I have a 1998 Trooper with 70K miles. The Check Eng Light has been throwing 1171 errors (lean condidtion during exceleration). One of the trouble shooting recommendations is to test fuel pump pressure. Shop manual says it should be 44-52 psi. I tested the pressure on the fuel injector rail and the pressure reads 38psi with the ignition on. With the engine running it reads between 35-38 psi. I also tested the pressure by the fuel filter with same results.

Seems like I need a new fuel pump but before I spend $300 on a new one I wanted to see if others agree? Is this typical for a Trooper to need a new fuel pump at 70K miles?

Also, any opinions on after market pumps ($100) vs OEM for $300?

Thanks.

Before you spend that kind of money, make sure that there isn't a restriction of some sort in the line from the tank to the engine.

A good starting point would be to swap your fuel filter. If it is clogged it could be causing a drop in your pressure.

Thanks for the suggestion. I did replace the fuel filter yesterday (the old one seemed OK also) before I read the pressure.

I responded to Mike privately, but here are a few more thoughts.

I think this may be the beginnings of a bad IMG. But...I am not 100% sure on that. The codes thrown are not for bad O2 sensors, they just indicate low voltage (a response to the lean condition IIRC). The other code P1171, indicates a lean condition in the fuel system under acceleration. I am not sure how the computer decides this. It should be through the 02 sensors, but...???

I guess it could be the fuel pump. The spec in my Chiltons indicates 41-46 as the fuel pressure. 38psi is not that far off and I cannot imagine it being the cause of the lean condition.

Other suggestions in the past have been to clean the MAF. I would suggest doing this. I would also consider pulling off the EGR valve and cleaning it too. If for some reason it is sticking, maybe it is causing a vacuum leak. Again, that is just a wild ass guess.

Good Luck,
Michael

A lot of Troopers have had bad fuel pressure regulators, too.

Thanks for everyone's response. I have already cleaned the EGR and the MAF and they did not help. I've explored a bad MF gasket and will check this out again. I'm also going to try a new fuel pressure regulator as suggested (a lot cheaper than a pump). Thanks for all the help.

I thought I'd give an update on my 1998 Trooper check eng error codes (P1171, P0137, P0157). These all have to do with the engine running "lean" during hard excelleration. The P0137 is one of the rear O2 sensors reading lean and the P0157 is the other side rear O2 sensor reading lean.

Here is what I have done so far:

1)Replaced fuel filter (cheap)

2)Check fuel pressure (on rail) and reading 33 to 38 psi (book say it should be 44 to 52)

3)Replaced Fuel Pressure Reg. (now reading 38 psi at idle and 42 with pump turned on but engine not running) Not sure why pressure is not within spec...any thoughts?

4)Checked fuel pressure (on rail) with return hose squeezed off with plyers. PSI goes up past 60 right away....seem fuel pump is not the problem.

5)Replaced rear O2 sensors (both sides)

6)Replaced Intake Manifold Gaskets (old ones "looked" fine).

After each repair I've cleared the CE codes and taken it for a spin and when I stomp on the gas imediately the CE light come on and gives the same codes. I noticed one of the fuel injectors sucking air (I suspect this is from disturbing them while changing the IMF gaskets). I've order a new O rings/seals and will replace these tomorrow. After that I've run out of things to try.

Any suggestions from out there or is it time to admit defeat and bring it to the dealer?

Thanks

Mike

My take is that you truly have a low fuel pressure condition. All the codes point towards this. All but one fuel pressure check says this. The one check that shows an adequate pressure is with the return line pinched off. That is a classic symptom of a partially failed pump (i.e. good pressure but only at a very low flow rate).

You don't seem to be reporting a problem during normal acceleration. Therefore one option is to lose the lead foot, live with it (i.e. no symptoms in normal driving) and hope it doesn't get worse.

Alternatively, you can continue tracing the problem back to the tank (e.g. bad pump? or clogged pump screen?).

My suggestion is to first try yet another new fuel filter. You wouldn't be the first person to get such a bad batch of gas that it takes more than one filter to trap out the junk. Granted in today's EPA controlled world gas contamination in storage is a relatively rare event. However for the price of a filter and a little labor this just seems like a good next step. When you do be sure to inspect the removed filter for junk. I normally just stand mine in a cup and look for particles to drain back out. If you find nothing then you have wasted a little time and now have a good trail spare. If you find a bunch of junk you may have found your problem.

Just my hopefully helpful $.02.

Latest Update: I replaced the fuel pump and screen. I also replaced the filter again. Fuel pressure on the rail still reads around 38 psi at idle vs spec of 44 to 48. When I disconnect the vacuum hose on the pressure regulator the pressure goes up to 50 psi. The regulator is new. Is it possible I have a bad regulator OR is it possible that too much vacuum pressure is being applied to the regulator? Anyone have any thoughts on this? The CE light comes on durring hard acceleration although it happens less often than before. Thanks

Given all the work you have done I sure would like to think you truly have the correct fuel pressure. Isn't the spec 41-46psi, or am I reading the wrong section of the Helms manual. Or maybe 98 has a different spec than in my 99 manual. If not, 38 is not that far from 41psi and well within a possible gauge error.

What have you done to check for an individual injector problem? Could it be you have a partial plug in one that is causing the problem?

Per the manual water and or alcohol in the fuel can also cause your codes. Presumably a water problem would have gone away by now. Any chance that fuel in your area went to a very high alcohol content for the winter? If so you might try a different brand or some from an outlying area. Granted this is grasping at straws but then again it won't cost you much to try some different gas.

Good luck.