1999 c 2500 engine 5.7L vortec . When I accelerate without the turn signal on it runs great. When I have turn signal on the engine looses power when blinker lights up and clears up looses power and clears up. I have a new fuel pump , battery , alternator. I’m stumped on what could be the issue? Any help would be appreciated

 

i would be checking the grounds. even the ones on the motor/firewall/battery

 

Ok thanks I’ll try and see if it helps keep u guys updated

 

I cleaned the grounds on frame , engine , and battery connections . The fuel pump is brand new . The ignition system has been rebuilt with new oem parts . But when I accelerate without turn signal on it accelerates great no power loss. But when I engage the turn signal under acceleration it surges in sync with the turn signal. Almost like the fuel pump is losing power during the time the blinker engages. I am stumped on what could be the issue. If I run any other electrical components it doesn’t affect the engine power or acceleration only the turn signals.

 

you might have short in your turn signal circuit. does it run better if you pull the lamp fuse?

 

I’ll try it and see what results I get. I replaced the engine about a year ago with the same type engine that came in the truck from factory. It doesn’t lose any power unless I’m accelerating pretty good and turn either blinker on. It doesn’t stall or die out . When the signal is illuminated it loses about 200 rpm and when signal goes off it returns to normal rpm during acceleration . It’s really got me scratching my head . Especially when entering a interstate hwy ramp with my signal on I gain speed and lose it gain it lose it . It’s kinda funny to experience.

 

That's interesting. I'll have to agree with the other poster and say that you either have a bad ground somewhere or you have a chafed wire in the directional circuit that is shorting to ground.

 

Thanks for the info I’ll have to dig into the wiring diagrams

 

It is strange. I’d have guessed grounds first too but if those are good.....?
I have hard time seeing how you can have a short or “semi-short” on something related to turn signals which either doesn’t blow a fuse or, if just drawing enough current without blowing fuse to mess up fuel pump or ignition, you don’t have similar issues when AC kicks on or bright lights , etc.

i don't mean to insult but are you sure it’s running “normally” when blinkers aren’t blinking? I had a problem once where idle was rough but drove fine otherwise. It ended up being marginal fuel pressure (this was a 93 TBI). After replacing fuel pump I realized it hadn’t been driving fine- there was so much more power! I hadn’t noticed the loss of power because it went bad so gradually. Things going slowly bad are hard to notice. Kinda like when I woke up one day and noticed I was 30 lbs heavier with a gut.

Even though fuel pump is new, I’d suggest checking fuel pressure to confirm it’s solid and not marginal, stays solid with punching throttle. You could also potentially see if if varies with blinkers. You didn’t say if you replaced the filter at same time but if you didn’t you should. Also - what brand pump? I don’t have experience with the higher pressure fuel pumps but have read many threads where brand new pumps were marginal. People with experience seem to favor ACDelco or Delphi.

good luck, I’m interested in hearing what turns out to be the problem.

 

When I replaced the fuel pump I used a acDelco brand pump. And you maybe right now that I think more about it. I run the AC all the time in the truck . It starts great accelerates well as long as I don’t engage the signal . But when I come to a stop light the rpm does fluctuate up and down some about 300 rpm It’s not a steady idle all the time. But soon as I accelerate it clears up . If I disengage the ac compressor it also clears up . I suppose the two issues could possibly be related.