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This is a 1998 Dodge Grand Caravan Sport, 3.3L 6-cyl MFI, which I bought recently.

In pursuit of the cause of 12 m.p.g. gas consumption, I am currently trying to diagnose the EGR valve.

Can you help me towards conclusive diagnosis based on the following set of my tests and observations?

Fuels consumption is about 12 mpg.
No leaks detected.
The engine runs very smoothly.
The outside of the end of the tail pipe is ringed with black soot.
Via a stethoscope, all of the fuel injectors sound to be operating rhythmically the same.

With the engine not running, I disconnected the vacuum hose from the EGR valve, and connected one end of a test hose in its place. When I sucked in at the other end of the test hose, I felt (with a finger end) that the EGR valve stem moved positively every time - it felt like by approximately 1/4 inch. While I kept the loose end of the test hose pinched-off, the EGR valve stem remained stationary in its new position. When I let air back in at the loose end of the test hose, the EGR valve stem moved back smartly to its starting position.

Next, I removed the test hose and reconnected the proper vacuum hose to the EGR valve. While I started the engine and let it idle for about a minute with the transmission in Neutral, i felt (with a finger tip) that the EGR valve stem did not move.

Next I cycled the engine speed, up to about 2000 rpm and back down to idle speed, several times. Sometimes I felt (with a finger tip) the EGR valve stem moving very slightly, in one direction as the engine speeded up and in the opposite direction as the engine speed returned to idling speed. Sometimes, however, the EGR valve stem did not move at all.

Finally, while I turned the engine off I felt that the EGR valve stem did not move.

Next, with the engine idling again, I disconnected the vacuum hose from the EGR valve, and I felt for vacuum (that is, suction) at the end if the hose using a finger tip. There was no vacuum, regardless of how I increased or decreased the engine revs.

For comparison, I temporarily disconnected a different, smaller-bore vacuum hose from the inlet manifold - and I did feel vacuum (that is suction) in it using my finger tip.

I have not tested, and I do not know how to test, the EGR backpressure transducer or the EGR solenoid.

I have not yet removed the oxygen sensors for inspection. I have been told that a white color would indicate sensor failure and need of replacement, whereas a brown color would indicate normal function.

I have not yet had the fuel pressure tested. Whereas I know that fuel pressure test gauges are available for sale, for example from auto parts stores, I'm wondering whether testing the fuel pressure might be a job best left to a professional mechanic.
 

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If the EGR valve is acting up you will get a rough idle due to it allowing exhaust gases into the intake during idle i.e. the EGR valve is open when it should be closed. If it remains closed instead of open, at operating speeds, you will likely get some preignition i.e. pinging.

My experience with a 1995 Caravan 3.3L was that I would get a check engine light with an EGR malfunction.

Have you checked your PCV valve for operation? Some reference material on the PCV valve:
http://www.mpgenhance.com/pcv_valve_fuel_economy.html
In today’s heavily computer controlled and adjusted vehicles a malfunctioning PCV valve can cause non optimal tuning characteristics via your engine’s management system that can contribute to reduced power and reduced fuel economy. Thus it is very important to check you PCV valve and replace it on a high mileage vehicle as it is often ignored.
http://www.agcoauto.com/content/news/p2_articleid/197
Another definitive test is to remove the vacuum hose and look for fresh oil. A PCV vacuum hose, with oil dripping or a wet valve usually suggest too much flow, which causes oil consumption. Checking the PCV vacuum hose is a wise precaution, on any engine that consumes oil.
EGR Valve: http://www.2carpros.com/questions/dodge-caravan-1999-dodge-caravan-egr-valve
 
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12mpg is crazy low. I can only think of two things that would cause that.

1. Transmission not going into overdrive/not shifting soon enough.. What rpms are you at when cruising at 60mph?
2. 100% stop and go city driving. Are you driving long distances and still only getting 12mpg?

Anything else and it would run horrible to be burning that much gas. Exhaust would be black and plugs would be fouled out within a week.
 
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Discussion Starter #4
If the EGR valve is acting up you will get a rough idle due to it allowing exhaust gases into the intake during idle i.e. the EGR valve is open when it should be closed. If it remains closed instead of open, at operating speeds, you will likely get some preignition i.e. pinging.

My experience with a 1995 Caravan 3.3L was that I would get a check engine light with an EGR malfunction.

Have you checked your PCV valve for operation? Some reference material on the PCV valve:



EGR Valve: http://www.2carpros.com/questions/dodge-caravan-1999-dodge-caravan-egr-valve
Sorry for the delay. (I was using a loaner vehicle, and I worked on this Grand Caravan only sporadically.)

First, responding to your comments:
- I don't experience either rough idle or pinging. The engine runs very smoothly.
- There is no engine check light.
- Since your post, I replaced the PCV valve with a new one.

Additionally, I replaced both O2 sensors with new ones.
The fuel consumption remains the same, at 12 mpg.

The EGR valve tests OK per the tests delineated in the Chilton repair manual.
A mechanic friend still advises me that the ECU must be making the fuel-air ratio too high due to erroneous interaction between the EGR valve and the ECU. He advises me to remove the inlet manifold and then clean out any gunk in the manifold, including around the location where the EGR valve attaches to the manifold. He believes that will restore proper interaction between the EGR valve and the ECU, and thereby fix the fuel consumption problem.
Any comments?
 

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Discussion Starter #5
12mpg is crazy low. I can only think of two things that would cause that.

1. Transmission not going into overdrive/not shifting soon enough.. What rpms are you at when cruising at 60mph?
2. 100% stop and go city driving. Are you driving long distances and still only getting 12mpg?

Anything else and it would run horrible to be burning that much gas. Exhaust would be black and plugs would be fouled out within a week.
Sorry for the delay. I was using a loaner vehicle; and I worked on this Grand Caravan Sport only sporadically.

Since your post, I replaced the PCV valve and both O2 sensors with new ones.
The fuel consumption remains the same, at 12 mpg.

Responding to your comments:
- I checked the RPM while cruising at 60 mph. It's been a few weeks, but from memory I seem to recall 2,500 rpm. I'll re-check it again tomorrow and amend this posting if necessary. Anyway, the engine seems fairly relaxed at that speed.
- Whereas my driving so far has been mostly local, it is not stop-and-go driving; and has also included some long trips to the airport.

The EGR valve tests OK per the tests delineated in the Chilton repair manual.
A mechanic friend still advises me that the ECU must be making the fuel-air ratio too high due to erroneous interaction between the EGR valve and the ECU. He advises me to remove the inlet manifold and then clean out any gunk in the manifold, including around the location where the EGR valve attaches to the manifold. He believes that will restore proper interaction between the EGR valve and the ECU, and thereby fix the fuel consumption problem.

First, when I get a chance soon, I intend to remove and examine one of the three readily accessible spark plugs (that is the front three).

Any comments?
 

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If the EGR valve is acting up you will get a rough idle due to it allowing exhaust gases into the intake during idle i.e. the EGR valve is open when it should be closed. If it remains closed instead of open, at operating speeds, you will likely get some preignition i.e. pinging.
I missed this post back in May.

No, a closed EGR will NOT ever cause preignition; ever. Preignition is where the intake charge ignites before the spark event, and it will virtually always destroy the engine with a few revolutions.

Pinging = Detonation

Detonation is when small pockets of end-gas (small pockets of intake charge) explode due to the pressure/heat of the fuel burn. That said, this is the first I have ever heard of a closed EGR causing detonation. Funny thing, many-many 3.3 and 3.8 liter engines were shipped from the factory, I've had two (of my four), and neither of them ever pinged or suffered from detonation.
 
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I checked the RPM while cruising at 60 mph. It's been a few weeks, but from memory I seem to recall 2,500 rpm. I'll re-check it again tomorrow and amend this posting if necessary. Anyway, the engine seems fairly relaxed at that speed.
Uhhh, 2,500 RPMs at 60 mph? Are you sure? That is WAY HIGH! At 2,500 RPMs, all of my 3.8 liter minivans would be running over 80 mph.
 
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- I checked the RPM while cruising at 60 mph. It's been a few weeks, but from memory I seem to recall 2,500 rpm. I'll re-check it again tomorrow and amend this posting if necessary.
My 2002 3.3L shows 2200 rpm at 110 km/hr (68 mph)
 
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I missed this post back in May.

No, a closed EGR will NOT ever cause preignition; ever. Preignition is where the intake charge ignites before the spark event, and it will virtually always destroy the engine with a few revolutions.

Pinging = Detonation

Detonation is when small pockets of end-gas (small pockets of intake charge) explode due to the pressure/heat of the fuel burn. That said, this is the first I have ever heard of a closed EGR causing detonation. Funny thing, many-many 3.3 and 3.8 liter engines were shipped from the factory, I've had two (of my four), and neither of them ever pinged or suffered from detonation.
Thanks. I should have said detonation instead of pre-ignition, the best description being "pinging". A faulty EGR valve and pinging seem to show up often when doing a search. This ARGO article explains the terms well and even throws in an EGR valve/pre-ignition association: http://www.agcoauto.com/content/news/p2_articleid/60
Exhaust-gas-recycle (EGR)

Exhaust-gas-recycle (EGR) is one system that helps to control pre-ignition and reduce emissions. EGR operates when conditions exist that cause pinging or valve clatter. A valve opens and circulates exhaust gas into the intake manifold to cool the combustion process. Exhaust gas is very low in oxygen. Adding exhaust gas to the fuel/air mixture, helps lower cylinder temperature. A lower temperature can help control pre-ignition and detonation. It does this, by raising the spontaneous combustion point of the fuel/air mixture in the cylinder. EGR also reduces oxides of nitrogen produced by pre-ignition. This makes it important as an emissions control device as well.
 

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Thanks. I should have said detonation instead of pre-ignition, the best description being "pinging". A faulty EGR valve and pinging seem to show up often when doing a search. This ARGO article explains the terms well and even throws in an EGR valve/pre-ignition association: http://www.agcoauto.com/content/news/p2_articleid/60
If the individual who wrote the Argo reference is unable to distinguish between detonation and preignition, then anything else written by said individual should be treated as HIGHLY SUSPECT!
 

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My 2002 3.3L shows 2200 rpm at 110 km/hr (68 mph)
Yup, and the 3.3 liter vans have a shorter gear ratio than the 3.8 liter vans; my 1999 T&C runs 72 mph when the tach is showing 2,200 RPMs.
 

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My 97 short van with 3.3 spins 1800rpm at 60 and I get 25 mpg on the highway avg up to 30mpg at 55mph. And that's when its 94 degrees and a/c blowing.
 
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My 97 short van with 3.3 spins 1800rpm at 60 and I get 25 mpg on the highway avg up to 30mpg at 55mph. And that's when its 94 degrees and a/c blowing.
Sounds like it has 3.8L gearing. 60/68 x 2050 = 1808 based on my 3.8L.
 

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Whenever one of my chrysler/dodge/plymouth vans has a gas mileage drop it has
always been the up stream oxygen sensor.
 

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Hotspur, I bet I got your problem figured out.
Youre not shifting into 4th/overdrive.
With my 3.3 van I run at 45 mph
1400 rpm in 4th or 2000 in 3rd
at 60mph 1900 in 4th or 2600 in 3rd
Since you said you ran 2500 at 60, you are not shifting into 4th gear.
That's why your mileage sucks.
At 2500 rpm in 4th I'm at 80mph and at 3000rpm I'm at 90 mph.
 
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Discussion Starter #16
Uhhh, 2,500 RPMs at 60 mph? Are you sure? That is WAY HIGH! At 2,500 RPMs, all of my 3.8 liter minivans would be running over 80 mph.
My apologies for not having rechecked the RPM vs MPH yesterday as hoped, which I had intended to do in order to correct (if necessary) the 2,500 rpm @ 60 mph that I wrote (on 07-25-2015 05:49 AM) that I thought I remembered from several weeks prior.
(For the last few days I had to disable a stuck-on rear wiper motor by removing a fuse; and doing that disabled the speedometer too.)

Anyway, I rechecked the actual rpm vs mph tonight, and here are the findings I was able to compile under the driving conditions that pertained tonight:

On level roads or downhill (in 4th gear, I believe):
1,400 rpm @ 45 mph; 2,000 rpm @ 60 mph; 2,400 rpm @70 mph; 2,600 rpm @80 mph;

On mild upward inclines (in 3rd gear, I believe):
2.100 rpm @ 45 mph; 2,500 rpm @ 60 mph

On a steeper inclines (in 2nd gear, I believe):
2,600 rpm @ 45 mph.

So at least it seems that my engine revs at speed are consistent with everyone else's here for the 3.3L engine.

By the way again, and as I wrote before, most of my driving recently has been about town, but certainly far from all stop and go. I would say that on such trips about town I'm usually in 4th gear coasting down hills or in either 1st, 2nd or 3rd gear while on the flat or going uphill at max speeds of about 40 mph to 45 mph.

My 12 mpg is still way too low, isn't it? And I think my gear shifting looks normal, doesn't it?
 

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Discussion Starter #17 (Edited)
Actual rpm vs mph

My 2002 3.3L shows 2200 rpm at 110 km/hr (68 mph)
My apologies for not having rechecked the RPM vs MPH yesterday as hoped, which I had intended to do in order to correct (if necessary) the 2,500 rpm @ 60 mph that I wrote (on 07-25-2015 05:49 AM) that I thought I remembered from several weeks prior.
(For the last few days I had to disable a stuck-on rear wiper motor by removing a fuse; and doing that disabled the speedometer too.)

Anyway, I rechecked the actual rpm vs mph tonight, and here are the findings I was able to compile under the driving conditions that pertained tonight:

On level roads or downhill (in 4th gear, I believe):
1,400 rpm @ 45 mph; 2,000 rpm @ 60 mph; 2,400 rpm @70 mph; 2,600 rpm @80 mph;

On mild upward inclines (in 3rd gear, I believe):
2.100 rpm @ 45 mph; 2,500 rpm @ 60 mph

On a steeper inclines (in 2nd gear, I believe):
2,600 rpm @ 45 mph.

So at least it seems that my engine revs at speed are consistent with everyone else's here for the 3.3L engine.

By the way again, and as I wrote before, most of my driving recently has been about town, but certainly far from all stop and go. I would say that on such trips about town I'm usually in 4th gear coasting down hills or in either 1st, 2nd or 3rd gear while on the flat or going uphill at max speeds of about 40 mph to 45 mph.

My 12 mpg is still way too low, isn't it, even though mine is the Grand Caravan Sport? And I think my gear shifting looks normal, doesn't it?
 

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Discussion Starter #18
Did replace O2 sensors - to no effect.

Whenever one of my chrysler/dodge/plymouth vans has a gas mileage drop it has
always been the up stream oxygen sensor.
I did replace both O2 sensors (see my post on 07-25-2015 05:49 AM). The mpg stayed at 12 mpg.
 

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Discussion Starter #19
Actual RPM vs MPH

Hotspur, I bet I got your problem figured out.
Youre not shifting into 4th/overdrive.
With my 3.3 van I run at 45 mph
1400 rpm in 4th or 2000 in 3rd
at 60mph 1900 in 4th or 2600 in 3rd
Since you said you ran 2500 at 60, you are not shifting into 4th gear.
That's why your mileage sucks.
At 2500 rpm in 4th I'm at 80mph and at 3000rpm I'm at 90 mph.
My apologies for not having rechecked the RPM vs MPH yesterday as hoped, which I had intended to do in order to correct (if necessary) the 2,500 rpm @ 60 mph that I wrote (on 07-25-2015 05:49 AM) that I thought I remembered from several weeks prior.
(For the last few days I had to disable a stuck-on rear wiper motor by removing a fuse; and doing that disabled the speedometer too.)

Anyway, I rechecked the actual rpm vs mph tonight, and here are the findings I was able to compile under the driving conditions that pertained tonight:

On level roads or downhill (in 4th gear, I believe):
1,400 rpm @ 45 mph; 2,000 rpm @ 60 mph; 2,400 rpm @70 mph; 2,600 rpm @80 mph;

On mild upward inclines (in 3rd gear, I believe):
2.100 rpm @ 45 mph; 2,500 rpm @ 60 mph

On a steeper inclines (in 2nd gear, I believe):
2,600 rpm @ 45 mph.

So at least it seems that my engine revs at speed are consistent with everyone else's here for the 3.3L engine.

By the way again, and as I wrote before, most of my driving recently has been about town, but certainly far from all stop and go. I would say that on such trips about town I'm usually in 4th gear coasting down hills or in either 1st, 2nd or 3rd gear while on the flat or going uphill at max speeds of about 40 mph to 45 mph.

My 12 mpg is still way too low, isn't it, even though mine is the Grand Caravan Sport? And I think my gear shifting looks normal, doesn't it?
 

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My apologies for not having rechecked the RPM vs MPH yesterday as hoped, which I had intended to do in order to correct (if necessary) the 2,500 rpm @ 60 mph that I wrote (on 07-25-2015 05:49 AM) that I thought I remembered from several weeks prior.
(For the last few days I had to disable a stuck-on rear wiper motor by removing a fuse; and doing that disabled the speedometer too.)

Anyway, I rechecked the actual rpm vs mph tonight, and here are the findings I was able to compile under the driving conditions that pertained tonight:

On level roads or downhill (in 4th gear, I believe):
1,400 rpm @ 45 mph; 2,000 rpm @ 60 mph; 2,400 rpm @70 mph; 2,600 rpm @80 mph;

On mild upward inclines (in 3rd gear, I believe):
2.100 rpm @ 45 mph; 2,500 rpm @ 60 mph

On a steeper inclines (in 2nd gear, I believe):
2,600 rpm @ 45 mph.

So at least it seems that my engine revs at speed are consistent with everyone else's here for the 3.3L engine.

By the way again, and as I wrote before, most of my driving recently has been about town, but certainly far from all stop and go. I would say that on such trips about town I'm usually in 4th gear coasting down hills or in either 1st, 2nd or 3rd gear while on the flat or going uphill at max speeds of about 40 mph to 45 mph.

My 12 mpg is still way too low, isn't it, even though mine is the Grand Caravan Sport? And I think my gear shifting looks normal, doesn't it?
Yeah, 12 mpg is way-way low. Our 1998 Grand Caravan Sport with a 3.8 never got worse than 17 mpg in Manhattan traffic.

I'd be looking to replace the upstream O2 sensor if I were in your shoes (don't use one from Bosch).
 
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