skipc
NAXJA Forum User
- Location
- Georgia & points west and south
I've got a strange problem with my 89 XJ 4.0:
About a hundred miles into a tank of gas it started stumbling/surging at idle and at cruising speed, but not during hard acceleration or at idle in neutral. At first I thought it was bad gas (we've had a lot of rain lately, and who knows when the tanker filled the ground tanks at the station...). It doesn't happen 100% of the time, about 50%.
I ran Berrymans, Sea Foam, and then ethanol at max concentrations, but nothing helped. I then drained the tank through the fuel rail (until air was found). The gas didn't seem to have water in it (clear container test), but maybe it was just "bad", even thought it was BP. I put in another major brand. It still does the same thing.
It stumbles on light accel, idle in drive, and cruising at highway speeds. WOT, hard accel, and decel seems fine. I disconnected the O2 sensor to force it into open loop mode, but no diff. The fuel pump pumps fine, and I disconnected the vacuum line to increase the pressure to test. No diff. If it were pressure or delivery, then I should get bad performance on WOT, but I get just the opposite...
It starts fine, and I keep it running at idle by using my foot when needed. I had long since manually adjusted the idle stepper to manually override idle speed. Rock solid until now. Something has gone wrong, and of course it happens at cruising highway speed too, so it isn't an idle circuit issue.
Any ideas what it could be? It's intermittent, so it's tough to be under the hood to find at the same time. I think I've ruled out gas, and it seems to be opposite a fuel delivery problem. It could be an ignition problem, but any pointers on why I have it only some time, and only at light usage, not WOT or heavy accel?
Thanks in advance,
Skip
About a hundred miles into a tank of gas it started stumbling/surging at idle and at cruising speed, but not during hard acceleration or at idle in neutral. At first I thought it was bad gas (we've had a lot of rain lately, and who knows when the tanker filled the ground tanks at the station...). It doesn't happen 100% of the time, about 50%.
I ran Berrymans, Sea Foam, and then ethanol at max concentrations, but nothing helped. I then drained the tank through the fuel rail (until air was found). The gas didn't seem to have water in it (clear container test), but maybe it was just "bad", even thought it was BP. I put in another major brand. It still does the same thing.
It stumbles on light accel, idle in drive, and cruising at highway speeds. WOT, hard accel, and decel seems fine. I disconnected the O2 sensor to force it into open loop mode, but no diff. The fuel pump pumps fine, and I disconnected the vacuum line to increase the pressure to test. No diff. If it were pressure or delivery, then I should get bad performance on WOT, but I get just the opposite...
It starts fine, and I keep it running at idle by using my foot when needed. I had long since manually adjusted the idle stepper to manually override idle speed. Rock solid until now. Something has gone wrong, and of course it happens at cruising highway speed too, so it isn't an idle circuit issue.
Any ideas what it could be? It's intermittent, so it's tough to be under the hood to find at the same time. I think I've ruled out gas, and it seems to be opposite a fuel delivery problem. It could be an ignition problem, but any pointers on why I have it only some time, and only at light usage, not WOT or heavy accel?
Thanks in advance,
Skip