I'm sure problems like this have been discussed before, but I've checked the previous threads and haven't found a solution yet. Hoping for some advice.
I've got an '89 Ramcharger with the 318, that will start and idle without much trouble. One cylinder misses every once in a while but nothing major or unexpected given the age. I'd say it idles pretty smooth all told.
As soon as I push the accelerator any at all, it immediately falls flat, choking and stumbling and almost dying but usually not actually doing so. The RPM drops and it sounds like it's running on about half or less of the cylinders. It will continue running this way as long as you hold your foot in that position, it never improves or changes once it starts missing that way as long as you don't move your foot. This happens in Park, Neutral, and also while driving -- so I don't drive it anymore, I don't need it dying in traffic.
If you take your foot off and let it idle it generally comes back about like it was before. If you go on and accelerate harder, it quits choking and dying and starts running -- but not quite as smoothly, it still seems pretty rough and like it could be missing part of the time.
There are several signs that it's running rich. The exhaust smells heavy and gassy, the fuel mileage has dropped from terrible to unbelievable, and the only code in the computer besides 12, 37, and 55 (all of which can be ignored) is 52 which seems to be an O2 sensor reporting a rich condition (but I know that doesn't mean the O2 sensor is bad, just that the reading is out of spec possibly due to something else.)
The ignition components (wires, plugs, coil, cap, rotor) were changed recently enough to feel confident in them, and last time I checked the fuel pressure I saw nothing concerning.
Because the problem seemed related to throttle position rather than any load characteristics on the engine, I figured throttle position sensor was the most likely issue, I figured it probably had a dead spot in it that was not making contact and thus not giving the off-idle fuel that was needed, so I just installed a new one tonight; made zero difference.
Almost all the threads say to use a timing light and look at the fuel injector pattern. I hooked up the timing light but I can't see anything I'd describe as a cone, a spray, or any pattern at all looking down into the throttle body under the two dome-shaped things that I think are the injectors. I do see some liquid fuel sloughing down the back wall of the throttle body chamber in a fairly even cascade, but I can't spot any fuel vapor in the "air" between the injector and the air intake flaps. Most threads say check it with the timing light but don't say any more specifically how, and this is not a light that has any sort of adjustment on it so if the problem is I'm not timed in sync with the fuel, I don't believe I've got any way with the tool I have to adjust that way. I'm putting the pickup on the #1 plug (front driver's side.)
Other than the fact that the TPS was the most likely suspect and made no difference, and that the fuel dripping down the back wall of the throttle body might suggest that the injectors are shot, I don't quite know what to check next or how. I gather 02 sensors require a scope to verify they're sending the proper signal, it's nothing you can check with a multimeter... I own a bench scope but not an automotive one and I'm not sure I can easily tote the electronics one outside to the truck or if it would even give the necessary information when I got done.
I appreciate any suggestions. I'll try to carry them out but I may have to ask follow up questions to figure out how to do so. A lot of the threads where issues like this have been discussed went over my head in a hurry. I've got enough parts swapping and maintenance experience to get a lot of things done, but not so much on the diagnostic side, especially where TBI is concerned.
I've got an '89 Ramcharger with the 318, that will start and idle without much trouble. One cylinder misses every once in a while but nothing major or unexpected given the age. I'd say it idles pretty smooth all told.
As soon as I push the accelerator any at all, it immediately falls flat, choking and stumbling and almost dying but usually not actually doing so. The RPM drops and it sounds like it's running on about half or less of the cylinders. It will continue running this way as long as you hold your foot in that position, it never improves or changes once it starts missing that way as long as you don't move your foot. This happens in Park, Neutral, and also while driving -- so I don't drive it anymore, I don't need it dying in traffic.
If you take your foot off and let it idle it generally comes back about like it was before. If you go on and accelerate harder, it quits choking and dying and starts running -- but not quite as smoothly, it still seems pretty rough and like it could be missing part of the time.
There are several signs that it's running rich. The exhaust smells heavy and gassy, the fuel mileage has dropped from terrible to unbelievable, and the only code in the computer besides 12, 37, and 55 (all of which can be ignored) is 52 which seems to be an O2 sensor reporting a rich condition (but I know that doesn't mean the O2 sensor is bad, just that the reading is out of spec possibly due to something else.)
The ignition components (wires, plugs, coil, cap, rotor) were changed recently enough to feel confident in them, and last time I checked the fuel pressure I saw nothing concerning.
Because the problem seemed related to throttle position rather than any load characteristics on the engine, I figured throttle position sensor was the most likely issue, I figured it probably had a dead spot in it that was not making contact and thus not giving the off-idle fuel that was needed, so I just installed a new one tonight; made zero difference.
Almost all the threads say to use a timing light and look at the fuel injector pattern. I hooked up the timing light but I can't see anything I'd describe as a cone, a spray, or any pattern at all looking down into the throttle body under the two dome-shaped things that I think are the injectors. I do see some liquid fuel sloughing down the back wall of the throttle body chamber in a fairly even cascade, but I can't spot any fuel vapor in the "air" between the injector and the air intake flaps. Most threads say check it with the timing light but don't say any more specifically how, and this is not a light that has any sort of adjustment on it so if the problem is I'm not timed in sync with the fuel, I don't believe I've got any way with the tool I have to adjust that way. I'm putting the pickup on the #1 plug (front driver's side.)
Other than the fact that the TPS was the most likely suspect and made no difference, and that the fuel dripping down the back wall of the throttle body might suggest that the injectors are shot, I don't quite know what to check next or how. I gather 02 sensors require a scope to verify they're sending the proper signal, it's nothing you can check with a multimeter... I own a bench scope but not an automotive one and I'm not sure I can easily tote the electronics one outside to the truck or if it would even give the necessary information when I got done.
I appreciate any suggestions. I'll try to carry them out but I may have to ask follow up questions to figure out how to do so. A lot of the threads where issues like this have been discussed went over my head in a hurry. I've got enough parts swapping and maintenance experience to get a lot of things done, but not so much on the diagnostic side, especially where TBI is concerned.
Yes, I pulled the codes by cycling the ignition three times and counting flashes; I mentioned them in my original post:
, disassemble fuel pump module assembly just to the point of being able to remove the fuel supply hose from the fuel pump module lid (Figure 1).
