89RSRedConv

iTrader: (2)

Ok, here is a description of what happens when this car is on the road. I let my foot off the gas and the car will idle fine then surge forward then idle fine not in any pattern and not all the time. If I am stepping on the gas it will go then lose power then go again, again not in any pattern and not all the time. It seems to run fine for a few minutes then will do this and it will get less and less pronounced over time, but it did not go away. I went out and it was really bad I stopped to get the camera so I could post a video and it became less pronounced and the camera was not all that helpful including several dramatic slides off the dash.

As I understand this 5.0L 305cid V8 TBI (E) OHV engine it is for the want of a better tem a “hybrid” it is fuel injected but there are not 8 fuel injectors? There are only the two on the top of the TBI that shoot in to the TBI (which is for all proposes a carburetor)? It has been suggested that I remove these and soak them to clean them out (buildup would not surprise me as the IAC was caked in carbon) or replace them if they are not too costly. I do not want to fool with computer settings so stock would be fine with me.
He told me what to soak them in it was from Chevy it was “top …. something” any thought?

I have searched the boards and found a couple places that sell these and that they are a bit confusing as they seem to sell sets of 8 which I do not want. I think I need this ACDELCO Part # 2172285 there are two listed for automatic and I do not trust the guys at the counter all that much.
Also I have searched for a thread on how to remove these and had no luck so if you know of one let me know.

I have replaced the IAC and all the gaskets and checked many of the vacuum lines.

So what does it sound like to you?
Your help is greatly appreciated.

ntomsheck

iTrader: (1)

This was actually a very popular engine configuration of the late 70's and the 80s (even some of the 90s. You don't see it on any factory cars today, because there are many better options. The piece that is the brother to a carburettor is called a throttle body, synonymous with the throttle body on a MPFI (# injectors = #cylinders)

You don't have to clean the injectors in any special fluid, you can usually just put them under brake fluid to take the deposits out. Then, use a multimeter to test the driver coils. It sounds less like an injector issue, and more like a fuel delivery issue. Replace your fuel filter, then test you fuel pressure during prime and during running. If it drops when it does it's loss of power routine, then you need a new pump. Someone with more TBI experience will jump in and tell you what pressure you need (I think it's around 14-15psi).

uraijit

Is it doing this when the engine is cold, when it's warm, or both?

I believe the GM part number for the 305 injectors was GM 5235279 *RPD, according to the DIY-EFI page.

The pressure will be somewhere between 9-14 PSI (Chevy wasn't too particular about what they set the pressure on the regulators to, off the assembly line.

The fuel filter, fuel pressure test, and an injector cleaning/replacement is a good place to start. You can also use a battery to momentarily click the injectors open, and then use the tube on a can of carb cleaner to "Back flow" the injectors. Don't leave the battery hooked up for more than a couple of seconds at a time though.

89RSRedConv

iTrader: (2)

It seems to be fine getting up to temperature, so I would say it does it after that. I will start out with the fuel filter and work from there, cheapest start works for me, LOL

I also saw a post about the power box? and it providing power randomly to the fuel pump due to a loose mount? that car was 91 mine is an 89 testing the PSI would let me know if the fuel pump was working, I assume?

I am hopeful it is the filter. Thanks guys I will report back.

89RSRedConv

iTrader: (2)

Replaced the fuel filer, took a bath, but it was better but did not solve the problem, going to work on fuel injectors next. I put up a video on my blog on the car. If you have a chance to look at it feel free to shoot of thoughts on what is going on with this engine. Have not replaced the fan belt either that is on list.

http://fatsquirrel.us/F-body/?p=359

Thanks

uraijit

Here are a few more things to try.

First off, was the AC running? If so, try it with the AC off, and see if that changes anything.

Secondly, try unplugging the MAP sensor. Does it smooth out when you unplug the MAP sensor?

Still need to check fuel pressure as well, since that could be part of and/or THE issue.

Also, check and make sure that the timing is set correctly. Should be set to TDC (0*) from the factory. Make sure it hasn't been messed with.

89RSRedConv

iTrader: (2)

The Ac was not running.
I unplugged the electric and it stalled immediately, I unplugged the vacuum and it stalled immediately.

I am uncertain if I am equipped to check fuel pressure or set the timing.

I am still wondering if it is getting air through a vacuum hose, going o check the all again.

Damon

There is no valve where you can hook up a fuel pressure gague on a TBI engine. No idea why they didn't design one in, but they didn't. Only way to test is to tap into the feed line (the larger 3/8" hard line going up to the TB. The smaller 5/16" line is the return).

Vacuum leaks are the first thing to check when the idle or part throttle drivability start going away. Had one that ran lousy under largely non-repeatable conditions. Turned out the factory PCV line had a huge split on the underside where it wasn't obvious. Replaced the line and ran like a champ for another 100,000 miles.