When accelerating it bogs down and backfires and hardly has enough power to get to the next gear

Tiny
NALLEN@RBISOLAR.COM
  • MEMBER
  • 1995 FORD F-450
  • 7.5L
  • V8
  • 2WD
  • AUTOMATIC
  • 99,000 MILES
I have the truck listed above Super Duty dump truck. It starts up great, idles great, but struggles really bad to accelerate, but only sometimes (most of the time actually). Sometimes, I can take off in second gear and it helps. Often times, if I'm driving it for long enough, 15-20+ minutes, it runs and accelerates normal.

I have replaced the MAF sensor, idle air control, throttle positioning sensor, distributor cap, plugs, wires, fuel filter, oil change, practically all new hoses, EGR is currently capped off, waiting on the EGR delete kit to come in the mail.

Used the OBD1 scanner, and 3 items came up; code 32, 33, and 76. 32 and 33 are related to the EGR, which should go away after the delete kit is on. 76 is the vane airflow sensor, which I'm assuming is the same as the MAF, but this is brand new.

I'm thinking it could be the ECU/PCM. I feel like we've replaced everything that would effect the acceleration and cause serious power loss and bogging. Any thoughts would be greatly appreciated!
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Tuesday, November 26th, 2019 AT 5:42 AM

6 Replies

Tiny
JONNYB1963
  • EXPERT
Good morning,

The one that sticks out to me as the most plausible is the 76 Code.

I see that you replaced the VAF (MAF) already without any improvement. While you are waiting for the EGR delete kit to arrive, I would be be looking at the wiring to the VAF. Look for broken wires and corroded terminals. IM not sure where you live, but here in Michigan, with the salty winters, they can get bad over time.

Regards
Jon
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Tuesday, November 26th, 2019 AT 7:48 AM
Tiny
NALLEN@RBISOLAR.COM
  • MEMBER
Jon, thanks for the reply. The connections appear to be okay. I'm located in the Cincinnati area, so plenty of salty winters as well. In addition, we used some kemtool to clean out the MAF hose to ensure it wasn't clogged.

Could the ECU be the issue and not come up on the scan tool?
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Tuesday, November 26th, 2019 AT 7:54 AM
Tiny
JONNYB1963
  • EXPERT
It is possible but it would be rare.

The next thing would be to trace the wiring between the VAF and the ECU although at present I am unable to supply you with a schematic. I'll try to fix this soon and if I can I will upload the schematic.

Jon
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Tuesday, November 26th, 2019 AT 7:59 AM
Tiny
JONNYB1963
  • EXPERT
Okay, I have the schematics now.

You will need a multi-meter to perform this test:

Step 1.
Disconnect the MAF (VAF) sensor connector.
With the Key on, Measure the voltage between pin "B" and ground. (Should be 5 volts) If the voltage is correct, Proceed to Step 5

Step 2.
If it is less, than 5 volts, disconnect the PCM connector, then change to the Ohms setting on your meter, and measure the resistance between that same pin (B) and ground. (It should be higher that 10K (10,000 ohms) The higher the better. If the resistance is good proceed to step 3. If you have resistance lower than 10,000 Ohms then you have a short circuit to ground somewhere in the wire.

Step 3.
If the voltage is higher, then you have a short to power (battery) somewhere and you will need to find that short. Proceed to step 5

Step 4.
Check for continuity between the MAF sensor connector pin "B" to pin 90 on the PCM connector. It should read less than 3 ohms. If it reads higher resistance then repair the circuit. Look for broken or frayed wires, corrosion etc.

Step 5.
Check continuity between MAF connector pin "A" to pin 91 on the ECU connector. It should read less than 3 ohms. If it reads higher resistance then repair the circuit. Again, look for broken or frayed wires, corrosion etc. If it reads 3 ohms or less make one more check. Read the resistance between Pin "A" to ground. That reading should be 10K ohms or greater. If not, you have a short circuit on that wire.

Step 6.
Check continuity between MAF connector pin "C" to pin 58 on the ECU connector. It should read less than 3 ohms. If it reads higher resistance then repair the circuit. Again, look for broken or frayed wires, corrosion etc. If it reads 3 ohms or less make one more check. Read the resistance between Pin "C" to ground. That reading should be 10K ohms or greater. If not, you have a short circuit on that wire.

Here are the schematics to help:

Jon
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Tuesday, November 26th, 2019 AT 1:04 PM
Tiny
NALLEN@RBISOLAR.COM
  • MEMBER
I'll give it a shot and update you when I do! I really appreciate the help.
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Tuesday, November 26th, 2019 AT 1:23 PM
Tiny
JONNYB1963
  • EXPERT
Woops I edited the last entry I made. In step 6 I accidentally wrote pin "a" when I meant Pin "c" it is fixed now.
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Tuesday, November 26th, 2019 AT 1:47 PM

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