87 r10 350 TBI runs rough

[bash]

My 350 TBI is running very rough. I have repaired a few things:

1. Leaking intake gasket (Leaking oil from the valley)
2. EGR solenoid replaced (Hose was connected to vent. Hose barb was broken)
3. Leaking vacuum hoses replaced
4. Tightened loose spark plug
5. Replaced fuel filter

Here is the rest of the story. A month ago the idle became a little rough (I could notice it, nobody else seemed to notice it) after moving the spark plug wires to a loom. I thought that maybe I disturbed the vacuum system in some way but could not find any leaks. I later realized that the EGR solenoid hose was on the vent nipple and the actual hose nipple was broken off, so I replaced that. A couple of weeks later the truck started dying after running for an hour or so. Once the engine cooled down it would run again. If I forced it to run when it wanted to die by cranking it over and over I would get detonation and backfires. I couldn't find the exact problem but noticed that the intake was barely leaking a little water out of the front of the gasket and had been leaking oil out of the valley so I went ahead and replaced it. Now the truck idles/runs rough still but in a different way. When I crank it sometimes it seems to idle and run fine. If I rev it to 2k rpm on the third rev it starts to run rough. On that rev if I let off of the gas quickly it will fumble and die. When I am in traffic from a stop when warm if I hit the gas too quickly it will die. I have to delicately give it gas to keep it from dying. Sometimes it hesitates then jumps. Also when slowing down and especially if slowing down and turning it likes to die. I am constantly having to crank it after dying while driving down the road. Normally after coming to a stop or turning or going around a tight curve at a low speed. It seems like turning to the right is more likely to kill the engine than left. The engine is about five months old and has around 4000 miles on it. It is a brand new GM Goodwrench long block. I should mention that I was rear ended very hard about a month ago and a week or so before that I ran out of gas on the interstate. I believe that I turned the key off when that happened, but the fuel pump runs constantly when the key is turned on. It doesn't cut off after a few seconds like it is supposed to when the engine is off. I guess the previous owner hard wired it to a switched source. The pump does run and you can hear it like you always have been able to. The other tank is rusted through so I cannot switch tanks to see if it is a FP issue. Can anyone help me with what I need to be checking?

 

[bash]

I just went out to crank the truck and it wouldn't crank at all without hitting the gas pedal. I took the IAC out and cleaned around the spring and wiggled it around and it cranked and ran smooth for a couple of minutes then started the same thing again.

 

[HotRodPC]

Have you taken the EGR valve itself off and cleaned it? Sometimes they get carbon build up on the them, then when they need to close they can't due to a piece of carbon causing an internal vac leak in the intake.

 

[smoothandlow84]

When is the last time you changed the frame mounted fuel filter......and the sock filter on the fuel pump in the fuel tank?

Another fuel related item....check the rubber hose that is mounted on the in tank fuel pump. When it comes loose...all kinds of fuel and running issues pop up.

 

[1987 GMC Jimmy]

I agree with both responses. It would be a good idea to check out your fuel pressure and see if you need to tear into the tank. You can borrow a fuel pressure tester from AutoZone. It should tee into the fuel filter location. Summit Racing also sells an Actron adapter that threads in behind the throttle body, and the fuel line threads into the adapter. You should be getting 13 pounds of pressure. As far as the pump running after the engine shuts off, I'd look into the oil pressure safety switch being bypassed. It'll be located underside by the oil filter. I'm going to attach a thread I just commented on that talks about searching for vacuum leaks in detail. I also talked about IAC relearn there, too, which you should try.

http://www.gmsquarebody.com/forum/showthread.php?t=18177

 

[bash]

@HotRodPC:
When I replaced the engine I cleaned the intake from the underside. I never actually took the EGR off, but cleaned everything that I could access from the underside of the manifold with the TBI off.
@smoothandlow84
I replaced the fuel filter a couple of days ago. I have never checked the sock filter or removed the pump assembly from the tank for that matter. The pump was definitely direct wired to the fuse block, bypassing the oil pressure switch. I don't know why, but I would guess that the switch was bad or there was a problem with the wiring or tank selection wiring and they did this to keep from having to replace or properly troubleshoot it. I would have fixed it during the engine swap, but I didn't realize it was a problem and not wired correctly until now. When I have some more money I want to replace the rusted out passenger side tank and repair any issues with the tank selector system, but for now I just have to get it running with the one tank.

I will take the EGR off and clean it tonight and make the IAC run its relearn program as well as check the fuel hose mentioned. I won't be able to get my hands on a FP guage setup until this weekend. I will post back after checking everything else. Thanks

 

[bash]

I ran the IAC relearn and it runs much better now. The relearn seemed odd though. I haven't done this procedure before, but it seemed odd that when I jumpered the ECM pins and turned the switch on the IAC seemed to run non stop. It immediately started turning once the key was on and did not stop clicking until unplugged. The first time I tried the procedure I left it plugged with the key on for over a minute to see if it would stop, but it never did. The second time I waited 30 seconds and unplugged the IAC while it was making noise like it was still trying to turn. Does this imply that it is trying to turn further than it can? I am thinking that maybe it thinks that fully closed is further than it really is. This would cause a flooding condition right? The engine seems like it is flooding. Now it idles much better, not perfect, but close. When I rev the engine it doesn't die anymore, but when I let off of the gas about the time that the tach reaches idle speed again it stumbles some. Now it isn't enough to kill the engine, but it is noticeable. It does the same thing when driving and I let off of the gas. Even before it seemed like it only died when it had no load and the TBI main air was closed off from the pedal being let off of. I am going to clean the EGR tonight.

Can anyone tell me the correct connections for the vacuum line that comes off of a fitting on the back passenger side of the intake manifold? Right now it tee's off and runs to a very small hose that goes back through the firewall (it is a more smooth and plastic type than normal vac lines) and the other side runs to a plastic ball in the driver side corner by the firewall. I believe that there is supposed to be a check valve or something like that in this vacuum circuit but don't recall for sure. I removed the cruise control parts during the engine swap and don't plan to ever reinstall them so the vacuum system is a little simpler than it was. What is that ball for? Is that hose that runs into the firewall a vacuum source for actuators in the vents?

 

[1987 GMC Jimmy]

I ran the IAC relearn and it runs much better now. The relearn seemed odd though. I haven't done this procedure before, but it seemed odd that when I jumpered the ECM pins and turned the switch on the IAC seemed to run non stop. It immediately started turning once the key was on and did not stop clicking until unplugged. The first time I tried the procedure I left it plugged with the key on for over a minute to see if it would stop, but it never did. The second time I waited 30 seconds and unplugged the IAC while it was making noise like it was still trying to turn. Does this imply that it is trying to turn further than it can? I am thinking that maybe it thinks that fully closed is further than it really is. This would cause a flooding condition right? The engine seems like it is flooding. Now it idles much better, not perfect, but close. When I rev the engine it doesn't die anymore, but when I let off of the gas about the time that the tach reaches idle speed again it stumbles some. Now it isn't enough to kill the engine, but it is noticeable. It does the same thing when driving and I let off of the gas. Even before it seemed like it only died when it had no load and the TBI main air was closed off from the pedal being let off of. I am going to clean the EGR tonight.

Can anyone tell me the correct connections for the vacuum line that comes off of a fitting on the back passenger side of the intake manifold? Right now it tee's off and runs to a very small hose that goes back through the firewall (it is a more smooth and plastic type than normal vac lines) and the other side runs to a plastic ball in the driver side corner by the firewall. I believe that there is supposed to be a check valve or something like that in this vacuum circuit but don't recall for sure. I removed the cruise control parts during the engine swap and don't plan to ever reinstall them so the vacuum system is a little simpler than it was. What is that ball for? Is that hose that runs into the firewall a vacuum source for actuators in the vents?

That's a vacuum storage canister, but I call it a ball, too. And yes, that other line that goes into the firewall is for the different HVAC settings. The blend is mechanical so it's just to switch around to the different settings. There is a little HVAC control check valve. Most of them split to go to the cruise control, as well, but since you're not running it, I'm sure the Dorman 47170 check valve that they sell at all the parts stores would be just fine. Oh and with the IAC, mine does that, too. It'll just keep whirring forever if I let it. I think you're getting closer to solving it totally. Besides the EGR, have you had a chance to look at the other stuff that I mentioned in the thread I attached?

 

[bash]

Took EGR off and it is clean as can be. Sucked on hose and it pulled in. When I blocked off the hose it stayed in and didn't leak down. No vac leaks that I can find. After the IAC relearn it seemed to run almost perfect, then started getting more and more back to how it has been misbehaving. It just seems like it isn't getting enough air or too much gas one of the two. I have not been able to check fuel pressure yet.

 

[bash]

So after taking the EGR off to check it and bolting it back on the truck will barely run even at idle. It is throwing MAP, TPS, and EGR codes now. I have no clue no. Any help guys?

 

[HotRodPC]

You know it's going to be something simple being overlooked. I wonder if @89Suburban can find a minute to look over your posts and make a suggestion or a link to some troubleshooting he's done on his. He's become almost expert level on TBI.

 

[bash]

So I took it to a local shop and he checked everything using a scanner including looking at the data in real time. I must have damaged the EGR because deleting it fixed the majority of the problem. He installed a block off plate and suggested that I leave it and that there was no downside to that. I don't want this thread to become an EGR delete debate, but I am leaving it off until everything is solved and then installing a new one.

Since deleting the EGR it runs OK except it stalls sometimes when I put it in gear or especially when coming off the gas pedal and turning right. Odd that it is only right turns, never left it seems. Although it idles at 650 rpm it is slightly rougher than it used to be. Idle in gear seems a tad low.

Where to from here?

I should add that passenger side exhaust is loose due to being rear ended. It has broken loose from where it was held up about half way down the pipe. I can raise and lower the pipe with minimal effort by hand and one bolt came out if the collector flange.

 

[HotRodPC]

I was really surprised when you said the EGR was all good cuz it did sound like an EGR problem. So that mystery is solved.

Turning right?!?!? Hmmmm, if it was a different model vehicle I'd say check your oil level that when you're turning right, you're losing oil pressure for that second and it's shutting off the fuel pump but I don't believe this model has low oil protection.

 

[bash]

The fuel pumps should get their power through the oil pressure switch after the engine cranks but someone bypassed that and wired the pump directly to a switched source; yet another thing that works, but needs to be corrected.

 

[bash]

I just noticed that he didn't actually install a block off plate. All he did was stuff a ball bearing in the hose that connects to the EGR valve. If there were actually something wrong with the EGR valve how could this solve the problem? Isn't a bad EGR valve either stuck open or stuck closed? I'm confused now.

I found a small hole in the metal vac line to the brake booster. Patched it and I haven't stalled out again yet. Keeping fingers crossed. I still need to figure out what is up with the EGR though. If plugging the hose but leaving the EGR valve on solved a problem then it seems like the EGR valve is OK and the problem is that something is making the ECM turn the solenoid on at the wrong time.