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Discussion Starter · #1 ·
Hi, I have this odd problem with my '88 LeBaron 2.2 turbo - while the gas mileage starts out great on a highway drive (28-30 MPG), after about 45 minutes on the road, the MPG drops to about 18 to 20 MPG. This is as measured from the dashboard trip computer, but it is consistant with calculating the miles per gallon after I fill up too.

To back up just a bit, I bought the 88 LeBaron with only 61,500 miles on it a year and a half ago from a guy that was pretty much a maintenance fanatic. The car is still very original and in great running shape. There are no mods to the car and I'll be keeping it that way. The car has done this from the time I bought it.

It's just a bit frustrating that the gas mileage drops like that over the duration of the trip. I'd be happy if I could get 26-30 MPG while driving the whole 3 hour trip!

Anybody else ever seen this kind of drop in mileage and figured out what caused it? Thanks for any help you might provide!
 

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Could be the fluid is breaking down after it heats up, maybe time for a change, and maybe a cooler while you're at it.
+1 here

Has all the shift kit stuff been done yet? It could be slipping more once it gets hot.

Too hot of plugs can cause detonation once the engine gets good and hot without an intercooler. A colder plug can help. Try running plus fuel if your running 87 now.
 

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Fault codes stored?

To me, it sounds like the computer is adding extra fuel once you are 45 mins into a drive. Could be heat/sensor related - something is causing the computer to think more fuel is necessary. A scanner to check voltages once you are up to temp would help. Could also be a ground that loses good contact once enough heat soak has occurred from current/underhood temps.
 

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Could also be a bad vacuum line to the FPR, or the FPR itself, would be nice if you could check fuel pressure once the MPGs drop off. Could be something heat soaking and causing a vacuum leak, like a loose fitting in the manifold or maybe even a vacuum line going soft from the heat and the collapsing.
 

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is this always happening along the same route ?

I ask because of somthing I noticed while helping a buddy move

driveing from toronto to barie (north of t-o) my 86 turbo z got about low to mid 20's mpg going to barie - comeing back I got about 28 - 32 (stock log motor)

this is because barie is at a higher elivation than toronto so eventhough you can't see it you would be driveing up hill to get to barie

so , what is the mileage like on the return trip ?

agreed though getting 18-20 sounds like something is wrong with the car as that's pretty low - I'd wonder if you have an injector that dribbles gas once heat soaked
 

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Discussion Starter · #10 ·
Awesome - lots of good suggestions for places to look.

I'll try to reply to the questions here:
- "Could be the fluid is breaking down after it heats up, maybe time for a change": Could be, I guess. The transmission fluid is full and seems OK. Doesn't look or smell bad, but as you suggest - that's not always the full story. I'll probably try changing that, but it certainly isn't slipping. The revs needed to keep the car at speed never change.

- "Does it increase again if you stop and let it cool down a bit?": Yes! if I stop about 1/2 way home and let it cool down, after about 30 minutes it returns to the best mileage (28-30 MPG), then falls off again about 30 minutes later.

- "Has all the shift kit stuff been done yet? It could be slipping more once it gets hot. <p> Too hot of plugs can cause detonation once the engine gets good and hot without an intercooler. A colder plug can help. Try running plus fuel if your running 87 now.": As far as I know, nothing's been done to the transmission, certainly no shift kit stuff as (looking through the glove box, this thing's always been owned by women - no dig there, just thinking that no guys have tried to "improve" it yet!). Like I say, though, the revs to keep at speed never increase. Yes, it always runs hot in my opinion, the bar gauge is always above 1/2 way up there (digital gauge), but like you said, I'd written that off to the turbo with no intercooler. Never thought of changing plugs. I'll have to tend to that this year. I do always put the highest octane I can get into it - just cause the owner's manual in the glove box said to... I'll have to look into the plug heat ranges.

- "Fault codes stored?": Guess I have a lot to learn here too. I've never had it "read". Is there a way to get the fault codes without a gadget to hook up to it? I have a 92 LeBaron too (no fetish here - honest, it's a long story) that flashes the codes with a certain key sequence - does the 88 do that too? I'll have to check into the codes by having Advance Auto Parts read em, I guess... Great suggestion on the grounds in the engine compartment! I hadn't considered that but will look at those. I have seen faulty ground cause havoc.

- "Could also be a bad vacuum line to the FPR ... loose fitting in the manifold or maybe even a vacuum line going soft from the heat and the collapsing": Lots of great thoughts there. It's so clean under the hood (the top part anyway) that I'd not thought of looking at those details. I'll have to do that! It's worth checking - a close inspection is needed.

- "is this always happening along the same route": Happens in both directions on the same route, (Going to see Dad) so I'd ruled out that possiblity, thinking it would average out. You can really see the MPG drop on the onboard trip computer when it happens... Hadn't considered of an injector problem, but that's a good thought! Any way to check those?


I'll be taking a look this week and see what I can report.

Thanks for your help!

JK
 

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Fault retrieval sequence is simple. If there are faults stored in the system you will know...

With the car off, cycle the key to the "on" position (but do not crank car over) three times. Ex: on-off-on-off-on-off. You do not have to do this with lightning speed, just casually...

After turning it back to "off" the third time, watch the check engine light. It will start to blink. You will count the blinks and equate that to a number. Blinks that occur together with short intervals represent a number. A longer pause between blinks means a new number is being indicated. All coded will be two-number codes.

Ex: 1 blink, long pause, 3 blinks with short intervals = code 13
5 blinks w/short intervals, long pause, 5 blinks w/short intervals = code 55

Code 11 is the lowest of codes and code 55 is end of codes (55 is always present)

Report back with the codes and the board will chime in on routes to take. The codes will probably get you pointed in the right direction.
 
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