I hope this is the right forum. OBD-I code question. This truck/engine has 220,000 miles. 4 months ago it would start, idle fine, but then die when the accelerator was depressed. I didn't have time to diagnose the problem or work on it so I let my local mechanic do it. He replaced the MAP sensor and it ran OK for 3 months. Then it again started to hesitate when I accelerated. Now it just dies like it did 4 months ago. Starts and idles OK.

I decided to attempt diagnosis myself this time. I used the KOEO method posted at fordfuelinjection.com to pull the codes by grounding the STI and counting the CEL flashes. I keep getting 33 which is an EGR code. Does this seem right for the symptoms? Any other suggestions?

Penthor

 

Ewww - gonna have-ta defer to the more experienced members here.

Thinking MAP was replaced by MAF much earlier. Wondering about TPS???

Acceleration is a tough beast - not only is the air flow increasing, but the fuel flow needs to follow proportionately.

Where's Sean or Dr. Bowtie when you need them :-)

 

Are you sure it's giving you a 33? On a '95, you should get 3-digit codes, and I'd bet that it's actually 111, 111 (which is system pass). As WDE said, a 95 doesn't have a MAP sensor, but is does have a MAF sensor in the intake plumbing.

111 is good, but it's bad because we're left guessing.

When was the last tune-up (plugs, wires, cap, rotor)?

How is the fuel filter?

Past that, the TPS could be a place to check, or even just cleaning the throttle body and IAC.

 

Thanks for the input aliens. You may be right about the self-test codes, I was unsure about how to interpret the flashes.

The mechanics receipt I have says the MAP sensor was replaced. I have read that the MAP and MAF sensors served a function similar to the old vacuum advances and the symptoms I noted fit that scenario. Since I have no experience with either of these sensors or manually pulling codes, I came here for help. I guess what confuses me most is that after the mechanic did the work this summer the truck ran fine for about 3 months and then began acting up. Can a MAF sensor go bad that fast? Is there a way to test the MAF sensor with a multi-meter?

Again, the engine starts and idles fine. The plugs were changed this summer. Nothing in the distributor has been changed as far as I can remember. I can check and replace any suspect parts there.

I can't say when the wires were replaced last.

The fuel filter was changed many years ago. What’s the easiest way to check if it’s passing the right volume/pressure?

I’ve had experience with dirty IAC valves and throttle bodies; these symptoms didn’t match up with those items from my previous experience with another vehicle. However, cleaning those will not be that difficult.

I’ll see about locating the TPS and testing it. Any advice along that line?

 

This link has some good TPS info:

http://autorepair.about.com/od/diano...a042603a05.htm

It's mounted on the bottom of your throttle body.

The only thing I can think of regarding this situation going away, then coming back 3 months later, is that the mechanic may have cleaned the MAF sensor (not replaced it?)

I really think it's fuel related... you know? getting enough pressure to idle, but when you gas it, just can't keep up the pressure? The filter is mounted on the frame rail, just behind the driver's door - cheap and easy to replace, and it's not going to hurt for sure... The fuel pressure regulator is the next suspect, which can be tested by pulling the vacuum line to see if fuel squirts out the vacuum line (that's not good). It should be a 'dry' experience with a change in idle...

Like WDE said - hopefully some of our resident experts will chime in soon. They can lead you down the right path much better than I can!

 

Thanks for your help alien. I’ll get to work on your suggestions in the morning. For sure this is an elderly vehicle and your suggestions can only help. Where can the fuel pressure regulator be found.

 

Not sure on the 300 - if sean chimes in he'll know for sure. On my 302 it's behind the intake manifold - just follow the fuel lines and look for the triangle shaped doodad!

 

The 4.9 doesn't have MAF unless it happens to be a California truck. I would try the engine running test, and check the TPS.

 

OK, I did the KOER test and got 2 codes.

536-Brake On/Off circuit failure/not activated
during KOER.
632-Transmission Control Switch circuit did not
change states during KOER self-test.

I need help interpreting these results. Could they be causing the ‘defective spark advance’ syndrome I am having?

I have not investigated the TPS yet. I’ll need to locate it first.

 

Did you step on the brake when the computer asked? That's why you got those codes, if you didn't.