Check engine light no code

[dana0330]

I am getting a check engine light when driving down the highway and when I check for codes I get a 55 no faults. Also the car hesitates at times. I will check the airflow sensor. I have new knock sensors and injectors I replaced them when I had the plenum off. The trans seems to shift a little late when it hesitates.

[Q45tech]

Swap in your spare [ for diagnostic purposes] ecu or use a Consult II to delve deeper than the simple internal flashing light method.

Usually we find sluggish [not totally failed] O2 sensors as the culprit.
Also examine the 2 different pulse outputs from CAS as age and wear [dirt] can sometimes cause unstable or dropped 1 degree signals.
ECU senses something not perfect but just not a TOTAL failure of sensor signals.

[goody90q45]

I am getting a check engine light when driving down the highway and when I check for codes I get a 55 no faults......

Don't feel bad. You're not the first one with a CEL to get a code 55. It's all in the sequence and leaving the adjusting screw in the right position the last time codes were read.

If you're getting a CEL then there has to be stored codes. For starters you need to make sure the screw in the back of the ECU is in the full CCW position and the red light is on and not blinking.

With the key in the ON position, the ECU's red light on, and the screw in the full CCW position, turn the screw fully CW, then fully CCW to read the codes. When you're done, turn the screw fully CW, then fully CCW to get a solid red light again.

If you've found the screw in the wrong position or it wasn't reset properly the last go-around you may need to complete this sequence, go out for a drive until the CEL comes on, and then pull the codes. Leave the ECU connected and laying in the floorboard until you get through your engine issues. Your ribs will thank you. Good luck.

[dana0330]

I got a used airflow sensor and the hesitation is gone but the engine light is still comming on when going down the highway. I may put in 2 new O2 sensors I had one melted cat and I think they are the orignal ones. The car is running a bit rich. Also do the throttle position sensors go bad?

[dana0330]

The car was running good last night and in the morning, went to go out and pick up som parts an it started bogging again. It boggs around 1500-2000 lacks power up hills. I went inside the store came back out and drove back with no problems. I have never seen a car cause a intermittent bogg.

[Q451990]

Might be worth monitoring your fuel pressure. You could have one of the three modes on your FPCU coming and going intermittently.

Heath

[dana0330]

I checked the fuel pressure it seems to be ok the car ran great in the morning but started to bog out in the afternoon. The fuel pump module has never been out of the car, and I tryed grounding the fuel pump and I could hear it get loud and the fuel pressure went up but it still would bogg. I did notice that when I floored it the gauge did not go up. I have seen pumps go that had good pressure but low volume does anyone know if that hapens to these pumps? I am tired of this intermittent bog I can't drive the car.

[goody90q45]

Were you able to pull ECU codes? Bad O2 sensors wouldn't cause a noticable bog, only high fuel consumption and a noticable drain on your wallet.

[dana0330]

No I could not pull codes I culd replace the O2s I do not think they have ever been replaced.

[goody90q45]

Still got a CEL? Without pulling codes all we can do is guess and you'll be throwing $$ at parts. If you want to send me an email I can talk you through it on the phone.

[Infinitiguy19]

You need to replace the fuel pump with a brand new one.

If its not 34 PSI at idle and 43 PSI at Wide Open Throttle, then you might need a new fuel pump and a good Fuel Pump Control Unit.

[dana0330]

I did get a code finally code 34 for knock sensor checked the sensors one is 550k ohms and the other is 875k ohms. I replaced the sensors when I pulled the plenumn but not the harness. I ordered a harness I read some info on this sight about knock sensors causing the same problem that I am having. Does anyone know if it is possible to replace the harness without having to pull the plenumn?

[goody90q45]

I did get a code finally code 34 for knock sensor checked the sensors one is 550k ohms and the other is 875k ohms.......

Progress!! Good to see you were able to pull ECU codes. But...the KS code by itself does not light up the CEL and in the 90-95 Q one dead or dying KS will not affect acceleration at all. The 96+ Q's (OBD2) seem to be a lot more sensitive to a dead KS. I drove my 94Q for 4 years with one dead KS and it always accelerated like a rocket.

Are you still getting a CEL? I suspect not if the only code is 34. If no CEL you need to take another look at the fuel pump, FPCU and fuel filter. If you do see the CEL light up, pull the codes because there will be more than just code 34 stored. Is it idling smooth? Did you ohm test the fuel injectors when you ohmed the KS and what were the results? One dead or plugged injector may not light the CEL or affect acceleration that much but the car will be shaking at idle. Ditto for O2 sensors not functioning 100%- poor gas mileage and maybe no CEL in the early stages but the car shouldn't bog down as much as you describe.

.... Does anyone know if it is possible to replace the harness without having to pull the plenum?

It's possible on the 97+ Q. If you weigh 80 pounds or less dripping wet (Naladude?) your hands might be small enough to reach between plenum runners to reach the connectors but it's doubtful. IMHO you'd have to at least loosen the plenum and raise it a few inches to get access. If you're getting the KS readings at the harness connector then I wouldn't think there's a problem with the harness. I'd put this repair on hold.

[qship96]

Just to clarify on the 96 OBD2 equipped Q, bad knock sensors do not cause any driveability issues and very little change to overall acceleration.....after replacing mine, the biggest difference I felt was slightly better "tip in" response to the accelerator.....maybe 10-20 horsepower difference?????

[Infinitiguy19]

Qsiguy (Guy with the red Turbo Q) saw a 40 Horse Power loss on the dyno due to bad Knock Sensors.

[dana0330]

The car idles great I replaced the injectors when I had the plenum off (they were the reason the plenum came off). I know on most other cars I have worked on if they have bad knock sensors they retard the timing way down causing the car to lack power. I am getting the code 34 and a code for a exhaust temp sensor one of the coputers I am using is a California emmisions one but the car runs the same with both computers. I have good fuel pressure but the pump module has never been replaced I pulled one out of a car from a junkyard it was a replacement I know because the plastic on the connector end was burned and the module is not I will put the replacement one in anyway. I am going to have some time to work on the car in the am but do not know If I will finish it.

[goody90q45]

......I am getting the code 34 and a code for a exhaust temp sensor. one of the computers I am using is a California emmisions one but the car runs the same with both computers........

With those codes the CEL should only come on when you're running the CA emissions ECU because of the EGR exhaust temp sensor not being installed on your Fed emissions engine. It's normally on the plenum at the base of the EGR valve. The EGR valve doesn't operate until after about 20 minutes of driving. Is this the bog you're feeling? I'm not sure but could the CA ECU be the problem?

....... I have good fuel pressure but the pump module has never been replaced I pulled one out of a car from a junkyard it was a replacement I know because the plastic on the connector end was burned and the module is not I will put the replacement one in anyway. I am going to have some time to work on the car in the am but do not know If I will finish it.

You can quickly install a replacement FPCU for test only purposes by reaching in through the trunk trim and unpluging the FPCU connector. Plug it into the replacement FPCU, run a jumper from the FPCU body to ground, and let it dangle in the trunk while you do a test drive. No need to pull the back seats.

Does the FPCU or its connector in your Q show signs of overheating?

[dana0330]

The car runs the same with both ecms my fuel pump control module looks ok it has never been replaced. The bog dose not happen all the time and it is not temp related.

[dana0330]

I spent some time on the car today put in 2 new o2s put in the used fuel pump control module and took the car for a drive it ran good for a short time and then lost power started to run rough and smoke reall bad, and was hard to start. there was a lot of liquid comming from the exhaust from the drives side. I was able to narrow it down to the drivers side of the engine. I removed the spark plugs and foyd the second cylinder full of gas. I have to take the plenum off so I will have to remove the injector. I replaced all 8 mabey the seal is leaking. This car is a big pain in the butt.

[Q45tech]

Not as big a but pain as the same year Mercedes V8 or BMW or Audi or Bentley V8 much much less difficult than the Lexus V8 with plug wires and a starter under the plenum.

[qship96]

Qsiguy (Guy with the red Turbo Q) saw a 40 Horse Power loss on the dyno due to bad Knock Sensors.

Was his car in 100% stock tune when this test was done? You cant compare numbers if he had already modified the engine.

[elwesso]

Yeah you definitely have a bad injector seal... You're going to need to check that out, be sure to lube them up real good when you put them in. Ive had good luck with vaseline on the o ring and the inside bore of the fuel rail.. you should press down on them with your thumb, you will feel them seat down all the way.. If you use the cap to screw them down, it will surely go in crooked and cause this issue..

What were your fuel pressure readings? If your FP is quiet, I might not suspect it.. Usually FPCU (read USUALLY) are either good or bad, they usually dont cause weird driveability issues...

The EGR temp sensor code is exactly what you said, for cars with california emissions... and if you have a 92, it did not have an EGR temp sensor unless it was a cali model...

Also o2 sensors can only affect things ~20% either way, so you wouldnt see a HUGE decrease in gas mileage because the fuel trim is only allowed in a narrow range..

Im leaning toward a MAF issue, you said you replaced with a used one?

[elwesso]

Qsiguy (Guy with the red Turbo Q) saw a 40 Horse Power loss on the dyno due to bad Knock Sensors.

Was his car in 100% stock tune when this test was done? You cant compare numbers if he had already modified the engine.

Food for thought, but 30-40 HP is not night and day! Thats about what an ECU will do, and its not night and day but it still makes a difference. I would say qualitatively thats a pretty good estimate...

And Paul is correct, according to what I remember Shane dynoed his car before/after KS without other mods...

But you're still right, on a G50 KS alone dont cause major driveability issues, just down on power a little bit...

[Infinitiguy19]

Regardless of what else you do I'd definitely test the knock sensors. I actually had my car on a dyno with a bad knock sensor and it was down 70-80 hp from normal just from a bad knock sensor. You'll feel that on those hills for sure.

[Q45tech]

Chassis Dynos don't test from idle thru 3,000 rpm [usually] so the only lost 30 HP is a misnomer. At 2500 rpm the engine is only putting out ~ 120 HP so 30 is pretty significant from bad knock sensors.

Best to stopwatch 0>60 acceleration against the 7.2>8.0 seconds STAMDARD where a bad KS can add a few seconds.

[dana0330]

I am going to replace the knock sensor harness while I have the plenum off to repair the injector. I have always used motor oil when I put injectors in I found it to be the best, I did not use the caps to seat the injectors it may have just torn or something I will know when I pull it out.

[dana0330]

Pulled the injector yesterday the seal is ok found the injector stuck open. Put power and ground to it and it was not clicking. Tryed it again today and it is not open and it clicks when putting power to it I guess that I found my intermittent problem, I ordered a new injector Just in time I put them in last July but did not put the car on the road untill last month. The warntee is for one year I will cross my fingers and hope the others are ok. Befor any one asks I put in rebuilt injectors.

[Q45tech]

No such thing as a rebuilt injector only used cleaned up junkyard pulls called remans/rebuilds.

If only a vehicle had a method to lock owners in stocks [on the town square] and persuade people to throw rotten tomatoes for 24 hours, while they rethink mainteances and repairs.

To punish them for vehicular abuse.

[dana0330]

I am a mecanic I have my own shop and I have put rebuilt injectors with out any problems. A cleaned up injector should be ok injectors do not go that often I have done a few but I my over 20 years working on cars I have only done a hand full.

[CCUBS1]

I have the exact same problem the CEL only comes on between 45-55 mph i can drive all day at 60-75 or 40 and under and it never comes on but 1 min at 48 and pop but then when i turn the car off it goes away so when i test i get a code 55 over and over. I know my #8 injector is bad so I'm hoping that is my problem the only other issues i have that i know about is my tcs/slip lights are on (haven't tested the relays yet), and my ac only works on high and blows warm at idle hoping replacing the resistor will fix both of those. The car bogs going up hills some days and has slow take off sometimes but, as with yours, even knowing that my injector is not working some days it drives fine but with the miss and some days it's like a shopping cart with a bad wheel just rough as hell. I'll be glad when yours is fixed so i know what i need to do lol.