please bear with me. I set my meter on the lowest setting, I think, which was 2k when I ohmed out the IAC and got the .012 readings.

 
#20 ·
Oh ok.Youre still fine as far as the testing goes that I listed in my previous post.If you would have had a 86-88 model instead,your test results would have been different than the ones you got for a 89-95 model.IOW-
86-88 should have the same ohms value regardless of which way you connect the leads.89-95 should have totally different values when you test the terminals one way then reverse the leads and test the terminals the other way.
 
#22 · (Edited)
It sure sounds like it.If its a oem iac from a 89-93 model or a remanufactured iac & its reading the same ohms value with the test leads connected in both directions,its defective.Only the oem iac's from the 86-88 models should read the same (7-13) ohms value in both test directions.Reasoning???
86-88 models have a diode wired into the iac "HARNESS" while 89-93 models have a diode built-in to the iac "VALVE" instead.(Reman iac's have the built-in diode too) If you're not the original owner & the previous owner installed a 86-88 oem iac,that could also make it read the same value both ways too.However if the correct iac is currently being used and your tests showed .012 both ways,the iac is definitely bad.....

**NOTE**
Is the 2k setting the lowest ohms value your meter has or does it also have a 200 or 20 ohms setting too?? If it has a lower setting than 2k,turn the knob to that setting and retest your iac in both directions.You want the meter to be set on the ohms value that is slightly higher than the value you expect to see on the component under test.
Example: if the component is supposed to have a value of 100 ohms when tested,you'd want to set your meter on the 200 ohms setting (if your meter has that setting).Since the value youre expecting to see on your iac is between 7-13 ohms,you'd want to set the knob on the 20 ohms setting (if your meter has that setting) since thats slightly above the value of 7-14 ohms you're looking for.My meter starts at 200.

Another test for the iac is to let the engine idle at operating temp,turn the ac on max & listen to how the idle reacts.When the ac is turned on,the ecu commands more duty cycle to the iac to compensate for the additional load of the compressor,so if the idle drops & it doesn't immediately recover, the iac is indeed suspect,as long as the iac wiring is ok.
 
#23 ·
As you can see from the pic, I have 200k, 20k and 2k followed by 200 with the 'beep' symbol. I tested it on the 2k graduation and got the .012. I tried the 200 also and got a constant 'beep' and I think the reading was 7. And yes, I tested both ways, red lead on one terminal and black lead on the other then, I swapped the leads and got the same readings.

I noticed this morning when I started it up, the problem seems to have gone away! It fires and runs about 1100 rpm then drops after a few seconds to about 800. I guess the cleaning helped it. I do notice however, that once it gets to 800, there's a surging idle. Probably 100 rpm in each direction. I'll bet that has something to do with that old, dirty IAC! Cheapest Motorcraft I've found seems to be RockAuto @ $61 shipped. I think I'll just bite the bullet and go for a new one. wbrockstar, you are a wealth of knowledge! Thank you very much! Thanks to others who chimed in, also!
 
#24 · (Edited)
You can try doing a base idle reset now or wait until you get/install the new iac. Anytime the base idle is set above 650rpm,w/ iac harness disconnected, surging issues can begin.This may/may not be your issue.The following copied/pasted instructions should help.


Summarized/Corrected Base Idle Reset version
1) Clean TB with carb cleaner and nylon brush (if needed) Engine off, fully open TB blade and spray/brush TB until all gunk and oil residue is cleaned.


2) Allow to dry, or close TB blade and start engine until it clears all carb cleaner fumes/liquid.

3) Remove the spout plug,just to make sure the ecu doesn't have any input on timing during the reset procedure.Let engine idle...if it doesn't, increase idle speed via TB stop screw until engine stays idling on its own.

4) Disconnect IAC valve, if engine dies repeat 3 with IAC disconnected.

5) Set idle speed to the lowest setting possible between 550-700 rpms with IAC disconnected. It is key to use the lowest possible to prevent idle surge, rolling, etc once the IAC is connected as follows.

6) Turn engine off, and reconnect IAC

7) With Ign On Eng Off, check TPS voltage output....if it's between .7vdc - 1.0vdc, it's OK. This voltage check should be done between the Green and Black wires at the TPS side connector as shown in the pic below....(-) terminal of the DVOM on the Black wire and (+) terminal on the Green wire.

8) Disconnect battery (-) for 3-5 minutes.

9) Reconnect battery, start engine, allow it to idle for 2-4 minutes to confirm setup,

10) If idle speed falls too low or stalls, increase idle speed via the TB set screw a little at a time.

11) Turn engine off for 20 seconds, re-start engine and repeat 9 - 11 if required.

12) Reconfirm TPS output is within .70 - 1.0vdc range.......you're done!...

..no need to reset ECM KAM (reset computer) b/c the TPS minimum value used for idle control, is automatically reset by the EEC-IV every time the ign is cycled on-off for 20 seconds-on, and as explained in the next post

13) Allow a 10-20 minute "relearning" period under normal driving conditions (drive cycle).....now you're done.
 
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