Tbi runs strange

[87silveradok20]

So I have a 1989 crew cab 4x4. The truck has a tbi 350 in it. I have replaced one tank on one side and that tank has a brand new fuel pump in it. My problem is that the truck isn’t running right. Most of the time it will sit and idle fine. Sometimes tho it will have a surging idle to the point it almost dies or does die. When you are accelerating it will cut out like someone cut the fuel supply off to it and when you are going down the road you can hear it cut out very momentarily. It never bogs down it just cuts out. The part that confuses me most is it rarely ever does any of this when it’s cold. Pretty much only when warm. It has the egr blocked off so it’s not that. I’m going to try a fuel filter to see if that helps but I have a feeling that’s not it. It does this on either tank. The truck isn’t losing power when this happens as everything stays on when it happens (radio and heat). Does anyone have any ideas?


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[1987 GMC Jimmy]

No trouble codes when any of this happens? You said it’ll do a version of it when idling. I’d check for stable fuel pressure just to be safe and then replace the filter after you tee in the gauge. Borrow a tester from Autozone and no $ out of your pocket. The ICM is an important mediator of fuel and spark on these TBI motors. I’d remain open to having it tested to see what’s going on. They can work cold, and then go on the fritz warm. Of course, if it starts right back up and runs stably, probably not it. Maybe watch your injectors while this is happening and see if the spray pattern deviates to something abnormal. Is it running noticeably rich or lean? I would do a voltage range test and ground confirmation test on the TPS and maybe a pump up test on the MAP sensor. Also, does your SES light behave as it’s supposed to (comes on when you turn the key on)? Has the EGR been written out of the PROM? I don’t know about yours, but if I just unplugged mine, it’d notice pretty fast.

http://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/tp-sensor-tests-1

http://troubleshootmyvehicle.com/gm/2.2L/how-to-test-the-map-sensor-1

 

[HotRodPC]

I have a feeling it's going to be a sensor. Very possible even a temp sensor. About the check engine light... Is it on? Do you have an OBD1 code reader or know how to jump the ALDL to get the codes off the flashing light on the dash? If the CE light is on, I'd do that first and foremost. Get your codes.

 

[4WDKC]

If there is a CEL light on you have to fix that first as it will put the ecm into limp home mode and that can give you all kinds of false readings and ideas of what is wrong. If you didnt get the EGR tuned out that will give you fits too as the ecm is expecting to see the exhaust ported back into the engine so it cuts fuel and maybe timing. When its not added the ecm reads an undesired value from the o2 and tries to compensate. An exhaust leak coupled with the lack of egr can make the truck stumble and feel like its going to die, snort, pop then act normal again all while cruising at interstate speeds, mine did this due to exhaust leak and plugged egr passages.

 

[87silveradok20]

The CEL comes on like it’s supposed to when you go to start it. I don’t have the egr tuned out. I just took it off and put a block off plate on it. Today I was out driving the girlfriend around and it died. I couldn’t get any spray out of the injectors. I can hear fuel pumps kicking on in both tanks and the switching valve sounds like it’s working too. If I dump fuel down the throttle body it will fire off. Gonna put a fuel filter on in the morning.


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[1987 GMC Jimmy]

I’d put a noid light on the injector connectors when it does this to see if you’re getting a pulse. If not, I’d see about testing the ICM. If so, I’d go the course of the fuel filter and going from there. @4WDKC is right about the EGR. I know mine would throw a fit if I just blocked it off with the solenoid thinking all was well.

 

[4WDKC]

The TPS could be bad also, I had one that wouldnt start without adding something to the tbi because it was saying it was WOT which is clear flood while cranking. Need to get a scanner or laptop connected so we can see live data.

 

[87silveradok20]

Well I messed up I thought the cel was coming on but it wasn’t. Fuse was blown. I put a new fuse in and before I even cranked it I heard it pop. Does this mean my computer is fried?


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[4WDKC]

Well I messed up I thought the cel was coming on but it wasn’t. Fuse was blown. I put a new fuse in and before I even cranked it I heard it pop. Does this mean my computer is fried?


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ECM B fuse?

 

[87silveradok20]

ECM B fuse?

I think so. Is it the one below the wiper fuse. It’s a 10 amp. I’m not by the truck right now to check for sure


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[4WDKC]

I think so. Is it the one below the wiper fuse. It’s a 10 amp. I’m not by the truck right now to check for sure


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I dont remember the location I just know it blew when my truck died driving down the road and blew again when I replaced it. Turned out the bushing in my dist. wore out and allowed the inside of the pick up coil to contact the outs side. I bought a replacement dist. from local parts store, replaced fuse and truck started.

 

[87silveradok20]

I dont remember the location I just know it blew when my truck died driving down the road and blew again when I replaced it. Turned out the bushing in my dist. wore out and allowed the inside of the pick up coil to contact the outs side. I bought a replacement dist. from local parts store, replaced fuse and truck started.

Hm that’s something I will have to check into. Did it mess up your computer?


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[4WDKC]

Hm that’s something I will have to check into. Did it mess up your computer?


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no it didnt

 

[1987 GMC Jimmy]

I blew an ECM B and a GAGE/IDLE when a rat had chewed a spark plug wire, and the exposed part touched the frame. My ECM did burn then, though.

 

[87silveradok20]

I blew an ECM B and a GAGE/IDLE when a rat had chewed a spark plug wire, and the exposed part touched the frame. My ECM did burn then, though.

I checked the plug wires. All look good. No holes in them. The fuse that blew was ecm 1


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