Doesn't make sense MAF or pump

[rocco123]

I just made it home from work after stalling many times , poor acceleration & poor idle. My '94 with 4.0 did get me home though. When going Key On Eng Off the fuel pump sounds like it's sucking air with a cavitating sound before eventually coming up to pressure & turning off (like it should). The sucking air sound made me fell like "great...I gotta change the damn pump". When checking codes I get 157, 158, & 159 all pointing to the MAF. Cleaned the MAF & it still runs bad & the pump sucking air sound continues with eng running or just KOEO.

Disconnect the MAF & the thing idles fine. I know, I know... change the MAF & see what happens. I just don't understand what the cavitation sound is in the pump area whick goes away only when the MAF is disconnected.

BTW... I do remember some time ago running the eng with the MAF disconnected & it always ran / idled terrible. Right now it doesn't run too bad with it disconnected (still have the CEL though)


Any ideas?

 

[mikeinri]

Start with cleaning the MAF to at least get that problem out of the way (cheap and easy).

The pump issue may be an unrelated coincidence.

Mike

 

[rocco123]

Cleaned it twice.. 1st time W/carb cleaner, 2nd w/alcohol & a q-tip . Problem did not go away. Ran a jumper to give a batter batt ground from neg to alternator housing....no fix.

 

[fordnut71]

sounds like 1 of the wires has broken inside the housing. have a look into the sample tube an see if the wire is still hooked on both ends. will kinda look like how a light bulb is wired up. if it looks ok just give a lil shake an look to see if the wire isnt wiggling in there.

 

[MrShorty]

EEC-IV isn't always very smart. Sometimes an MAF code (especially CM codes -- you didn't state which part of the test those came from) means that the computer is having trouble reconciling the sensor(s) values with the measured "mixture" at the O2 sensor. If those are CM codes and the fuel pump is making "wierd" noises, I might start by testing fuel pressure to see if fuel delivery is up to spec.

 

[mikeinri]

Sorry, read that too quickly and didn't see that you had cleaned the MAF already.

MrShorty always has great advice on these things.

The other thing that I would do is get a troubleshooting guide for those codes, just to rule out that they are real. If you take the codes to autozone, they can print out a detailed troubleshooting guide, including voltage checks for each wire in the affected circuit.

Hope this helps.

Mike

 

[rocco123]

Thanks for the responses. Naked eye visual insp appears both elements are attached, but under a 100 X it looks like the taller heating element (filament) has crusty stuff on it, and may be bare in some spots...really can't make it out. Resistance across both pares of element legs shows 20.9 ohms. Wish I knew what the resistance should be at the connector. Will check this morning to see if fuel pressure is good. I suspect it would be as it runs OK with the MAF disconnected. Do you agree that it should run normally run bad with the MAF disconnected?

 

[mikeinri]

I can't recall, it's been a while. I had a disconneted MAF once, after some idiot at a quick-change oil place broke it on me (anyone could have done it, the idiotic part was not telling me about it). It threw codes, but I can't remember how it ran.

Previously, I had a bad MAF that I ignored for a long time. It made the engine run so poorly that it eventually clogged O2 sensors, etc. and was blowing soot out the tailpipe. THAT got expensive...

Mike

 

[wood1]

I just made it home from work after stalling many times , poor acceleration & poor idle. My '94 with 4.0 did get me home though. When going Key On Eng Off the fuel pump sounds like it's sucking air with a cavitating sound before eventually coming up to pressure & turning off (like it should). The sucking air sound made me fell like "great...I gotta change the damn pump". When checking codes I get 157, 158, & 159 all pointing to the MAF. Cleaned the MAF & it still runs bad & the pump sucking air sound continues with eng running or just KOEO.

Disconnect the MAF & the thing idles fine. I know, I know... change the MAF & see what happens. I just don't understand what the cavitation sound is in the pump area whick goes away only when the MAF is disconnected.

BTW... I do remember some time ago running the eng with the MAF disconnected & it always ran / idled terrible. Right now it doesn't run too bad with it disconnected (still have the CEL though)


Any ideas?

The sound that you describe coming from the pump makes me wonder if the rubber hose coming from the pump (inside the tank) has a crack or split in it or something.

Just an idea, not much I can come up with to suggest to verify that other than dropping the tank. Maybe if you checked the pressure at the rail while driving, but that might be difficult.

 

[fordnut71]

maybe the fuel filter is pluged up?

 

[rocco123]

Changed the filter a couple of years ago. Just installed a MAF from the scrap yard. It stays running, but still kicks the CEL. Went home & found it's a new code (33) which now points to the EGR system. EGR diaphragm holds vacuum, but the valve just before the EGR (supplying the vac) allows vacuum both ways. Loked like it takes 12 volts to maybe close it...as that's what i read to that valve with the ignition on, so I put it on the bench & thought it a good idea to see what it does with 12 volts applied. BIG smoke storm coming from my test leads. Whatheheck? Though this was just a vacuum relay for the EGR control? No click or nothing...just smoked leads that should have easily carried the current.

Right now I capped the vac line to the EGR & put it back together. Still kicking a cel, but at least I'm confident I'll get to work tomorrow. Every once in a while it will hiccup & drop power like a ignition short, but other than that it runs.

Still need to verify correct fuel pressure...maybe borrow a friends gauge.

 

[MrShorty]

Are you sure it isn't a 111 code? As evidenced by the first set of codes your reported, your '94 should be outputting 3 digit codes.

If it is a 33x code, which would point to the EGR system, be sure to specify if it's a KOEO or CM code -- Diagnosis of EGR codes often depends on which type of code it is.

 

[boggs1227]

you may want to look at my threads "iac ohms test" and the newest one " erg problems " that is if you haveing egr problems .i was / am haveing problem with the dpfe module and the egr postion solinoid.i am kinda haveing the same symptoms you got ...drop in power while driveing ,bad idle ,etc... . my maf is fine but if your throwing a egr code ...then read my threads ...may help . but if you hooked up the egr solinoid and got smoke from the leads then i would wonder if you did not fry the part .......

 

[rocco123]

Don't think I fried the part, but there could have been a diode in the valve and I hot wired it wrong (Haynes doesn't show this valve). The code 33 I'm reading is key on engine off. Kicks out 33 twice, which the manual say it would. Haynes says it's egr related. Will look into that tonight. Idles terrible this morning (not in the warm garage like all day yesterday). Seems to now have what sounds like an exhaust leak underneath too. This damn thing is going down hill fast, and I don't want it to throw good money at something that I may have to get rid of.

 

[boggs1227]

yeah i know how you feel about that...when i first bought mine i tried for a month to get it started and stay running and there was about 3 times i was ready to throw in the towle and just sell it off and recoup what money i put into it at the time but it paid off in the long run .but very few trucks ( like the explorer) last for such a long time ....with proper care it could live longer.

...i like the explorer better in a lot of ways better than i do my new chevy truck and its 14 going on 15 years old ! you got to expect things to go wrong and fail from time to time ,it's all par for the course .

 

[fordnut71]

sounds like the transfer tube from the exhaust to the egr is broken an that would explain some of your problem.if the exhaust is broken the dpfe is getting a rich lean condition causing a conflick with the other reading the computer is getting.

 

[boggs1227]

that actually makes sence....i think devilboy222 had a similar problem with this egr tube and had to replace it because it had rusted out completly. that alone would give you a exhaust leak sound ...cause it is .......

 

[rocco123]

tube to the egr is good. I welded a new flange back on it a few months ago when I replaced the lower intake gasket. DPFE was replaced about 4 years ago. The 2 lines are connected & in relatively good shape. The nipples on the DPFE lines tend to corrode right off, but mine is still good. I'll head to the junkyard this weekend to look for a servicable EGR.

BTW..confirmed an exhaust leak on the top of the muffler. Big problem is where I'll get time to work on all this.

 

[fordnut71]

did you find out what was causing the problem or are you still having it?

 

[rocco123]

After confirming the code by checking the MAF output voltage I replaced the MAF & fixed it. The MAF I pulled from the boneyard was bad. Voltage to the sensor when hooked up & running was 12v between pins A&B(supposed to be at least 10.5 v) ..no problem with that. The voltage read between pins C&D supposed to be between .34 to 1.96 V per Autozone's website repair guide. I was gotting zero one time, then after sitting a day I hooked it up just before heading to a store to get a replacement I read 1.3 v & it ran OK...drove it around 1/2 block got the CEL. Brought it back home & read just over 4 volts on pins C&D (again, with it installed). Replaced the assembly disconnected the battery for 5 min, hooked it all back up & drove it a few times with no CEL & no rough running.

In the meantime I did check fuel pressure per the Haynes manual (incl disconnecting the vack line to the regualtor) & it all worked as advertised. Checked compression thinking it could possibly be a broke valve spring, and read 150 - 160# on all cylinders.

Changed the leaking radiator, & still need to change the muffler sometime. Not sure what the noise was from the fuel pump.

I thank all of you guys for the assistance & ideas on this issue.