• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

BII with engine running rough question


dispatchrobb

Well-Known Member
Joined
Sep 15, 2011
Messages
70
Vehicle Year
1989
Transmission
Manual
89 BII 2.9 rebuilt with 5 speed.

The engine sounds normal but when at low speed especially in 3rd and 4th the engine shudders. You can tell it shudders a little as well when idling and runs rough like it's missing, but all plugs look normal. No wet plugs or misfires or codes of any kind.

No vacuum leaks, I have a gauge on it and it's steady at 19, and operates normally when driving. But when sitting I can hear what sounds like a leak until I apply the brakes and the leak goes away until I release the brakes and it comes back. Is this something that is normal, or will that go along the lines of the engine shuddering.

I am at a loss.
 
I would certainly look at the power brake booster.

Power brake booster should be air tight, at the booster end of the hose is a check valve, this holds vacuum in the booster so you have power assist for 2 or 3 pedal presses if engine should stall out while driving.
If you pull off the booster hose from intake and then suck on it, lol, or use a pump, it should hold vacuum, not slowly leak out.

Just to test for a possible vacuum leak, have engine warmed up and idling at 700-750rpms(manual trans idle target for computer), now unplug the IAC Valve.
Idle should drop to about 500rpms or engine may even stall, either is OK because it means there is no vacuum leak causing your issue.
If idle stays up then there is a leak somewhere.
With IAC Valve unhooked remove one vacuum line at a time and plug intake port with your finger, when idle drops you found the leaking system/hose.

The 19" at idle would seem that there is no leak, but on a fresh rebuild you could have 21" so hard to say for sure.

1989 2.9l will use a MAP sensor for air/fuel mix, MAP sensor should be on the firewall passenger side towards the center, it will have a vacuum line attached and electrical connector, check the vacuum line, remove it and check that it is air tight.
MAP sensors rarely fail, not never but rarely.

Seafoam in the gas tank can help clean out injectors, I use a can once a year in my 4.0l.

If you have a timing light check if timing is drifting at idle or stable.
TFI systems are just old now and can have issues, good read here with tests: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml
 
Last edited:
Ok, warmed it up and unplugged the IAC valve, engine stalled. So that was good. However, you can hear hissing in the break booster, and appears that test it slowly leaks out. When I turn it off, you can hear hissing till it dies off from the booster, it's louder from inside than listening to it from the engine side. When running, brakes work just fine, but turn it off, and after hissing stops, there's no assisted brake pedal.

I took out plugs to check them, and the number 6 plug ceramic is a tan color and looks like a slight oily sheen, all other plugs ceramic were pearly white and dry. Plug fires fine, but not sure if that cylinder is the issue where it seems like the engine is missing or not. No engine codes or anything like that.

Not sure if there would be an injector issue there or not, but wouldn't that throw a code if there was?
 
Non specific advice. Fix what you know is wrong first. Trying to chase two problems at once just leads the drinking!!

Now plug the brake booster line and see if the hissing stops. If so you have a leaking/failing brake booster.
 
Update... finally got around to messing with it. The brake vacuum appears to be coming from around the pedal, it hisses under the dash up under the pedal when applied, and continues to hiss, but when I pull, with my hand, the pedal to full return, the hissing stops. Is there something around the pedal that would hiss like that?

The rough running issue that has been eluding me, turned out to be an injector plug that was not plugged in. The shop that rebuilt the engine apparently wasn't so bright, they didn't have the number 6 cylinder injector turned to where the plug was supposed to be, it was wedged between the distributor and fuel rail, so the genius whittled off the connector to just the wire prongs and tried to jam it in... which it still didn't fit. So I took the 10 minutes needed to remove the distributor, twist the injector, and wire a new pigtail on it, and wow, no more rough running engine.
 
Yes, the power brake booster uses an atmospheric valve on the brake pedal side.
Engine side of power booster holds a vacuum(less than 15psi), when you press the brake pedal outside air pressure(15psi at sea level) rushes in thru the atmospheric valve and 'assists' your foot pressure on the pedal.

Diagram here: http://www.agcoauto.com/content/news/p2_articleid/129

If atmospheric valve is leaking you will hear the engine vacuum continually sucking in air.

Cruise control also has a vacuum valve on the brake pedal, if cruise control is active touching the brake pedal opens this valve which cuts off cruise control.
This diagram shows the Vacuum Dump Valve: http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Cruisecontrol_1of2.JPG
 
Last edited:
The running issue is still not good. Today when I started it up, it ran very poorly, it was about 25 degrees out. On the highway, I had the pedal to the floor, going about 60, and the tach was only at about 2400 rpms, and wouldn't go any faster at all, like it was struggling. As it warmed up, it got a little better, and the rpms came up, but fluctuated about 500 up and down... going same speed, flat and smooth road. It still sounds like it's missing, but no codes, spark at every plug.
I guess the next thing would be if an injector was not functioning? Not sure why it did what it did when it was cold.

Update: Finally got it figured out. There was another injector, that one of the injector prongs had been mashed into the fitting, so it wasn't making connection, giving me all these issues. So I fixed one injector, sort of got better, found and fixed the other injector, and engine runs smooth, no more issues.

Thanks and happy new year!
 
Last edited:

Sponsored Ad


Sponsored Ad

TRS Events

Member & Vendor Upgrades

For a small yearly donation, you can support this forum and receive a 'Supporting Member' banner, or become a 'Supporting Vendor' and promote your products here. Click the banner to find out how.

Recently Featured

Want to see your truck here? Share your photos and details in the forum.

Ranger Adventure Video

TRS Merchandise

Follow TRS On Instagram

TRS Sponsors


Sponsored Ad


Sponsored Ad


Amazon Deals

Sponsored Ad

Back
Top