Engine 89 5.0 Backfiring/Missing Under WOT

[deserthoundLX]

Was hoping i could get some input on where to start diagnosing a backfiring/popping/missing thats occurring under WOT in my 89 302. Recently replaced the fuel pump, lines and tank, as well as o2 sensors and idle control valve. The only codes i have are for the EGR valve which is capped because im unsure if its leaking or not and TAD/TAB which are deleted from PO. Any insight would be appreciated. thanks in advance

 

[Noobz347]

Initial thoughts:

Throttle Position Sensor
Inconsistent Spark

Is this a boosted combo?

Check voltage to the coil. If it looks normal, rig up a voltage tester that you can reference while revving or driving. Look for a voltage drop at the top where the breakup occurs.

Check your plug gap.

Do a full sweep test of the TPS and just ensure it is smooth all the way through the range of motion.


The other thought is that you're running lean. Check fuel pressure at the rail. Maybe even install a permanent fuel press gauge at some point. Do you know exactly what the pump is that you installed? Walbro? Some other knock-off brand like Antec or Entex (Chinese BS)? Is it an 88L replacement pump or something else?

 

[General karthief]

I would start by checking condition of the cap, rotor, plugs and wires then monitor fuel pressure particularly in higher RPMs where the problem is.
Is the car stock?
And what Noobz said ^^^^^

 

[AeroCoupe]

I had some misfire issues at high rpm a long time ago and it ended up being the stock distributor bushings were wore out causing the rotor to move around. This was long enough ago that I was able to get a very low mile Ford distributor and that solved the issues I was having.

I did not have backfiring and over the years if a car is falling out face / stumbling / back firing at WOT it’s usually a fuel related issue. You need to righ up a pressure gauge so you can monitor the pressure. If it stays steady the bump it up a few psi and see if that helps.

My car is tuned at 49 psi with the vacuum unhooked and if you bump it down to 39 psi it will fall flat on its face.

Verify pressure and spark and make sure you have no vacuum leaks.

 

[deserthoundLX]

Initial thoughts:

Throttle Position Sensor
Inconsistent Spark

Is this a boosted combo?

Check voltage to the coil. If it looks normal, rig up a voltage tester that you can reference while revving or driving. Look for a voltage drop at the top where the breakup occurs.

Check your plug gap.

Do a full sweep test of the TPS and just ensure it is smooth all the way through the range of motion.


The other thought is that you're running lean. Check fuel pressure at the rail. Maybe even install a permanent fuel press gauge at some point. Do you know exactly what the pump is that you installed? Walbro? Some other knock-off brand like Antec or Entex (Chinese BS)? Is it an 88L replacement pump or something else?

Thank you for your time and help for starters. Not boosted. Ive checked TPS voltage and it appears to be in range (set to .98v) and sweep through the range properly when the TB is actuated. I do get 36-38 Psi at idle with vacuum line attached and 39-40 without. The new pump is a Walbro 155 LPH. I do have a gauge pillar for the fuel pressure as well. On running lean, im almost positive i have a vacuum leak but i cant for the life of me locate it. ive tried smoke testing and the only place smoke comes from is the holes on the EGR valve, which is also new and was replaced recently to fix a code 33.

 

[deserthoundLX]

I had some misfire issues at high rpm a long time ago and it ended up being the stock distributor bushings were wore out causing the rotor to move around. This was long enough ago that I was able to get a very low mile Ford distributor and that solved the issues I was having.

I did not have backfiring and over the years if a car is falling out face / stumbling / back firing at WOT it’s usually a fuel related issue. You need to righ up a pressure gauge so you can monitor the pressure. If it stays steady the bump it up a few psi and see if that helps.

My car is tuned at 49 psi with the vacuum unhooked and if you bump it down to 39 psi it will fall flat on its face.

Verify pressure and spark and make sure you have no vacuum leaks.

interesting. thank you for the insight ill give that a shot and take a look.

 

[deserthoundLX]

I would start by checking condition of the cap, rotor, plugs and wires then monitor fuel pressure particularly in higher RPMs where the problem is.
Is the car stock?
And what Noobz said ^^^^^

Sorry i shouldve included in the OP. Cap, rotor, plugs and wires are all new as part of a tune up when the car was pulled out the garage after a few years.

 

[limp]

35 year old ECU,,, Have you had it checked? or taken apart to look for corrosion or puffy caps?

 

[deserthoundLX]

35 year old ECU,,, Have you had it checked? or taken apart to look for corrosion or puffy caps?

i have not. ill have to give that a check and put some eyes on it. thank you

 

[91 Black Hole]

I had similar problem with my 91. Tried everything suggested here which helped but problem did not get resolved until until I replaced TFI on side of distributor. Lots of bad reviews on motorcraft units so I bought MSD one. It was also the only one I could find that came with the required heat sink film. Hope this helps, mine runs great.

 

[AeroCoupe]

See post #3 with regards to testing TFI modules.

Engine - 1992 5.0 Died while running, crank no start, Tach Jumping

Wondering if someone can help. My 1992 5.0 5 speed died while on a drive home the other night. It cranks but wont start. Couple things to note- (not the battery) - OBD1 is showing code 95, 11, 10. - There is fuel at the valve that sprays out when pressed. - Tried checking for spark, didn't get...

stangnet.com

 

[deserthoundLX]

I had similar problem with my 91. Tried everything suggested here which helped but problem did not get resolved until until I replaced TFI on side of distributor. Lots of bad reviews on motorcraft units so I bought MSD one. It was also the only one I could find that came with the required heat sink film. Hope this helps, mine runs great.

appreciate the info. ill keep that in mind and give it a shot.

 

[deserthoundLX]

See post #3 with regards to testing TFI modules.

Engine - 1992 5.0 Died while running, crank no start, Tach Jumping

Wondering if someone can help. My 1992 5.0 5 speed died while on a drive home the other night. It cranks but wont start. Couple things to note- (not the battery) - OBD1 is showing code 95, 11, 10. - There is fuel at the valve that sprays out when pressed. - Tried checking for spark, didn't get...

stangnet.com

Appreciate your help and time. will check this out now.

 

[deserthoundLX]

Quick Bump/Update.

Replaced the fuel pressure regulator and the problem improved but only slightly. Today i replaced the tfi module and it now drives maybe 75% better with only the occasional power loss/popping/backfiring. Still only getting 10 in/lb vacuum at idle at around 850 rpm. No smoke besides the holes on the egr valve body. maybe the lower intake?

 

[Blown88GT]

Quick Bump/Update.

Replaced the fuel pressure regulator and the problem improved but only slightly. Today i replaced the tfi module and it now drives maybe 75% better with only the occasional power loss/popping/backfiring. Still only getting 10 in/lb vacuum at idle at around 850 rpm. No smoke besides the holes on the egr valve body. maybe the lower intake?

Should be 18-20 in-Hg. You have a big vacuum leak.

 

[deserthoundLX]

Should be 18-20 in-Hg. You have a big vacuum leak.

thanks, i thought so but its been driving me crazy trying to locate it. im thinking its in the lower intake or somewhere smoke wont be visible.

 

[AeroCoupe]

Run the engine and spray (in moderation) carburetor cleaner around the lower intake and see if the rpms pick up. If so you have a leak.