Hi all,
We have a 1991 Aerostar with 95k mi. 3.0l Now will barely idle (cold or hot) gulping fuel and lost 50% of power. Surges, pings a little, chuggs. Engine rocks at idle. We are good mechanics but stumped. It has always FELT like it had a big vacuum leak, and still feels like it, but I can't find one. Last year it started to accelerate a little rough, but has always been
very smooth on the highway. Last week it degraded quickly to barely runable. Now it fires up easily but often dies right away, or lopes badly or surges. Takes a lot of gas pedal to get it moving or keep it idling. When revved up it humms smoothly and sounds even, but getting it moving is tough. Stalls too often. Checked vacuum lines thoroughly, and sprayed every inch.
Nothing. New plugs, wires. Improved little. #1,2,3 had light white coating, the rest were worn but normal color. Have replaced fuel filter and pressure reg.(wasn't much latent fuel pressure) Have pulled the IAC and cleaned but no change, it also does not fully seal closed--is this normal? (Two I grabbed from the bone yard were the same). There is no EGR, no MAF. Checked codes, none. Will soon do key-on check. From 20ft away I can hear it make a huge air-sucking sound (louder than normal) at idle which actually normalizes as it revs up. There are some minor exhaust leaks. Has been using a lot of oil, but no smoke or leaks. No tapping or ticking. My very first thought was the IAC.
Any ideas?

 

welcome docbrotherman

sounds like lower intake manifold/head air/vacuum leak gasket leak on passenger side of engine. may also be leaking coolant into the cylinders on pass side because of white coating on those 3 plugs.

try spraying with a carb cleaner and nozzle tube around suspected leak areas. can also try retorquing the intake manifold lower and upper bolts. these do work loose. if you do find a leak there, best to replace the gaskets with new and torque all to specs.

how much oil is the engine using? blue smoke out the tail pipe?

the IAC only goes closed completely when engine turned off or IAC unplugged.

 

I has sprayed almost every inch of the engine with carb cleaner with no result. I even checked to see if there was suction into the crankcase. None. It seems to use a quart per tank, but no serious leaks and no smoke at all. I just replaced the muffler, as it was shot full of holes, but there was no oil residue anywhere under the car as might be expected.

It seems that the injectors only want to kick in when the manifold vacuum is greatly reduced having me suspect that there is a vacuum sensor somewhere that is bad.

The IAC does not close completely when off, unless I remove the solenoid. The two I got from the junk yard were the same.

Can anyone tell me what the fuel pressure ought to be, and if there is a vacuum sensor?

 

The fuel pressure should be 35-40 psi; lower at idle, and higher at open throttle. The regulator should have a manifold vacuum line on it to change the pressure with the engine load. I guess it's hard to get a manifold vacuum reading when the engine is surging like that. You may have a manifold leak on the INSIDE of the manifold, sucking in oil. That's rather unusual, but not impossible. It may have been getting worse over the last year, giving you the increasingly sever symptoms that you've experienced. You won't be able to detect that with spraying carb cleaner on the outside. The only way to know for sure is to pull the intake manifold. Of course, if you do that, you will have to replace the gaskets regardless. However, a lot of members of this forum have found the lower intake manifold gasket leaking after a few years, so it's not a bad idea to replace it. Do you have external oil leaks from the lower intake areas?

 

is there any smell of raw gas in the exhaust?
if so, check the vacuum line to the fuel pressure regulator on top of the intake manifold. the diaphram on the FPR breaks down from fuel and movement after years of use and cracks, leaking pressuried gas directly into the intake manifold. will cause major idling and up to mid power issues. the excess raw unatomized gasoline with run down past the rings into the crankcase, thinning the oil and causing far more oil burnoff and suck off thru the PVC system

can also be the vacuum line running down to the transmission vacuum modulator on the passenger side of the tranny. they break and leak in lots of excessive air.


there should be a slight vacuum in the crankcase for correct PCV system operation.

 

Hi, Docbro... - Like xlt4wd90 said, I've had that rare internal vacuum leak because the intake manifold wasn't seated properly, from when the PO had the engine ('89 3.0 V-6) rebuilt. On my block, there is a gap under the manifold, where you can see the camshaft and the crank below. Check that your intake manifold vacuum is 16 inHG or so at idle for major vacuum leak. When mine measured only 12 inHG, I searched thoroughly for leaks externally (hoses and components) and couldn't find anything. When I took off the intake manifold, I could see that air was being sucked up from the crankcase by the oil vapor traces. Mine was using oil as well (a quart every 500 miles) with very little exhaust smoke, which was driving me crazy cuz' I couldn't find any leaks and the engine had just been rebuilt.

If you have coolant or oil fouling your plugs (#1,2,3), look at your oxygen sensor for any contamination. Fouling on this sensor will mess up your computer's ability to constantly adjust your air/fuel mix. Could be other sensors failing as well, coolant temp. or the MAP (manifold air pressure sensor). It's a drag you're not getting any codes, which my OBD1 gave from O2 sensor oil fouling.

With the major vacuum leak, still my van ran well, just surging at idle and using oil. Maybe a couple of things are confusing your situation or the manifold interior vacuum leak has become considerable. I wonder if you have a restricted catalytic converter.

Good hunting, Mike

 

I did not think of a blocked exhaust.
The TPS gave a bad reading yesterday. The input wire was only .03v and the ground wire was 12v (sometimes) but gave wildly swing readings at other times.
My thinking might be flawed, but I checked for a leak into the crankcase by seeing if there was any vacuum at the oil filler spout. (not a bit)
We are about to do a key on test.
Is the MAP sensor the one on the drivers side of the plenum toward the back?

 

Hi, docbro... If your setup is like mine, MAP is mounted on the firewall directly above the engine, very close to the hood opening. On my plenum (throttle body?) midway driver side, there is an air charge temperature sensor. On the front upper surface of the intake manifold is where your coolant temperature sensor (two if you have an digital dashboard) is/are. Other culprits could be your O2 sensor (just before catalytic converter; some setups have two), vapor canister purge solenoid (above block, down in all the assorted tubes around the fuel pressure regulator), your transmission modulator (passenger side of trany, 'conveniently' located behind exhaust piping. These could effect your air/fuel mix (bad/poor signals to computer) or be a source of vacuum leak or air/fuel mix contamination.

TPS could be the source of bad signals if out of whack (bad idle and rough acceleration), and apparently so can the speed sensor (mounted on transmission on mine, driver side of trany, towards the rear).

Yeah, go for any/all codes in different modes. There could be codes stored in the computer memory, etc. I have an ol' Equus code reader (model #3145) for Ford vehicles with OBD1 systems; It's cheap and very effective - I used it for years on my van and F150s, etc.

The reason I mentioned the blocked exhaust is the loss of power, dies right away after start-up and stalling too often; This is after checking your fuel supply and ignition first, which it sounds like you've done. The other stuff (surging bad idle, oil consumption) reminds me of my internal vacuum leaks between the intake manifold and heads - take a read with an ol' vacuum gauge just to see. Also, were those slightly fouled plugs dusted with a white coating (possible contamination) or were they showing signs of lean burning on that bank only.

Good hunting, Mike

 

Thank you to all that put in a good word to help. It turned out to be the MAP sensor. Once we had pulled the vacuum line off of it, the van immediately idled smoothly. $50 later (thank you O'reillys) it was back running 100%

It still uses too much oil (still a mystery) 400 miles on a quart.

I still wonder about the right bank cylinders spark plugs with their white dusting. I will know more after pulling the new plugs out after it runns for a few weeks.

Good luck all.

 

Yup - Just one sensor.... Your oil consumption is bizarre, like mine was... Same amount - 500 miles or so on a litre. Have you tried cinching down your intake manifold and throttle body, or taking a intake vacuum reading (see my first post on this thread - you may be surprised); I was.

Good to see you're getting there, Mike

 

Now that it is running decent, I can get a vacuum reading. The strange plug residue still has me concerned so I'm gonna keep on it.

 

Hi, Docbro - I can't attach photos to my posts, but, I created an album - 'my 1989 3.0 Eddie custom'. Photos 6 & 7 show how the engine rebuilders gooped up the intake manifold around the water passages and manifold seals. This 'goop' didn't allow the manifold to seat itself properly on the block between the heads - the coolant passages didn't leak, but all the fuel/air intakes showed oil mist trails from the crankcase opening below. This was the source of my major vacuum leak and high oil consumption. When I installed new gaskets w/ much less sealant, both problems were solved immediately.

Cheers, Mike