I recently replaced the exhaust manifold on my 1995 XJ 4.0, and stepped up to Bosch injectors. After getting everything put back together, the engine isn't running quite right. When it starts, at idle, everything seems fine. Accelerate a little, everything seems fine. But get past maybe 10 percent throttle and it starts to puff and putter and is down on power and just generally kind of acts like maybe not every cylinder is detonating properly, or at all.

Random facts, relevant or otherwise. It's 0°F here, both in the garage and on the road. My exhaust is currently just a straight pipe with a muffler at the end (previous owner), but I don't have a downstream sensor ('95) so that shouldn't really matter (and isn't new). I've quadruple-checked every vacuum line and electrical connection that touches the intake manifold, and checked my battery and plug wires just in case.

I'm making a list of things to check, which I can then leave here for the next person who has this problem. Do you have anything to add to the list, or anything you think I should remove?

• Check engine codes
• IAC Sensor
• MAP Sensor
• TPS Sensor
• O2 Sensor
• Fuel Injectors
  • Stethoscope test
  • Resistance of injector
  • Voltage output of injector wiring

 

Sounds like injector issue.

 

My TPS test came up negative: no dead spots across the range (although I did notice the voltage was overall low, and maxed at around 3.8; I'll definitely be putting this on my list to replace anyway when I can).

Performed a stethoscope test on the injectors - with my old antenna, which is just lying around since I have the fenders off - and I'm pretty sure I can hear all six of them ticking away. I've been hesitant to start voltage testing the injectors because I'll have to damage insulation to do it; waiting until I've tested everything else.

Disconnected my O2 sensor to see if that would change anything: it didn't, so the O2 sensor is probably not the problem (but I have a replacement ready that I'll install when I replace the down pipe).

 

Check fuel pressure for drop outs from a leaking injector O ring.
Verify you connected each injector to the proper wiring connector.

 

Probably going to need to buy that fuel pressure gauge I've been looking for an excuse to buy, aren't I?

 

did you reset the computer after replacing the injectors? i've read it's a good idea to do so. i'm getting ready to do the same work on my jeep but I was thinking of doing the manifold first, see how it runs, and if everything is fine then do the injectors. might be a little longer but at least you know where to look at if something funky happens like in your case.

you could try putting the old injectors back, see if it changes anything

 

3.8V is normal max for the TPS. Should show 100% in a scanner. Higher than that will trigger a high voltage code in the PCM

 

Happy new year Salid, nice to see you back! 327...I know you checked but still. I think your MAP is still on the firewall with that brittle little tube from the TB. Swapping injectors it's common for that to get boogered. Any crack , leak, or blockage is not good. Unlikely with your symptoms, but so easy to double check. Best of luck, and do please post back after you get it.

For fun you might try floorboarding it and see what it does. There it will ignore most sensors and run on defaults. Me proposes that if it does launch like a rocket, fuel pressure likely is not the issue.

 

Hey Don, been here a while Getting more active in OEM Tech threads in between splitting firewood

 

Did see yer head poking up alittle. Same here, didn't cut enough wood last summer. Nice to have besides the DD Jeep, a thrasher, and an extra as well

 

And fixed! freegdr wins the prize: injector issue. I purchased some Bosch 0280155703s but received 0280155746s, and in my rush to install them didn't double-check. I put my old Ford injectors back in, and everything's 100 percent.

Thanks to everyone!

 

Thinks that would be an installer issue.

 

Much thanks foe getting back. That bad response with throttle has been said to be maybe a lean condition, & the 746 do have a lower flow rate. You should be able to resell those to someone with an 87-90 Renix Jeep. Glad you got it!