Ok, so I have a 1988 aerostar, 3.0, auto, 4.10 gears.

I was having bad spark knock when the transmission shifted into od on level roads with light throttle. Uphill and accelerating in od...forget it.

I read a post (I think on this forum, but not sure) so filled up with midgrade. Noticed the following.

1. No more spark knock when shifting to od. Only light rattle when accelerating uphill, but not maintaining speed uphill or accelerating on level roads.

2. Smoother running engine. Like buttah.

3. Better mileage. The trip computer used to report avg mpg as in the low to mid 15s. Now it shows 16.3.

I have some ideas.

1. Ford build the engine right on the edge of 87 octane's anti knock abilities. The weight of the van over the Taurus (my cousin has a 97 with the same engine...sorta...and no knocking) would mean it has to work harder and might be JUST too much without better gas. Since I have read about other people having the same issue and results, I think I may be onto something.

2. My engine has carbon built up in the cylinders.

Probably a little of column a and a little of column b. Midgrade doesn't cost that much more than regular, and is offset by the better mpg, so I'll keep using it.

Any thoughts on my thoughts.

 

I came to this same conclusion with an `89 Taurus SLO I had for 8 years. Try a higher octane next fill and see if the pinging is less or completely goes away.....

 

Hi, BigLoo - spark knock (detonation), eh? I have an '89 3.0 EB, auto - extended, so our rigs and engine control systems should be very similar. I don't have an EGR or Knock sensor, so I doubt you do too. I run octane 87, but, I try to use a 'quality' gas, which should have additives that help clean your engine, but... I don't have bad spark knock, so...

Some other causes of spark knock; engine overheating, engine carbon buildup, engine rebuild (compression ratio - too high), over advanced ignition timing, cheap gas, lean fuel condition. I know 89 octane gas is working for you, but, I believe there is probably a root cause for your issue. I've always used 'quality' 87 octane gas, for the most part. When I first got the Aero', I had some annoying knock. After tuneup, re/re some sensors, operating changes, etc., it is under control.

Cheer, Mike

 

Well...I got this van extremely used, so I have no idea what has (or, more importantly, has NOT) been done to it. I would be more likely to guess carbon buildup than anything else. I seriously doubt that the engine has been rebuilt, and the compression ratio is probably what it's supposed to be (minus the "carbon boost").

I use the same gas I've always used, and never had any problems in any other car, so I'm going to go ahead and eliminate that. I try to avoid rinky-dink convenience stores that also happen to sell gas. I usually go to 7-11. Again, never hap problems with it before.

Maybe some SeaFoam will help.

 

Seafoam will work to a certain degree but this stuff can make a night and day difference. I used these on my 88k mile `92 SHO yesterday. I am still amazed what two cans of cleaner did for mileage, power, and overall runability.....

This:
http://justbgit.com/BGFocusOnFuel/picts/210C.gif

Then this:
http://www.bgprod.co.uk/images/Products/206.ht1.jpg

 

The 91 extended 2wd van with 4.0L engine I bought in 2006 had severe knocking under load, while my 1990 ext/awd did not, even though it weighed more. I tried higher octane fuel and all sorts of chemical cleaning fluids, in the tank, directly in the intake manifold and fuel rail, but the knocking persisted. The knocking van also barely passed the HC part of the emissions test, so it was running way too rich. Normally, running rich helps prevent knock, but it turned out in this case, the previous owners must have done some terrible things besides neglect. I found severe carbon build up on the spark plugs, a couple of which had experienced so much detonation that most of their electrodes had disintegrated. So I replaced those, and the HEGO sensor, just to make sure that at least that part of the engine control is working properly. I ran that for 3 years on 87 fuel, with no hint of knocking, when I sold it.

So I agree with Mike; you need to find out what is the fundamental cause of the knocking and try to fix that. The timing is the first thing I would check, then the spark plugs. You could also try the de-carboning process that has been posted:

https://www.ford-trucks.com/forums/7...ning-4-0l.html

 

the OHV 4.0L Ford with the standard heads prior to the '97 are notorious for carbon buildup.
just decarboned mine after not doing it for several years, just an on street parked spare dog van now. only slow speed urban/suburan trips, seldom on the freeway.
engine runs much freer now, acelerates and sounds much better.
these build up carbon in the ring grooves also, jacking the rings out against the cly walls increasing friction.

make my own homebrew seafoam. 70% paint store acetone, 28% kerosene, 2% paint store MEK.

be prepared for shocking amounts of white smoke and carbon blown out, mine must have had a load in the CAT and muffler also. restrictive quiet Walker since I hate a booming muffler in a van.

sure made a freeway onramp bomb out of it now. runs like it did new off the lot

never have had a knock problem in this one even towing heavy 8800 lbs GCVW in the Rockys and desert heat.
always ran regular 87O
4.0Ls are known for their weak crack prone heads so any engine cyl. knock is head death.

 

I don't know if you've posted about this problem before, so forgive me if this has been done, but give it a tuneup. It's possible that the spark plugs have some glowing sharp edges or some carbon on them that remains hot. My 4.0 used to have a persistent ping to it and it was cured with new plugs.
Like you posted, you could always keep running 89 octane in it. My Mark VIII needs premium fuel and my local gas station sells 89 for the same price as 87, although I suspect it has just more alcohol in it.

 

Look, this engine was not built on the limits for 87 octane. If your engine is pinging and knocking, its because something is wrong. With the age and mileage, it can be anything from vacuum leaks, dirty MAF if equipped, wrong plugs, carbon build up, etc. Running a higher octane than the engine requires, even if its to resolve a problem that is causing pinging, will over time cause additional carbon deposits, which in turn can cause more pinging. Better to fix the cause of the problem than to band aid it with a higher octane fuel.

The 3.0L is not known to knock, so if yours does, something is very wrong.

 

Hi, BigLoo - Sounds like you got some work ahead of ya'. Start with the easy stuff; check timing, check plug condition, read computer codes, tune-up (+ decarbonizing), check fluid contamination/condition, vacuum leaks, etc. All round diagnostics and general maintenance, as needed. It sounds like your 'extremely used' van needs some TLC. It could be something simple, or a combination of things - you gotta just work it out. Like you said, what hasn't been done by the PO, is most likely the problem (ie. tune-ups, regular maintenance, etc.), so you're starting from the beginning. By the way, I doubt your van has a MAF; my early 3.0 has a MAP, so yours' probably will too.

Cheers, Mike

 

Correct, Mike, my van is speedNdensity (I.e. MAP sensor) not mass air.

the van does need tlc, and has gotten quite a bit. She still needs more, though. The body is in good shape, and it runs too well for there to be MAJOR problems...just an accumulation of minor oes (which, if not corrected, will lead to major ones).

I am leaning heavily toward carbon buildup, and will seafoam it on payday. I also seem to recall something about the computer being changed when it wasn't running, trying to get it running. Possibly the wrong ECM?

I dunno...I'll find it. I am off work starting tommorow til january 3.

 

Your engine should have a distributor. If its not aligned correctly, you could get excessive advance.

 

or the distributor shaft and/or cam/dist. gears are worn, throwing off timing at higher rpms or under load. seen that one happen lots of times on old SB Chebbys and Ford Y block V8s.

I'm betting on carbon build up hot spots.