Stumble at start + horrible gas mileage.

[joshuatyler1]

Alright. I'll begin this with a preface that I've probably read every post on every forum about anything Volvo. Still...I can't seem to rid myself of this problem.

1999 V70XC with 119,000 miles. It's my wife's care & she uses it to run a small business walking dogs. Recently replaced fuel pressure regulator, fuel filter, air filter, plugs, MAF sensor, all to no avail. Here's the jist:

Car runs fine & starts fine right in the morning. If you start it, turn it off, then start it again, no problems. If you drive to the store, shop for 20 minutes, come out & start it, it will stumble on start up & most often die. Try again & it starts like nothing ever happened.

Apart from the starting issue, the car runs very well. Gas mileage is VERY POOR (<15mpg). Yesterday, while my wife was driving, the CEL came on & the code read P1171. (This code is what prompted the MAF replacement). I've read the many posts on the P1171 code of death. What should I do next? Change 02 sensors? (how the *#&$ do you get to the front one?) How do I check for vacuum leaks?

Thanks for the help in advance.

Other relevant info: No leaky injectors, no black smoke from exhaust, fuel pressure good.

[redoak]

I cant't speak to the starting and stumbling, but I did experience s sudden and precipitous drop in fuel mileage and the CEL light came on eventually. The code suggested the MAF sensor. That was replaced as well as the O2 sensor. Neither fixed the problem. In researching the symptoms on line, I found a reference to a Honda (I think) recall to replace the fuel rail damper. Thought it was worth a try for my '98 V70 XC. Volvo calls this part a pulse damper. Low and behold, that was the problem.
I hope this helps.

[mesaAZ2000XC]

The front O2 is the easiest one to get to...three bolts from the heat shield, slide it out of place, and there she sits.

[joshuatyler1]

Thanks for the replies. I looked at getting a damper when I changed the pressure regulator. Nice to know it solved your problem. I'll give it a shot.

I'll give a stab at the front 02 sensor tomorrow morning. I'll let you know how it goes.

[joshuatyler1]

So, I was on the last bolt on the heat shield and I busted my ratchet's adapter. Sadly, the 02 sensor will wait until Monday. I did however replace the "fuel pressure damper/absorber." No change.

I also wanted to add that I've replaced the "antenna ring/immobilizer" as I learned on these forums that it can also often cause a stumble at start.

I'm getting to the end of my rope. I pulled apart the whole air intake & checked for leaks. (Haven't gotten to the ETM. I seems so far back there & I just haven't had the time to get to it).

Any suggestions anyone? Why am I getting such bad mpg? (<15mpg) Why the stumble at start?


Update: The CEL went off today. Don't know if that means anything. Poor mileage & stumble on start after driving (~20 min) remains.

[JRL]

What's the code?
Don't say a CEL went on, tell us the CODE

[joshuatyler1]

Thanks for the response. Check previous post. Same code. P1171.

I decided to check my fuel pressure again today & lo & behold.

Fuel pressure with key turned on: 0 psi.
Cycle from on/off multiple times: 0 psi.
(The needle doesn't even move when I flick the key on and off.)
Try to start - car stumbles and almost catches.
2nd try to start - car fires up & pressure slowly climbs from ~10 psi till it finally settles at 44 psi.
Rev the engine: 44 psi.
Turn off the engine: pressure drops immediately to around 6 or 7 psi.

Diagnosis?

I'm scared to say fuel pump. Could it just be the check valve? I've heard of people installing an inline check valve.

Any other ideas? I really appreciate the help guys. I love this forum.

(Side note. I may be the only american volvo owner on this forum who speaks fluent Swedish.)

[knucklebuster]

I've got a thread running on intake leaks, which I have been looking for on my car and not found.

In trying to solve this I talked to my mechanic many times, as well as paying him several times. He once had a car do this due to an intermittently faulty fuel pump relay. Your post makes me want to look into fuel pressure more thoroughly. good luck.

[joshuatyler1]

So, I added and inline fuel pressure check valve & my deteriorating fuel pressure has disappeared. That's right. No more hard starting after driving! No stumble on start. Best thing ever. Cheap & easy to install.

1 problem still. Check engine light with P1171 is still on & I've got an 02 sensor I'm going to try and put in next week. Hopefully it will end my woes. Gas mileage still remains dismally low. ~15 mpg.

But at least I have a Volvo that starts up on the first crank & maintains fuel pressure. I love it!

[knucklebuster]

these cars seem to take time to bounce back and if the O2 sensor is fouled due to the other problem it will affect running. May resolve in time. They are supposed to last about 60k miles according to Bosch.