Fuel System Puzzle

[LowSHO]

I'm a relatively inexperienced mechanic. My 91MTX was exhibiting symptoms of fuel starvation, intermittent stalling and hard starting.

I ran my codes: 87 and 96 koeo, 87 stored (couldn't run koer)which pointed to the fuel pump. So I went to this forum for instructions to test the fuel system and the fuel pump would not cycle long enough to take a reading (it would stay on less than half a second).

So I replaced the fuel pump, and the filter while I was under there.

The symptoms persisted, although the new Walbro 190lph would run "normally" at startup. Fuel pressure test results as follows:

With the FP test point grounded, I got 32 lbs static pressure - however, the fuel pump would not run continuously, only for a couple of seconds, then shut off.

I reset and tried again. In relieving the meter, I got very little gas and a lot of air, I thought perhaps there is air in the fuel lines from the pump change (although the pump should take care of that, I believe)

Priming the system several times until I got only fuel from the pressure discharge, and then priming the pump 3 times, I got 38 lbs static.

I then tried a single prime on static (still with the FP test point jumped) and only got 32 lbs.

In each case I waited 3-5 minutes for the leakdown, and in each case there was no change at all in pressure.

I then did the engine on test, got a solid 40 lbs, with virtually no change across a range of engine speeds (FPR plugged, FP test point not grounded).

What should the FP be doing when the test point is jumped - running continuously or running up to designed pressure? Mine gets up to the right pressure, but shuts off.

That air in the system bothers me, anyone have any idea why it was there?

My koer codes were 25 and 73. There was no pinging, so I ignored the 25, and I thought I goosed the engine well enough to void the 73.

I had replaced the ICRM (containing the fuel pump relay) earlier. I can hear the click and the fuel pump when I turn the key on.

Advice is greatly appreciated.

 

[projectSHO89]

With the FP test point grounded, the FP should run constantly.

The air should be purged out of the system over time (and not much of it).

BTW, what is your current situation? Does the car still exhibit the original symptoms?

Other than the short "on" time of the pump relay, your system sounds almost, but not quite, normal.

Steve

 

[LowSHO]

Before I began these repairs, I was stranded twice, and had to have the car towed (same tow truck driver in both cases. It led to much hilarity on his part). So I am trying to clear all this up before I go out on the road again.

I am going to test the fuel pressure again this morning to see if I still have good pressure, or if air has entered the system again (I still don't see how that happened).

Since the FP should run constantly, I'm now not sure I'm testing it properly - I'm running a jump from the FP test point to the same single plug that I use to run the codes. Is that correct?

 

[projectSHO89]

LowSHO:
Since the FP should run constantly, I'm now not sure I'm testing it properly - I'm running a jump from the FP test point to the same single plug that I use to run the codes. Is that correct?

No. You should be connecting the FP TEST pin to GROUND . The single plug is the STI (SELF TEST INPUT)

Steve

 

[sdpatt]

Those codes point more towards the power supply for the fuel pump rather than the pump itself. The integrated control module (ICM) under the driver side of the plastic cover above the radiator contains the fuel pump relay and may have either intermittent operation of the relay or a bad connection to of from the box. Verify contant power to the ICM input and constant output from the boax to the fuel pump. The wiring from this box to the pump should also be verified for continuity. There is an intermittent power supply to the pump - somewhere.

 

[LowSHO]

Ah! Intermittent electrical gremlins. More fun than a week at the beach. I'll report back later.

Thanks.

 

[LowSHO]

Well, as I began to try to track down these gremlins, the first thing that I came up with was the part number for the CCRM, which had been replaced a month ago, by a repair shop. The one they put in my car was for a Gen III!

So I ordered the proper part and installed it. Car started and ran fine. I performed the idle reset procedure, then ran the codes. I got 11's across the board. So I figure the problem is solved. Not so.

After the first successful half-hour or so run, the car will now start maybe sometimes, then only run for 5 minutes (almost exactly) and stall.

In addition, when I turn the key on, I can hear the fuel pump, but also the ETAC blower (the display reads "OFF").

I ran the codes, KOEO only, and got 11's again, so the system didn't even record the stall.

At the same time, the digital display for the radio read "- - -" as if it didn't have enough power. So I checked the battery and alternator, and they were fine (as far as I could tell).

Out of frustration, I started to crank the engine hoping it would catch. Just as the battery seemed to have had enough, the engine caught, the blower turned off when I pushed the OFF button, and the radio operated normally. The car ran for almost exactly five minutes and stalled.

There's no gasoline smell, the fuel pressure tests out fine, the pump was recently replaced.

Could this be a bad CCRM (new from Autozone)? Or am I missing something else entirely?