TPI Sierra

Just started suddenly yesterday. Drove it for a week with no real troubles.

What it is: 1987 Formula 350 engine, stock, using stock 1987 Firebird harness in 1989 GMC Sierra. MAF system.

What it's doing: In park, it runs okay, revs up okay most of the time but once in a while it will start to run rough.

In gear, it chugs and backfires through the intake and has a bad hesitation but will eventually take off. Every once in a while it will go like nothing is wrong and idle okay.

What I have done: Compression test - all 8 show good compression; fuel pressure - 30-35 running in park or in gear, no fluctuation; Checked for vacuum leaks - found nothing major, the plenum bolts on one side were somewhat lose, I loosened all and torqued them to spec; vacuum gauge - 16 hg at idle; fluctuates rapidly now, was steady with a little fluctuation. Timing - dead on using a light and the vacuum gauge; EGR appears to be functioning correctly; no SES light; TPS is set correctly; I have not done any datalogging as I am waiting for a part to come for my ALDL cable, I have WinALDL, TunerPro and EFILive, which is best to use?; Checked the fuel injectors and all 9 are within spec.

I replaced the IAC yesterday, that's when it all started. I cleaned and put the old IAC back on and it's just as bad. I have the vacuum line under the TB hooked up, I've tried it with the CVC unhooked and plugged as it had been before I got it and no change; Did an idle relearn, no change; I tried doing a IAC reset but it will not stay running with the IAC unplugged for me to set the idle.

When revving it up under the hood, I do hear a slight hiss on the passenger side of the engine when I rotate the throttle but I remember my other TPIs doing that as well and it did it before all this.

As I said, it was running fine all week, but after replacing the IAC, it will not run worth a dang. Put old IAC back after cleaning and doing the same.

TPI Sierra

Small update, I haven't taken it out on a road test as it's too rainy but plugging in ALL the vacuum lines does help. Forgot the one under the TB.

TPI Sierra

Barely made it around the block, still running very poorly. Unhooked the MAF and it seemed to run better, can a MAF be bad without setting off the SES light?

aliceempire

iTrader: (14)

The port under the tb is for the egr and you said that should be functioning...did you plug the port on the tb? Or use it for the egr?

TPI Sierra

I hooked it back up but it runs better at idle but still bogs down. It runs better when cold but warms up, wondering if I might have done something with the CTS. It doesn't smoke at all and doesn't seem to run rich.

TPI Sierra

I replaced the fuel filter thinking it might have been clogged, no change. Just chugs when put in gear but idles okay.

TPI Sierra

fuel pressure is 31-32 at idle and doesn't move at all, even when unplugging the FPR.

aliceempire

iTrader: (14)

That's no good. You should roughly 43 with the vacuum line off. The vacuum, or lack there of, should raise the pressure when the throttle opens. So when the engine is WOT and the vacuum is lowered the fuel pressure goes up. Is there vacuum at the line? Is your regulator adjustable?

TPI Sierra

I was told it was fine. "Fpr should only change fuel pressure on change in load." was the exact quote from a friend that knows TPIs well.

I've replaced the IAC, TPS, all gaskets on the TB. Sick of throwing parts at it and replacing the IAC should NOT have caused it to do this. I've tried resetting the IAC and it won't run with it unhooked, half the time it won't even start now unless I push the accelerator down almost halfway. When it is running, it idles fine in park but chugs and pops through the intake bad in gear.

aliceempire

iTrader: (14)

I don't know your friend or their knowledge but with the vacuum line disconnected from the regulator, the fuel pressure should be 43. No "load" required. If you only have 35 with no vacuum to the fpr...then it is LOW.

TPI Sierra

Okay. So what would be the cause? The fuel pump is a new Delphi, the fuel filter is new. The engine is totally stock (as far as I know). All the injectors ohm out to 16-16.2.

I hooked up my fuel pressure gauge and now the fuel pressure goes to 30 psi and drops to near 0 after the pump shuts off. Pinched off the return line and it drops to about 10. I've pulled the plugs and none are wet. FPR bad?



The fuel pressure was at 30-32 when it was running well, so why would it not be good now after replacing the IAC?

I don't have the money to keep throwing parts at it and hope they work.

aliceempire

iTrader: (14)

30-32 with vacuum hooked up? If so then that's average. There should be a significant pressure difference between the vacuum line off and the line hooked up.

I think the iac was coincidence, unless you bumped something or broke something wiring related and didn't notice.

Regulator could be bad..does the vacuum line for it get fuel in it? That's the usual sign of a bad one. Pump is possible but it wouldn't be on the top of my list.

Also, why did you change the iac in the first place?

TPI Sierra

Yes, 30-32 with vacuum to it. Does not change when revved up or with no vacuum. It revs up fine in park or neutral, but in gear is when it does it's crap.

I've used carb cleaner and my friend's smoke machine and can find no vacuum leaks what so ever.

No fuel in the FPR vacuum line.

The idle was erratic and the IAC looked like the original so I just went ahead and replaced it.

aliceempire

iTrader: (14)

The pressure should be different between vacuum and no vacuum. That's why I asked way back if the line had vacuum (suspecting it clogged or broken). There's a problem there. Maybe the regulator spring is busted?

So there was a problem before this one, the cause may be one in the same.

TPI Sierra

Ordered up a new adjustable FPR, so we shall see.

Before it just had an erratic idle, no other problems. I planned to replace sensors like that with new as I could. I took the TB off to replace it as I had a new gasket for the TB.

I sincerely do appreciate your help here. Hopefully I can fix it and continue enjoying the truck because it was fun the week I had it running well.

aliceempire

iTrader: (14)

I hope you find the problem soon. As a Sierra owner myself I hope my help leads you closer to the problem.

maks10

Have to ask why you needed to set timing with a vacuum gauge with tpi? I'm not too savy on vaccum advance distributors but the light at 6 btdc should suffice?

TPI Sierra

I did it that way because I wasn't 100% sure if my balancer had walked. I still need to check that.

aliceempire

iTrader: (14)

Just have to ask to be sure....you changed the timing with the est disconnected, correct?

And a vacuum gauge helps tell where the engine is happiest when setting timing. Doesn't means it gets you to the best spot but can help. Especially if your unsure of the balancer.

Jersey89GTA

iTrader: (1)

Did you do the MAF - ? I went thru 3 of them in a year and a half ... 3rd one the charm.
Pricey little devils too. If using a K&N filter -oil will foul them. I learned the hard way.

maks10

[QUOTE

And a vacuum gauge helps tell where the engine is happiest when setting timing. Doesn't means it gets you to the best spot but can help. Especially if your unsure of the balancer.[/QUOTE]

Thank you for clarifying! back to diagnosing have you tried resetting iac again? This would at least eliminate some problems and using the new one would hopefully eliminate a stuck open iac (as would tuning software when that comes)

Doobie52

Do you have to crank the car over for an extended period for it to start? If so, it sounds like you need to check the fuel hose running between the pump and the sending unit inside the tank. You shouldn't be bleeding off fuel pressure so quickly after turning the car off, and your base pressure isn't high enough. Did you use submersible fuel hose when you replaced the pump? It doesn't take long for regular hose to degrade when submersed in fuel.

TPI Sierra

Replaced the fairly expensive FPR diaphragm and now it has almost no pressure but will start if I open the throttle half way. Very little pressure when it does start. I put the diaphragm in correctly, did I miss something?

No K&N and when I had rapped on the MAF with something, it didn't make a difference.

It won't run long enough for an IAC reset.

Yes, I do now. It started up right away before all this and even when it was running poorly but good idle it started right away. I used the hose that the new Delphi pump came with, I really don't want to have to take the bed off again because the tank is full....

TPI Sierra

Well, doesn't help when my fuel pressure gauge has taken a poop. Will report back when I get a new one.

TPI Sierra

Okay, new gauge acquired.

On a hunch, I hooked it between the fuel filter and line and it starts better now but still does the same. 30-32 PSI there, no change when revved up and when it is shut off, it immediately drops to 10-15 PSI so it looks like I'll be taking the bed off this weekend and pulling the pump. ARGH!!!!!!!!\

I did get to use WinALDL finally. It won't log without the 10K resistor in play. Only thing i really notice is that the BLMs creep up to 160 (which I know is fairly common on TPIs). My O2 sensor is a little slow but it's a little old too, I will replace it in a couple of weeks when I get paid.

maks10

That's showing lean at 160 when is that happening? Acceleration or idle? probably check your plugs to confirm if your lean most of the time

TPI Sierra

After it warms up, it starts at 128 of course but then creeps up to 160 as it warms up. Both idle and acceleration show no change.

When I pulled the plugs to see if the injectors were leaking, they didn't look like it was running really lean, the plugs were brownish/tan.

maks10

Should still hang around 128ish even after warm....good plugs seem ok (although may not have ran long enough to show lean) need to figure out lean condition though....need the fuel pressure to be corrected first and maybe that will correct this or at least help look elsewhere

TPI Sierra

Yes, the fuel pressure problem definitely needs to come first. Going to pull the bed tomorrow and pull the pump to see what is going on there. I have another pump if need be.

TPI Sierra

Never been a time when man has spent so much and gotten so little for his money.

Put in a Walbro 255 and other than a dead miss which is likely a burned plug from running lean, it goes like stink.

Need to take back this new Delphi junk.

m16a2r

Maybe your ignition control module is bad? I had some weird running issues couple of month ago, would run like crap 1 minute and then would run great the next, end up replacing ecu, now runs like a champ, solder joints failed on the board, chip was fine.

TPI Sierra

I might go ahead and replace the ICM, as I have a brand new one around here somewhere.

Right now all that seems to be the matter is a bad miss, I found the no. 8 plug burned and replaced it but still has a miss. Probably need wires, cap and rotor at some point as well.

no new tires

$40
http://www.ebay.com/itm/311025706666?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

TPI Sierra

Will have to look in to that. Thanks!!

no new tires

I paid 200 for mine. Diz was shot from being RUSTED. Then I saw this...still thinking about buying it out of spite.

m16a2r

Well if everything else fails, and your car still acting up and you have spare ECU try to swap it. But its strange that your fuel pressure drops so fast, i never seen that in my car before, it usually maintains it for a long time.

TPI Sierra

Unfortunately, I don't have a spare ECM. My mom is about to junk a 1989 GMC S15 that has a new one though and it should have a '259 ECM in it so I need to ask her to pull it for me and ship it just to have.

The fuel pressure still drops but takes a while and it starts right up now so I am not really worried about it now.

m16a2r

If your fuel pressure drops right after you turn off your truck that means you got a leak in the fuel line, you should not have no sudden pressure drops at all. My gta would maintain same pressure for an hour or so.

TPI Sierra

Hmm...Have to look in to that. There's no drips in the driveway and no visible leaks on the engine. Perhaps the injectors are leaking, I plan to replace them in the near future anyway though they ohm out at 16.4 on all 8 but that doesn't mean they aren't leaking.

m16a2r

dont want you to guess and buy bunch of parts anymore, as far as I can tell, my gta will maintain the fuel pressure for a long time, check your fuel system for leaks, all of the fittings, one might be leaking slightly. I had my brothers corvette leaking fuel just barelly out of one of the fittings by fuel filter, it would not run for nothing, found one fitting loose, after tightening it, the car ran great.

TylerSteez

iTrader: (3)

leaking injectors is another possibility for why your fuel pressure drops rapidly after the pump shuts off,

TPI Sierra

Dead miss fixed, seems the midget penguins in the A/C system got out and partially unhooked the no. 8 fuel injector.

Whenever it quits raining, I will look in to leaks in the fuel system.