TBI throttle hesitation

[bp71k5]

So I just got my new TBI motor started and have fixed the little oil and water leaks. My next issue is that it seems to idle just fine, but when I give it some throttle, it tends to hesitate and loose power and try to stall.

Two things I can think of at the moment:
1. The base timing was eyeballed I still need to do that.
2. The oxy sensor is not installed yet.

Will these two issues cause my trouble? I was going to try and drive it to the muffler shop and have them handle #2 for me but it doesn't run good enough to get there.

 

[4X4HIGH]

Start by checking the MAP sensor, make sure the vacuum hose is hooked up and not loose. You should never have to mess with the base idle screw and if you have then you must go through the process of forcing the IAC valve to fully close so that you can properly set base idle. Also you need to set base timing. Another thing is to check fuel pressure. It should be somewhere betweeb 9-13 psi from the factory.

 

[bp71k5]

Hmm, fuel pressure is something I assumed would be ok. I assume I check the pressure in the supply line and not the return?

 

[bp71k5]

Adjusting the base idle seems to have taken care of the issue. I was even able to verify the ECM is properly complaining after disconnecting the timing connector. I got my first "check engine light" on my k5 today.

It was 15 degrees retarded before which makes sense why it was running bad. I adjusted it to 4 btdc and it's tons better, but it looks like tbi is supposed to be set to 0?

Edit, I also seem to hear a slight misfire at about 2000 rpm. I assume this could be caused by my lack of oxy sensor? My clutch adjustment is the last thing preventing me from getting it to the exhaust shop.

 

[4X4HIGH]

How did you set base idle? You are supposed to jump the A and B terminals on the ALDL connector then turn the key to the run position for 30 seconds then disconnect the IAC motor next remove the jumper and start the engine and adjust base idle to proper spec. Once all done re-connect the IAC wiring. Now you can set base timing (TDC) is where it should be. This is done by disconnecting the EST wire and adjusting the timing then reconnect the EST wire. Yes, you should hasve gotten a code 42 (EST). If you pull the fuse for the ECM or remove the battery cable for 10 minutes it will clear all codes. Oygen sensor has nothing to do with a misfire if not connected. The only thing that happens without running an 02 sensor is that the ECM will not go into closed loop operation and the system will run on a pre set parameter instead.

 

[bp71k5]

How did you set base idle?

That was a typo. I meant to say I set the base "timing". If I don't have to touch any of the other IAC, TPS stuff I'll be happy. It seems to idle and run pretty well. The misfire I hear is similar to my 2001 VW. Just a subtle noise change every few seconds at random. I don't think I've ever had a car that didn't do that, but it'd be nice to make sure there's nothing wrong.

 

[Thunder]

You really need a 02 sensor to make your engine run right. 02 sensor is a vital component for proper fuel/timing management. Without an 02 sensor the ECM will default to closed loop or possibly even limp home mode and cause driveability issues.
Base timing should be set at 0*. 4* degrees is a little advanced unless you have an adjustable fuel pressure regulator and turn up the fuel pressure.
I used to run my 89 TBi at 4 degrees with 13.5- 14 psi FP for more power. But since gas went up so high I turned down the FP to 12PSI and dropped timing to 1* advance for much better fuel MPG.

 

[4X4HIGH]

Yes, i agree he needs an 02 sensor and my statement was more on the lines that he doesn't need to worry about it while he drives it to the muffler shop.

Also, without the 02 sensor the ECM stays in OPEN LOOP not closed loop. I'm sure you know this and just made a mistake.

 

[dyeager535]

Under throttle the O2 is ignored anyway, if the problem occurs with no engine load at constant RPM, then O2 can play a part, otherwise if it's as the RPM's climb under load, it's not going to matter. Since there are "partial" limp home routines, it is possible I suppose that the ECM "sees" lack of O2 input and does something to affect driveability, but not real likely.

But put an O2 sensor in there regardless.

 

[bp71k5]

Thanks, I'll be putting the O2 sensor in there. I just want to be able to drive it over to the shop without it stranding me halfway there.

 

[dyeager535]

It's only going to stop running if it loses fuel or spark. Otherwise the injection system will do whatever possible to keep it running. Still as basic as needing fuel/spark, injection simply does a better job at both than a carb.

 

[bp71k5]

I understand. It works much better now with the base timing set properly. Once I get everything hooked up, I'll see if that slight misfire is still there. The misfire is not significant enough to prevent me from driving it anywhere, but the timing problem was.