I have a 1989 e150 with the 302 and 4AOD that's been sitting for close to a year now. I've started it up every few months but hadn't actually driven it til the other day. It revs seemingly fine in park but after driving it I realized when I give it gas the engine falls on its face, stumbles, and makes an a-rhythmic knocking sound. I've never experienced pinging in an engine but it might be this. I put a few gallons of fresh gas in an almost empty tank and the problem persists. If I get a little momentum and the engine doesnt have to work as hard to continue rolling the knocking sound goes away but as soon as there's more load on the engine it the pinging returns and the engine is shaking quite a bit. There are rats out here that can cause problems with wires and vacuum lines but I looked pretty thoroughly and couldn't find any damaged wires or hoses. I checked for codes and came back with 41 77 and 52. One or two of those is me not doing the whole pump the brakes, put on the gas and turn the wheel I believe? And one is low/no voltage from the o2 sensor if I remember correctly. Wires to the sensor look fine, The O2 sensor has about 4000 miles on it. Maybe I didn't warm up the engine enough before taking the test and got that one? Spark plugs, wires, cap and rotor all have about 4000 miles on them as well. I disconnected the battery for some time and ran it again, still did the knock and loss of power when under load. Curious what people think might be causing this issue as I'm sort of at a loss at this point. Thanks!

 

Well I seemed to have figured something out. If I disconnect the wiring harness to the MAP sensor the issue almost goes away but it is still weak under load and tends to stall when I first put it into drive. Once I start it up again and put it in drive I can cruise around with more power and almost no popping sounds. Any ideas based on these new findings?

 

Here's a link to a video of the sound. When I push down the gas pedal the engine shakes and loses power and the popping/banging sound starts happening.

https://imgur.com/a/XhkpFTM

 

You have a miss
Does it have dual fuel tanks?
Your miss could be caused by a whole bunch of different things
First up is the tune up and plug wires, cap and rotor
I would also check the codes (just in case) and check the fuel pressure for sure
Pre 1990 FORD vehicles have both low pressure in tank pumps, and a high pressure chassis pump
If it runs ok at idle, the pumps may be okay but the delivery through the crossover valve may be insufficient
Yours will not have the pesky crossover valve if no dual tanks
Good luck
Drive the van around with a fuel pressure gauge on it (taped to the windshield, so you can see it while driving)
Run it around with a vacuum gauge on the intake manifold too
If the exhaust is plugged, basically you will see it hard to maintain good vacuum (15 inches) when floored

 

Hi,
I have almost the same van (90)
do you have the equipment to check the gas pressure ? I'd look that way if I were you (should be by 40/45 psi I guess, I'm sure experts here will soon confirm or correct)

edit: manicmechanic007 is ahead of me ! but now you kwow which way to dig

 

Right, those 4.9's have higher fuel pressure 45-60 IIRR
Where the V8's are 30-35
I think his fuel pressure might be okay because it starts fine and runs at idle
His problem is the injectors or plugged exhaust IMO
But
Damn sure test the fuel pressure, and check the fuel pressure regulator for any fuel coming out the vacuum hose

 

302 is a V8

 

My van does have duel tanks. I've yet to notice a difference when switching between the two tanks. The only thing I've done thats made a meaningful difference to how it runs is unplugging the wiring harnesses to the MAP sensor.

Here’s a video of the fuel pressure under load:
https://imgur.com/a/Hej6Rht

Here’s a video of it hooked up to a vacuum gauge under load and at the end at idle: https://imgur.com/a/87ujijF

Obviously vacuum reading is troubling but I'm not sure what its telling me is wrong.

Also the plugs show its running rich:

 

I just discovered that disconnecting the vacuum line to the EGR valve eliminates the symptoms. Appears to be an EGR malfunction but not sure what the source of the issue is.

edit: false alarm, symptoms persist, just ran better with the EGR unplugged.

 

The vacuum gauge reading looks like to me you have either plugged exhaust or low fuel pressure
What goes in, must come out
Have an assistant rev the engine (or try to rev the engine), then check how much exhaust is coming out of the tailpipe
When you have plugged exhaust (plugged cat) or (broken catalyst material in the muffler), there will not be much exhaust exiting the tailpipe
When the engine is idling fine at 15 inches of mercury and you stab the gas, that vacuum should go to zero momentarily, then shoot right back up to 15 as the engine revs up
If it stays around 5 your exhaust is plugged, it's deceiving sometimes as low fuel pressure will cause the same thing
So, check the fuel pressure as you do the vacuum tests
Good luck

 

ok I will investigate the exhaust today. Do you think unplugging the MAP sensor would have any affect on the issue if it were a plugged exhaust? That’s the thing that keeps me scratching my head, that unplugging the MAP sensor gives it a lot more power and it can climb hills with much more ease with the MAP unplugged.

 

Well, it might have just thrown itself into open loop operation with the MAP unplugged
That fattens up the mixture
The engine can also run on data tables if a sensor is disconnected
Some sensors have data tables, and I believe the MAP is one of them

 

the thought that the computer can fix the issue by adjusting the mixture makes me question if it’s a something mechanical like a exhaust blockage or weak fuel pumps. I’m suspecting something by electrical like bad ground, bad sensor, wire chewed by a rat somewhere. It doesn’t help at all that the computer isn’t showing any codes. I unplugged the o2 sensor and the check engine light didn’t come on. Maybe that’s normal but when I’ve unplugged other sensors the light will come on. I might have a look at the computer board today just in case a capacitor has leaked and I’ll try to check the status of all the grounds.

 

Have you ever pulled the computer and had the capacitors replaced.