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1991 Bronco XLT, 5.0L, automatic, 3.55 gears
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155 Posts
Discussion Starter · #1 ·
Today on the way to work the bronco died sitting at a light. It wouldn't restart. Cranked well but no fire, felt like it was flooded or air intake was restricted. I took off the inlet duct from the throttle body, it fired up and drove. I revved it to 4k rpm to see if everything felt smooth and it had 1-2 gunshot sounding backfires from yhe exhaust. Revved it again to 4-5k rpm and 2-3 loud back fires. Can anyone help me understand what could cause this type of backfire? Pulled codes when I got it home and had 327, 328, 332, 556. I had no codes prior to this issue. I know these are egr related. I recently replaced the egr valve and solenoid several months ago and haven't had any issues. Any ideas/suggestions what it could be or where to start?
 

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1986 Eddie Bauer 5.0EFI AOD Full length headers Y pipe into single 3" Magnaflow 3" factory exit
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1,400 Posts
Try pulling the vacuum line off of your egr & capping it, your egr pintle may be gummed up & stuck open, which they won't run at idle with that open, and the egr is supposed to close at WOT, so both of those sort of fit, along withnthe egr codes, that's what I'd look into. Can't say for sure, but I'm saying theres a chance.

When getting my egr operational after decades of it not working, I put the new pintle on & tried hooking vacuum to it, which it wouldn't start. Then I unhooked the vacuum line, & capped it & it started right up? I then reattached the vacuum line & it stalled. Thats when I read into how it works more thoroughly & figured out my egr control solenoid was bad. I replaced that, and it corrected everything. The computer tells the solenoid to open the egr under certian conditions, and that is cruising speed only. It is closed at idle, and WOT, so that is why I suspect either that solenoid is bad and allowing vacuum all the time to the pintle, or the pintle is stuck open by exhaust gunk.
 

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Yo Jah,

DTC 327; "...It's not that the engine problem causes the transmission problem, it's just that engine problems can easily be mistaken for transmission problems. If you have a shudder under load it could be a problem with the converter clutch, or it could be due to a problem with the EGR system causing the engine to misfire under load. If the converter clutch is unlocked and slipping the converter slippage can mask the misfire, and when the converter locks the misfire is noticable because the converter slip is gone. I would definitely take care of the EGR system first since it can cause misfires, and is likely to be much less expensive to repair than a transmission problem..." Page 2
Source: by Baumann Electronic Controls, LLC becontrols.com

DTC 328, 327 or 337 Troubleshooting; Continuous Memory DTC 328 or 327 indicates the EGR valve was closed further than normal or EVP sensor or circuit has failed with an intermittent low voltage sometime during vehicle operation. Continuous Memory DTC 337 indicates the EVP signal to the Powertrain Control Module (PCM) was above the maximum Self-Test limit sometime during vehicle operation. Possible causes: Poor continuity in EVP harness or connectors. Intermittent open or short in EVP sensor or harness. Damaged EVP sensor..." READ MORE
Source: by SigEpBlue (Steve) at FSB

DTC 332, P1407 and P1408 or detonation; "...We have run into many situations where a code for insufficient flow has been set and the system is functioning correctly. Then it is time to check the EGR passages. There is a Ford Technical Service Bulletin (TSB 96-23-4) that addresses this for some vehicles. This TSB includes: 1992-1995 Crown Victoria 1994-1995 Thunderbird 1991-1995 Town Car 1992-1995 Grand Marquis 1994-1995 Cougar The concerns have to do with intermittent MILs; DTCs 332, P1407 and P1408; or detonation. If exercising the EGR valve does not result in a change in rpm, then the passages may be clogged. There are “U” shaped passages (Fig. 6) under the throttle body adapter that get clogged with carbon. Remove the adapter, clean the passages and reinstall with a new gasket. Just because the vehicle you are working on is not listed in the TSB doesn’t mean you may not have a clogging problem. Make sure you check the passages and be sure they are clean. Just a slight restriction can cause a flow code to be set, and you may still have an rpm drop that can mislead you..."
Source: by tomco-inc.com​
DTC 332; "...Continuous Memory DTC 332 indicates the EGR valve did not open with the engine stabilized and the EVR solenoid duty cycle present sometime during vehicle operation. Possible causes: "...Obstructed or cracked hose to EGR valve,Icing, Damaged EGR valve, Damaged EVR solenoid harness..."
Source: by Ford via SigEpBlue (Steve) at FSB


J1 DIAGNOSTIC TROUBLE CODE (DTC) 556:
CHECK FOR VPWR TO FUEL PUMP RELAY

  • DTC 556 indicates a fuel pump primary circuit failure.
    Possible causes:
    • Inertia Fuel Shutoff (IFS) switch not reset or electrically open (if in primary circuit).
    • Open or shorted circuit.
    • Damaged fuel pump relay.
    • Damaged Powertrain Control Module (PCM).
  • Disconnect fuel pump relay.
  • Key on, engine off.
  • Measure voltage between VPWR circuit at the fuel pump relay vehicle harness connector and chassis ground.
Is voltage greater than 10.5 volts?
YesNo
GO to J2.VERIFY integrity of IFS switch. If OK, SERVICE open in VPWR circuit between the EEC power relay and the fuel pump relay. RECONNECT fuel pump relay. RERUN Quick Test.
J2 CHECK FUEL PUMP RELAY
  • Key off.
  • Fuel pump relay disconnected.
  • DVOM on 200 ohm scale.
  • Check fuel pump relay coil resistance:
    • For "ISO" relays, measure resistance between Pins 85 and 86 at the fuel pump relay (pin numbers molded on relay).
    • For other types of relays, measure resistance between VPWR pin and fuel pump circuit pin at the fuel pump relay.
    • Resistance should be between 40 and 85 ohms.
  • DVOM on 10,000 ohm scale.
  • Check fuel pump relay for internal shorts.
    • For "ISO" relays, measure resistance between Pin 85 and both Pins 30 and 87 at the fuel pump relay.
    • For other types of relays, measure resistance between the fuel pump circuit pin and both the power-to-pump and B(+) pins at the fuel pump relay.
    • Both resistances should be greater than 10,000 ohms.
Are all resistance checks OK?




YesNo
GO to J3.REPLACE fuel pump relay. RERUN Quick Test.
J3 CHECK FUEL PUMP CIRCUIT FOR SHORT TO POWER
  • Key off.
  • Fuel pump relay disconnected.
  • Disconnect Powertrain Control Module (PCM). Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.
  • Install breakout box, leave PCM disconnected.
  • Key on, engine off.
  • Measure voltage between Test Pin 22 at the breakout box and battery negative post.
Is voltage less than 1.0 volt?
YesNo
GO to J4.SERVICE short circuit. REMOVE breakout box. RECONNECT all components. ATTEMPT to start vehicle. If vehicle fails to start, REPLACE PCM. RERUN Quick Test.
J4 CHECK FUEL PUMP CIRCUIT FOR SHORT TO GROUND
  • Key off.
  • Breakout box installed, PCM disconnected.
  • Fuel pump relay disconnected.
  • Measure resistance between Test Pin 22 and Test Pins 40 and 60 at the breakout box.
Is resistance greater than 10,000 ohms?
YesNo
GO to J5.SERVICE short circuit. REMOVE breakout box. RECONNECT all components. RERUN Quick Test.
J5 CHECK FUEL PUMP CIRCUIT CONTINUITY
  • Key off.
  • Breakout box installed, PCM disconnected.
  • Fuel pump relay disconnected.
  • Measure resistance between fuel pump circuit at the fuel pump relay vehicle harness connector and Test Pin 22 at the breakout box.
Is resistance less than 5.0 ohms?
YesNo
REPLACE PCM. RECONNECT fuel pump relay. RERUN Quick Test.SERVICE open circuit. REMOVE breakout box. RECONNECT all components. RERUN Quick Test.

 

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1991 Bronco XLT, 5.0L, automatic, 3.55 gears
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155 Posts
Discussion Starter · #5 · (Edited)
It happened again today but this time I noticed no fuel pump prime at key on. Feeling around the plug on the fuel pump I noticed the tabs that hold the plug onto the pump are broken and the plug wasn't making good contact. Pushed it back on, started right up and made it home. Just need to get a new harness to fuel pump connector.
 
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