Idles great, makes a noise and feels like a backfire in drive

OBUCK50

MEMBER
1990 FORD BRONCO
5.8L
V8
4WD
AUTOMATIC
200,000 MILES

I was driving my vehicle the other day and when I was heading to my destination I would notice a feel like a backfire. As I was leaving to head back home it got progressively worse and the backfire became more violent, to the point where I'm not certain it's a backfire with how much it affects my car. I put seafoam in the intake to see if that would help and it didn't. I then replaced the motor mounts thinking that would fix the problem and it didn't. I'm now thinking MAP sensor. Like I said in the title it idles great, but if I put it in drive or reverse it backfires and shakes bad.

3 Replies

JACOBANDNICKOLAS

MECHANIC
108,355 POSTS

Hi,

It could be a few things. Most times, a backfire is caused by excessive fuel to the engine. Take a look through this link:

https://www.2carpros.com/articles/engine-backfires-while-running

Here is what I recommend. This vehicle has an OBD1 computer system. You can retrieve diagnostic trouble codes without a scanner. That is what I need you to do. Here is a link that shows how it is done. Do this and let me know what codes are found.

https://www.2carpros.com/articles/ford-lincoln-mercury-obd1-1995-and-earlier-diagnostic-trouble-code-definition-and-retrieval

Let me know what you find.

Take care,

Joe

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Friday, April 30th, 2021 AT 8:24 PM

OBUCK50

MEMBER
2 POSTS

So the codes that came up are 33, 59, 62, and 67.

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Sunday, May 2nd, 2021 AT 3:03 PM

JACOBANDNICKOLAS

MECHANIC
108,355 POSTS

Hi,

Three of the codes are related to the transmission, so I don't think they are causing the backfire. However, code 33 is a different story.

Code 33 is related to the exhaust gas recirculation (EGR) system and that can be the cause of the issues.

If you look at pic 1 below, it provides the directions for testing. Let me know if that is something you feel comfortable doing.

As far as location, the EGR is mounted on the top right of the intake manifold. See pic 2

The one in the picture has an electrical connector. Yours can have the same or a vacuum hose running to it. If it is a vacuum, check to make sure the hose is attached and not damaged.

If it is, then remove the EGR and inspect it to see if there is carbon or dirt blocking an air flow or preventing the pintle on the valve from moving.

Let me know what you find.

Joe

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