G3.Spiffy Posted June 7, 2020 Share Posted June 7, 2020 I’m finishing up the last few things on my EA82 SPFI swap (1986 GL 5MT) and am noticing a stutter at idle when the car is parked with the trans in Neutral and the brake pedal pressed and released. Initially I thought this was a vacuum leak, so I checked to make sure I have the booster hose on in the right direction, which it is, and that it holds vacuum, which I believe it does because I disconnected the hose after turning the engine off and it made a suction sound as if it was negatively pressurized. This only occurs when the brake pedal is pumped at idle, it’s not there if you rev the engine up a bit and then pump the pedal. The car runs fine otherwise. Any help or links to useful threads are appreciated! Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted June 7, 2020 Share Posted June 7, 2020 electrical power demand also increases as the brake lights come on - maybe pull their fuse or their bulbs to troubleshoot that idea? Link to comment Share on other sites More sharing options...
el_freddo Posted June 7, 2020 Share Posted June 7, 2020 It’s possibly the idle mechanism’s slow reaction to a change in vacuum. Otherwise to me, it points to a secondary vacuum leak that the SPFI system is able to deal with, and a brake booster issue. My initial thought was brake booster. Best to get a vacuum pump and give it a thorough test. Cheers Bennie Link to comment Share on other sites More sharing options...
G3.Spiffy Posted June 8, 2020 Author Share Posted June 8, 2020 2 hours ago, 1 Lucky Texan said: electrical power demand also increases as the brake lights come on - maybe pull their fuse or their bulbs to troubleshoot that idea? This isn’t my issue because it doesn’t continue to stutter while the pedal is pressed, just when pumping it. 1 hour ago, el_freddo said: It’s possibly the idle mechanism’s slow reaction to a change in vacuum. Otherwise to me, it points to a secondary vacuum leak that the SPFI system is able to deal with, and a brake booster issue. My initial thought was brake booster. Best to get a vacuum pump and give it a thorough test. Cheers Bennie That’s something I hadn’t thought of, just a slow reaction time... interesting. I’ve never noticed it in the other GLs I’ve encountered myself but sounds possible. A secondary leak sounds promising to me, but are you saying that’s only a possibility if I also have a bad booster? I may be misreading or misinterpreting what you said. Link to comment Share on other sites More sharing options...
G3.Spiffy Posted June 8, 2020 Author Share Posted June 8, 2020 (edited) On another note, took the car for a test drive just now. Went 11.8 miles (first real drive since the swap) with the only issue being what I can only presume is an intermittent fuel supply issue. I was driving down a hill of a decent grade and think I may have moved around my fuel (had a little less than a half tank) enough to pick up some air or debris with my fuel pump, either starving the engine of fuel or clogging up my filters or injector momentarily. The car bogged down quite a bit, then idled fine but the rpms would drop when throttle was given. Limped home and the issue got less noticeable and eventually went away just before I got back. Checked fluids just to make sure, and everything was good. Only code is a stored TPS code from the swap process that I haven’t cleared yet. The car was originally carbed, so it doesn’t have baffles in the tank and I haven’t installed a surge tank setup or dealt with that yet and I assume that might be the cause of my issue, but I’d like to know what others think of this as well. Edited June 8, 2020 by G3.Spiffy Link to comment Share on other sites More sharing options...
Eriklyon94 Posted August 18, 2021 Share Posted August 18, 2021 I have the same issue, feels like if I didn’t have the cat it would be backfiring, I can hear and feel an audible “coughing” Link to comment Share on other sites More sharing options...
el_freddo Posted August 19, 2021 Share Posted August 19, 2021 @G3.Spiffy - sorry for not getting back to you earlier. The NA tank without baffles shouldn’t be an issue - I ran my NA MPFI with the carb tank for ages and only had a power lull at times, I think it was the small return line. I never got to the bottom of that one as I swapped the tank out for an EFI unit and upgraded the return line when I went EJ. It could be a blocked filter. I doubt injectors would clear themselves up. You should sort out that TPS issue and get that out of the way. Also check your temp sensor for the ECU. If that’s out of whack it seems it can do some strange things from what I’ve read. @DaveT will be able to throw more light on the temp sensor info. Cheers Bennie Link to comment Share on other sites More sharing options...
Ionstorm66 Posted August 20, 2021 Share Posted August 20, 2021 For the idle issues check your IAC and make sure its clean. Also check for vacuum leaks. 1 Link to comment Share on other sites More sharing options...
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